My career has been in farm animal nutrition, animal health and number-crunching in the tropics, subtropics and UK.
I believe we must reduce the impact of livestock production on global and local ecosystems everywhere -- this must include reducing the nutritional need and social pressure) for eating large servings of meat & milk in human diets.
There is always the imperative to make sustainable use of land -- by developing low-footprint humane and healthy animal production systems rather than simply increasing efficiency -- and by promoting human health through controlling zoonoses and spreading the word on the science of nutrition.
Happy to help - consultancies welcome! Address: Reading, Reading, United Kingdom
JOURNAL OF AGRICULTURAL SCIENCE (CAMBRIDGE) 129: 353-366 (1997)
Annual variation in the feeding... more JOURNAL OF AGRICULTURAL SCIENCE (CAMBRIDGE) 129: 353-366 (1997)
Annual variation in the feeding value of barley straw (Hordeum vulgare L. subsp. vulgare) is economically significant in the Mediterranean region. The relationship between the feeding value for sheep of several winter-planted barley cultivars and monthly meteorological data was analysed at Tel Hadya, northwest Syria (mean annual precipitation 330 mm) in 11 years. Indicators of feeding value included contents of neutral detergent fibre, acid detergent fibre and nitrogen (11 years), voluntary straw intake by sheep (10 years), voluntary digestible organic matter intake (9 years), in sacco dry matter loss and lignin content (8 years), in vitro digestibility (7 years), and in vitro gas production (6 years). Monthly meteorological data included total precipitation, mean minimum and mean maximum air temperatures. Conditions likely to decrease grain yield tended to increase the feeding value of straw. Low mean minimum temperature in February, low precipitation in January, February, March and April, and high mean maximum temperature in March, April and May increased one or more indicator of straw feeding value (by both bivariate and multiple regression, P<0.05). Precipitation before January affected grain and straw yield but had little effect on the feeding value of straw. Genotype × year interactions had a meteorological component; the superior feeding value of the straw of locally-adapted cultivars vs. exotic cultivars was only seen in years with cool or wet springs. This has implications for the genetic selection of crops with better straw feeding value. Models based on monthly precipitation and temperature, calibrated for locations in the Mediterranean region, can predict the nutritive value of straw and aid the planning of rations for small ruminants.
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting th... more Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (''whole herd slaughters'' or ''depopulations'') that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
A novel method for estimating specificity of the Single Intradermal Comparative Cervical Tubercul... more A novel method for estimating specificity of the Single Intradermal Comparative Cervical Tuberculin (SICCT) test for bovine tuberculosis (bTB) using surveillance tests results is reported. The specificity of the SICCT test at three cut-offs was estimated from the dates, locations and skinfold measurements of all routine tests carried out in Officially TB Free (OTF) cattle herds in Great Britain (GB) between 2002 and 2008, according to their separation (by distance and time) from known infected (OTF-withdrawn) herds. The proportion of animals that tested positive was constant (P>0.20) when the distance between tested herds and nearest infected herd exceeded 8 km. For standard cut-off, calculated specificity was 99.98 per cent (95 per cent confidence interval ±0.004 per cent), equating to one false positive result per 5000 uninfected animals tested. For severe cut-off it was 99.91 per cent (±0.013 per cent) and for ultrasevere cut-off (selecting all reactors and inconclusive reactors) it was 99.87 per cent (±0.017 per cent). The estimated positive predictive value of the test averaged 91 per cent and varied by regional prevalence. This study provides further evidence of the high specificity of the SICCT test under GB conditions, suggests that over 90 per cent of cattle currently culled using this test in GB were infected, and endorses slaughter of at least these cattle for bTB control.
by Goodchild, A. V., Downs, S. H., Upton, P., Wood, J. L. N., de la Rua-Domenech, R. (2015) Veterinary Record, published online September 2, 2015.
The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of... more The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of cellular immunity (the skin, gamma-interferon and lymphocyte transformation tests). Tests of humoral (antibody) immunity, Mycobacterium bovis PCR probes on early tissue cultures or live cattle specimens, and tests based on &quot;electronic nose&quot; technology have been developed more recently. The key measure of diagnostic test accuracy is the relationship between sensitivity and specificity, which determines the false-positive and false-negative proportions. None of the tests currently available for the diagnosis of bovine TB allow a perfectly accurate determination of the M. bovis infection status of cattle. Although various factors can reduce the sensitivity and specificity of the skin tests, these remain the primary ante mortem diagnostic tools for TB in cattle, providing a cost-effective and reliable means of screening entire cattle populations. Despite the inescapable limitations of existing diagnostic tests, bovine TB has been effectively eradicated from many developed countries and regions with the implementation of sound programmes of regular tuberculin skin testing and removal of reactors, coupled with slaughterhouse surveillance for undetected infections, repeat testing and culling of infected herds, cattle movement restrictions to prevent introduction of infected animals and occasional slaughter of entire herds with intractable breakdowns. This is likely to remain the mainstay of bovine TB control programmes for the foreseeable future. Additionally, newer ancillary in vitro diagnostic assays are now available to TB control programme managers to supplement the skin tests in defined circumstances according to the specific disease situation in each country or region. The strategic deployment of ancillary in vitro tests alongside the primary skin tests has enhanced the detection of M. bovis-infected cattle and reduced the number of animals slaughtered as false positives.
This report, provided by the Animal and Plant Health Agency, summarises the infection status of b... more This report, provided by the Animal and Plant Health Agency, summarises the infection status of bovine TB in cattle in Great Britain from January 1 to December 31, 2013 and describes some of the temporal trends observed over a longer period. It updates the previous annual summary for 2012, also published in the Veterinary Record vol. 174: 600-604 (2014).
Broughan JM, Harris KA, Brouwer A, Downs SH, Goodchild AV, Upton PA, Smith NH. Veterinary Record 176: 326-330 (2015).
Experimental Agriculture 40: pp. 277–294 (2004).
DOI: 10.1017/S0014479704001814
Straws and sto... more Experimental Agriculture 40: pp. 277–294 (2004). DOI: 10.1017/S0014479704001814
Straws and stovers are often called ‘by-products’ of grain production even though they are increasingly important, e.g. for animal feed, thatching, soil improvement, mushroom production and industrial use. As a result, plant breeders, agronomists, economists and animal nutritionists have to pay more attention than before to the total value of crops, i.e. whole plant value in which straws and grain both play a part. This paper reviews literature about the technical potential of breeding and/or management for more or better straw. It then discusses issues of the economic value (EV) and nutritional value (NV) of straw and stovers for livestock feed to guide research and development in cereal breeding and management. It is mainly based on experiences from the Indian subcontinent and semi-arid regions of the Near and Middle East. The paper shows that the quantity and quality of straw produced has changed considerably over recent decades as a result of breeding policies, new cultivation patterns and choice of cultivars. Both EV and NV depend on type of grain, animal production system and access to other feeds. A classification of these factors is provided and suggests that the EV of straw is particularly important in low-input systems with stovers from coarse grains.
Options Méditerranéennes, Série A. Séminaires Méditerranéens; n. 34. Seminar of the FAO-CIHEAM N... more Options Méditerranéennes, Série A. Séminaires Méditerranéens; n. 34. Seminar of the FAO-CIHEAM Network of Cooperative Research on Sheep and Goats, Subnetwork on Nutrition, 24-26 Oct 1996, Rabat (Morocco). Zaragoza : CIHEAM, 1997. p. 87-92.
In sheep fed diets containing ad libitum barley straw, body weight change is closely correlated with straw intake. We are finding that it is more effective to select genotypes for straw intake using calibrated indirect tests than by conducting intake trials with sheep. Not only are the tests cheaper, but the test results are more heritable, even when their genotypic correlationw ith intake is allowed for. Of the tests, Near Infrared Reflectance Spectroscopy is the most effective, followed by in sacco dry matter loss, acid detergent fibre, pair-preference tests in sheep, and in vitro gas production with rumen fluid.
PLOS One 7(8): e43217. doi:10.1371/journal.pone.0043217.
Bovine tuberculosis (bTB) is one of th... more PLOS One 7(8): e43217. doi:10.1371/journal.pone.0043217.
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (‘‘whole herd slaughters’’ or ‘‘depopulations’’) that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
Veterinary Record 174: 600-604 (2014). doi: 10.1136/vr.g3644
This report, provided by the AHVLA... more Veterinary Record 174: 600-604 (2014). doi: 10.1136/vr.g3644
This report, provided by the AHVLA, summarises the infection status of bovine tuberculosis (TB) in cattle in Great Britain from January 1 to December 31, 2012 and describes some of the temporal trends observed over a longer period. The AHVLA intends to produce similar reports for future years to provide a concise summary of how the situation is developing.
Annual conference of the Society for Veterinary Epidemiology and Preventive Medicine, Espoo, Hels... more Annual conference of the Society for Veterinary Epidemiology and Preventive Medicine, Espoo, Helsinki, Finland 2007 (poster).
Since herd sizes have been increasing in the last 40 years and the probability of a herd being infected increases with herd size, could that explain the rise in bovine TB? However, - The bovine TB rise happened c. 20 years after the increase in average herd size - The probability of an individual animal being confirmed with TB doesn't vary with herd size But herd size is still very important: - Herd size increases the probability and duration of bovine TB incidents. This affects the economic and animal welfare problems caused bu bovine TB.
Annual Conference of the Society for Veterinary Epidemiology and Peventive Medicine, Edinburgh 20... more Annual Conference of the Society for Veterinary Epidemiology and Peventive Medicine, Edinburgh 2012 (poster)
An analysis of the data used here by stepwise logistic regression using eight types of covariate confirmed the following results • Subtracting the Avian reaction from the Bovine reaction when selecting TB reactors may not always be the most accurate way to detect infected animals • In particular, a relatively large proportion of animals not culled at the Index test with reactions to Avian tuberculin were found to have Bovine TB in the next 18 months • Ignoring the Avian reaction decreased the number of animals later found to have Bovine TB several fold, but if the Avian reaction is ignored and the use of standard & severe interpretations is unchanged, 5 times as many animals would be culled at the Index test • Although the Avian reaction can be a useful correction for test reactions not due to M. bovis, how the test is implemented could be improved. It may be possible to reduce the potency of Avian tuberculin, or give the Avian reaction less weight when selecting reactors WORK THAT NEEDS TO BE DONE: – A pilot field trial of moderating the effect of reactions to Avian tuberculin when selecting reactors, for example by subtracting only half or threequarters of the Avian reaction from the Bovine reaction – Obtaining reliable data on geographical variation in the prevalence of crossreacting infections, e.g. _Mycobacterium avium_ subsp. _paratuberculosis_ and environmental mycobacteria, so that it may be compared with spatial variation in the reactions to Avian tuberculin – Obtaining comprehensive data for skin tests (VeBus, TB Master, SAM6 etc) to detect differences in Avian effect in TB breakdowns associated with the various molecular types of _M. bovis_
The single intradermal comparative cervical tuberculin (SICCT) test is the primary test used for ... more The single intradermal comparative cervical tuberculin (SICCT) test is the primary test used for surveillance for bovine tuberculosis (bTB) in cattle in Great Britain (GB). The tuberculin used can, with other factors, influence test accuracy. In this analysis, the detection of infected cattle in GB 2005–2009 was compared between SICCT tests using tuberculins manufactured by different manufacturers. Higher rates of reactors (adjusted rate 209 vs 186 per 100,000 tests, P=0.003) and herd bTB incidents (adjusted total breakdown rate 5.1 vs 4.5 per 100 herd-years at risk, P<0.001) were detected using tuberculin manufactured at Weybridge compared with Lelystad. However, confirmation of infection in reactors by postmortem evidence was higher with Lelystad tuberculin (adjusted percent 44.1 vs 47.1, P=0.018). The findings, overall, suggest slightly higher test sensitivity and lower test specificity associated with Weybridge tuberculin compared with Lelystad. Assuming effective adjustment for confounding, the overall impact of tuberculin manufacturing source (2007–2009), was calculated to range somewhere between 315 false positive breakdowns, and 1086 bTB breakdowns missed (624 confirmed) as a result of using Weybridge and Lelystad tuberculin, respectively. However, animals that tested negative to the SICCT were not slaughtered at the time of the tests, so definitive conclusions are not possible.
PLOS Computational Biology 8(10): e1002730.
doi:10.1371/journal.pcbi.1002730, 2012
The number o... more PLOS Computational Biology 8(10): e1002730. doi:10.1371/journal.pcbi.1002730, 2012
The number of cattle herds placed under movement restrictions in Great Britain (GB) due to the suspected presence of bovine tuberculosis (bTB) has progressively increased over the past 25 years despite an intensive and costly test-and-slaughter control program. Around 38% of herds that clear movement restrictions experience a recurrent incident (breakdown) within 24 months, suggesting that infection may be persisting within herds. Reactivity to tuberculin, the basis of diagnostic testing, is dependent on the time from infection. Thus, testing efficiency varies between outbreaks, depending on weight of transmission and cannot be directly estimated. In this paper, we use Approximate Bayesian Computation (ABC) to parameterize two within-herd transmission models within a rigorous inferential framework. Previous within-herd models of bTB have relied on ad-hoc methods of parameterization and used a single model structure (SORI) where animals are assumed to become detectable by testing before they become infectious. We study such a conventional within-herd model of bTB and an alternative model, motivated by recent animal challenge studies, where there is no period of epidemiological latency before animals become infectious (SOR). Under both models we estimate that cattle-to-cattle transmission rates are nonlinearly density dependent. The basic reproductive ratio for our conventional within-herd model, estimated for scenarios with no statutory controls, increases from 1.5 (0.26–4.9; 95% CI) in a herd of 30 cattle up to 4.9 (0.99–14.0) in a herd of 400. Under this model we estimate that 50% (33–67) of recurrent breakdowns in Britain can be attributed to infection missed by tuberculin testing. However this figure falls to 24% (11–42) of recurrent breakdowns under our alternative model. Under both models the estimated extrinsic force of infection increases with the burden of missed infection. Hence, improved herd-level testing is unlikely to reduce recurrence unless this extrinsic infectious pressure is simultaneously addressed.
JOURNAL OF AGRICULTURAL SCIENCE (CAMBRIDGE) 129: 353-366 (1997)
Annual variation in the feeding... more JOURNAL OF AGRICULTURAL SCIENCE (CAMBRIDGE) 129: 353-366 (1997)
Annual variation in the feeding value of barley straw (Hordeum vulgare L. subsp. vulgare) is economically significant in the Mediterranean region. The relationship between the feeding value for sheep of several winter-planted barley cultivars and monthly meteorological data was analysed at Tel Hadya, northwest Syria (mean annual precipitation 330 mm) in 11 years. Indicators of feeding value included contents of neutral detergent fibre, acid detergent fibre and nitrogen (11 years), voluntary straw intake by sheep (10 years), voluntary digestible organic matter intake (9 years), in sacco dry matter loss and lignin content (8 years), in vitro digestibility (7 years), and in vitro gas production (6 years). Monthly meteorological data included total precipitation, mean minimum and mean maximum air temperatures. Conditions likely to decrease grain yield tended to increase the feeding value of straw. Low mean minimum temperature in February, low precipitation in January, February, March and April, and high mean maximum temperature in March, April and May increased one or more indicator of straw feeding value (by both bivariate and multiple regression, P<0.05). Precipitation before January affected grain and straw yield but had little effect on the feeding value of straw. Genotype × year interactions had a meteorological component; the superior feeding value of the straw of locally-adapted cultivars vs. exotic cultivars was only seen in years with cool or wet springs. This has implications for the genetic selection of crops with better straw feeding value. Models based on monthly precipitation and temperature, calibrated for locations in the Mediterranean region, can predict the nutritive value of straw and aid the planning of rations for small ruminants.
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting th... more Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (''whole herd slaughters'' or ''depopulations'') that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
A novel method for estimating specificity of the Single Intradermal Comparative Cervical Tubercul... more A novel method for estimating specificity of the Single Intradermal Comparative Cervical Tuberculin (SICCT) test for bovine tuberculosis (bTB) using surveillance tests results is reported. The specificity of the SICCT test at three cut-offs was estimated from the dates, locations and skinfold measurements of all routine tests carried out in Officially TB Free (OTF) cattle herds in Great Britain (GB) between 2002 and 2008, according to their separation (by distance and time) from known infected (OTF-withdrawn) herds. The proportion of animals that tested positive was constant (P>0.20) when the distance between tested herds and nearest infected herd exceeded 8 km. For standard cut-off, calculated specificity was 99.98 per cent (95 per cent confidence interval ±0.004 per cent), equating to one false positive result per 5000 uninfected animals tested. For severe cut-off it was 99.91 per cent (±0.013 per cent) and for ultrasevere cut-off (selecting all reactors and inconclusive reactors) it was 99.87 per cent (±0.017 per cent). The estimated positive predictive value of the test averaged 91 per cent and varied by regional prevalence. This study provides further evidence of the high specificity of the SICCT test under GB conditions, suggests that over 90 per cent of cattle currently culled using this test in GB were infected, and endorses slaughter of at least these cattle for bTB control.
by Goodchild, A. V., Downs, S. H., Upton, P., Wood, J. L. N., de la Rua-Domenech, R. (2015) Veterinary Record, published online September 2, 2015.
The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of... more The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of cellular immunity (the skin, gamma-interferon and lymphocyte transformation tests). Tests of humoral (antibody) immunity, Mycobacterium bovis PCR probes on early tissue cultures or live cattle specimens, and tests based on &quot;electronic nose&quot; technology have been developed more recently. The key measure of diagnostic test accuracy is the relationship between sensitivity and specificity, which determines the false-positive and false-negative proportions. None of the tests currently available for the diagnosis of bovine TB allow a perfectly accurate determination of the M. bovis infection status of cattle. Although various factors can reduce the sensitivity and specificity of the skin tests, these remain the primary ante mortem diagnostic tools for TB in cattle, providing a cost-effective and reliable means of screening entire cattle populations. Despite the inescapable limitations of existing diagnostic tests, bovine TB has been effectively eradicated from many developed countries and regions with the implementation of sound programmes of regular tuberculin skin testing and removal of reactors, coupled with slaughterhouse surveillance for undetected infections, repeat testing and culling of infected herds, cattle movement restrictions to prevent introduction of infected animals and occasional slaughter of entire herds with intractable breakdowns. This is likely to remain the mainstay of bovine TB control programmes for the foreseeable future. Additionally, newer ancillary in vitro diagnostic assays are now available to TB control programme managers to supplement the skin tests in defined circumstances according to the specific disease situation in each country or region. The strategic deployment of ancillary in vitro tests alongside the primary skin tests has enhanced the detection of M. bovis-infected cattle and reduced the number of animals slaughtered as false positives.
This report, provided by the Animal and Plant Health Agency, summarises the infection status of b... more This report, provided by the Animal and Plant Health Agency, summarises the infection status of bovine TB in cattle in Great Britain from January 1 to December 31, 2013 and describes some of the temporal trends observed over a longer period. It updates the previous annual summary for 2012, also published in the Veterinary Record vol. 174: 600-604 (2014).
Broughan JM, Harris KA, Brouwer A, Downs SH, Goodchild AV, Upton PA, Smith NH. Veterinary Record 176: 326-330 (2015).
Experimental Agriculture 40: pp. 277–294 (2004).
DOI: 10.1017/S0014479704001814
Straws and sto... more Experimental Agriculture 40: pp. 277–294 (2004). DOI: 10.1017/S0014479704001814
Straws and stovers are often called ‘by-products’ of grain production even though they are increasingly important, e.g. for animal feed, thatching, soil improvement, mushroom production and industrial use. As a result, plant breeders, agronomists, economists and animal nutritionists have to pay more attention than before to the total value of crops, i.e. whole plant value in which straws and grain both play a part. This paper reviews literature about the technical potential of breeding and/or management for more or better straw. It then discusses issues of the economic value (EV) and nutritional value (NV) of straw and stovers for livestock feed to guide research and development in cereal breeding and management. It is mainly based on experiences from the Indian subcontinent and semi-arid regions of the Near and Middle East. The paper shows that the quantity and quality of straw produced has changed considerably over recent decades as a result of breeding policies, new cultivation patterns and choice of cultivars. Both EV and NV depend on type of grain, animal production system and access to other feeds. A classification of these factors is provided and suggests that the EV of straw is particularly important in low-input systems with stovers from coarse grains.
Options Méditerranéennes, Série A. Séminaires Méditerranéens; n. 34. Seminar of the FAO-CIHEAM N... more Options Méditerranéennes, Série A. Séminaires Méditerranéens; n. 34. Seminar of the FAO-CIHEAM Network of Cooperative Research on Sheep and Goats, Subnetwork on Nutrition, 24-26 Oct 1996, Rabat (Morocco). Zaragoza : CIHEAM, 1997. p. 87-92.
In sheep fed diets containing ad libitum barley straw, body weight change is closely correlated with straw intake. We are finding that it is more effective to select genotypes for straw intake using calibrated indirect tests than by conducting intake trials with sheep. Not only are the tests cheaper, but the test results are more heritable, even when their genotypic correlationw ith intake is allowed for. Of the tests, Near Infrared Reflectance Spectroscopy is the most effective, followed by in sacco dry matter loss, acid detergent fibre, pair-preference tests in sheep, and in vitro gas production with rumen fluid.
PLOS One 7(8): e43217. doi:10.1371/journal.pone.0043217.
Bovine tuberculosis (bTB) is one of th... more PLOS One 7(8): e43217. doi:10.1371/journal.pone.0043217.
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (‘‘whole herd slaughters’’ or ‘‘depopulations’’) that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
Veterinary Record 174: 600-604 (2014). doi: 10.1136/vr.g3644
This report, provided by the AHVLA... more Veterinary Record 174: 600-604 (2014). doi: 10.1136/vr.g3644
This report, provided by the AHVLA, summarises the infection status of bovine tuberculosis (TB) in cattle in Great Britain from January 1 to December 31, 2012 and describes some of the temporal trends observed over a longer period. The AHVLA intends to produce similar reports for future years to provide a concise summary of how the situation is developing.
Annual conference of the Society for Veterinary Epidemiology and Preventive Medicine, Espoo, Hels... more Annual conference of the Society for Veterinary Epidemiology and Preventive Medicine, Espoo, Helsinki, Finland 2007 (poster).
Since herd sizes have been increasing in the last 40 years and the probability of a herd being infected increases with herd size, could that explain the rise in bovine TB? However, - The bovine TB rise happened c. 20 years after the increase in average herd size - The probability of an individual animal being confirmed with TB doesn't vary with herd size But herd size is still very important: - Herd size increases the probability and duration of bovine TB incidents. This affects the economic and animal welfare problems caused bu bovine TB.
Annual Conference of the Society for Veterinary Epidemiology and Peventive Medicine, Edinburgh 20... more Annual Conference of the Society for Veterinary Epidemiology and Peventive Medicine, Edinburgh 2012 (poster)
An analysis of the data used here by stepwise logistic regression using eight types of covariate confirmed the following results • Subtracting the Avian reaction from the Bovine reaction when selecting TB reactors may not always be the most accurate way to detect infected animals • In particular, a relatively large proportion of animals not culled at the Index test with reactions to Avian tuberculin were found to have Bovine TB in the next 18 months • Ignoring the Avian reaction decreased the number of animals later found to have Bovine TB several fold, but if the Avian reaction is ignored and the use of standard & severe interpretations is unchanged, 5 times as many animals would be culled at the Index test • Although the Avian reaction can be a useful correction for test reactions not due to M. bovis, how the test is implemented could be improved. It may be possible to reduce the potency of Avian tuberculin, or give the Avian reaction less weight when selecting reactors WORK THAT NEEDS TO BE DONE: – A pilot field trial of moderating the effect of reactions to Avian tuberculin when selecting reactors, for example by subtracting only half or threequarters of the Avian reaction from the Bovine reaction – Obtaining reliable data on geographical variation in the prevalence of crossreacting infections, e.g. _Mycobacterium avium_ subsp. _paratuberculosis_ and environmental mycobacteria, so that it may be compared with spatial variation in the reactions to Avian tuberculin – Obtaining comprehensive data for skin tests (VeBus, TB Master, SAM6 etc) to detect differences in Avian effect in TB breakdowns associated with the various molecular types of _M. bovis_
The single intradermal comparative cervical tuberculin (SICCT) test is the primary test used for ... more The single intradermal comparative cervical tuberculin (SICCT) test is the primary test used for surveillance for bovine tuberculosis (bTB) in cattle in Great Britain (GB). The tuberculin used can, with other factors, influence test accuracy. In this analysis, the detection of infected cattle in GB 2005–2009 was compared between SICCT tests using tuberculins manufactured by different manufacturers. Higher rates of reactors (adjusted rate 209 vs 186 per 100,000 tests, P=0.003) and herd bTB incidents (adjusted total breakdown rate 5.1 vs 4.5 per 100 herd-years at risk, P<0.001) were detected using tuberculin manufactured at Weybridge compared with Lelystad. However, confirmation of infection in reactors by postmortem evidence was higher with Lelystad tuberculin (adjusted percent 44.1 vs 47.1, P=0.018). The findings, overall, suggest slightly higher test sensitivity and lower test specificity associated with Weybridge tuberculin compared with Lelystad. Assuming effective adjustment for confounding, the overall impact of tuberculin manufacturing source (2007–2009), was calculated to range somewhere between 315 false positive breakdowns, and 1086 bTB breakdowns missed (624 confirmed) as a result of using Weybridge and Lelystad tuberculin, respectively. However, animals that tested negative to the SICCT were not slaughtered at the time of the tests, so definitive conclusions are not possible.
PLOS Computational Biology 8(10): e1002730.
doi:10.1371/journal.pcbi.1002730, 2012
The number o... more PLOS Computational Biology 8(10): e1002730. doi:10.1371/journal.pcbi.1002730, 2012
The number of cattle herds placed under movement restrictions in Great Britain (GB) due to the suspected presence of bovine tuberculosis (bTB) has progressively increased over the past 25 years despite an intensive and costly test-and-slaughter control program. Around 38% of herds that clear movement restrictions experience a recurrent incident (breakdown) within 24 months, suggesting that infection may be persisting within herds. Reactivity to tuberculin, the basis of diagnostic testing, is dependent on the time from infection. Thus, testing efficiency varies between outbreaks, depending on weight of transmission and cannot be directly estimated. In this paper, we use Approximate Bayesian Computation (ABC) to parameterize two within-herd transmission models within a rigorous inferential framework. Previous within-herd models of bTB have relied on ad-hoc methods of parameterization and used a single model structure (SORI) where animals are assumed to become detectable by testing before they become infectious. We study such a conventional within-herd model of bTB and an alternative model, motivated by recent animal challenge studies, where there is no period of epidemiological latency before animals become infectious (SOR). Under both models we estimate that cattle-to-cattle transmission rates are nonlinearly density dependent. The basic reproductive ratio for our conventional within-herd model, estimated for scenarios with no statutory controls, increases from 1.5 (0.26–4.9; 95% CI) in a herd of 30 cattle up to 4.9 (0.99–14.0) in a herd of 400. Under this model we estimate that 50% (33–67) of recurrent breakdowns in Britain can be attributed to infection missed by tuberculin testing. However this figure falls to 24% (11–42) of recurrent breakdowns under our alternative model. Under both models the estimated extrinsic force of infection increases with the burden of missed infection. Hence, improved herd-level testing is unlikely to reduce recurrence unless this extrinsic infectious pressure is simultaneously addressed.
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Annual variation in the feeding value of barley straw (Hordeum vulgare L. subsp. vulgare) is economically significant in the Mediterranean region. The relationship between the feeding value for sheep of several winter-planted barley cultivars and monthly meteorological data was analysed at Tel Hadya, northwest Syria (mean annual precipitation 330 mm) in 11 years. Indicators of feeding value included contents of neutral detergent fibre, acid detergent fibre and nitrogen (11 years), voluntary straw intake by sheep (10 years), voluntary digestible organic matter intake (9 years), in sacco dry matter loss and lignin content (8 years), in vitro digestibility (7 years), and in vitro gas production (6 years). Monthly meteorological data included total precipitation, mean minimum and mean maximum air temperatures.
Conditions likely to decrease grain yield tended to increase the feeding value of straw. Low mean minimum temperature in February, low precipitation in January, February, March and April, and high mean maximum temperature in March, April and May increased one or more indicator of straw feeding value (by both bivariate and multiple regression, P<0.05). Precipitation before January affected grain and straw yield but had little effect on the feeding value of straw.
Genotype × year interactions had a meteorological component; the superior feeding value of the straw of locally-adapted cultivars vs. exotic cultivars was only seen in years with cool or wet springs. This has implications for the genetic selection of crops with better straw feeding value.
Models based on monthly precipitation and temperature, calibrated for locations in the Mediterranean region, can predict the nutritive value of straw and aid the planning of rations for small ruminants.
by Goodchild, A. V., Downs, S. H., Upton, P., Wood, J. L. N., de la Rua-Domenech, R. (2015) Veterinary Record, published online September 2, 2015.
Updated information and services can be found at: http://veterinaryrecord.bmj.com/content/early/2015/09/02/vr.102961
Broughan JM, Harris KA, Brouwer A, Downs SH, Goodchild AV, Upton PA, Smith NH. Veterinary Record 176: 326-330 (2015).
DOI: 10.1017/S0014479704001814
Straws and stovers are often called ‘by-products’ of grain production even though they are increasingly important, e.g. for animal feed, thatching, soil improvement, mushroom production and industrial use. As a result, plant breeders, agronomists, economists and animal nutritionists have to pay more attention than before to the total value of crops, i.e. whole plant value in which straws and grain both play a part. This paper reviews literature about the technical potential of breeding and/or management for more or better straw. It then discusses issues of the economic value (EV) and nutritional value (NV) of straw and stovers for livestock feed to guide research and development in cereal breeding and management. It is mainly based on experiences from the Indian subcontinent and semi-arid regions of the Near and Middle East. The paper shows that the quantity and quality of straw produced has changed considerably over recent decades as a result of breeding policies, new cultivation patterns and choice of cultivars. Both EV and NV depend on type of grain, animal production system and access to other feeds. A classification of these factors is provided and suggests that the EV of straw is particularly important in low-input systems with
stovers from coarse grains.
In sheep fed diets containing ad libitum barley straw, body weight change is closely correlated with straw intake. We are finding that it is more effective to select genotypes for straw intake using calibrated indirect tests than by conducting intake trials with sheep. Not only are the tests cheaper, but the test results are more heritable, even when their genotypic correlationw ith intake is allowed for. Of the tests, Near Infrared Reflectance Spectroscopy is the most effective, followed by in sacco dry matter loss, acid detergent fibre, pair-preference tests in sheep, and in vitro gas production with rumen fluid.
KEYWORDS: Laboratory methods / nutritive value / barley straw / sheep
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (‘‘whole herd slaughters’’ or ‘‘depopulations’’) that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible
interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than
those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
This report, provided by the AHVLA, summarises the infection status of bovine tuberculosis (TB) in cattle in Great Britain from January 1 to December 31, 2012 and describes some of the temporal trends observed over a longer period. The AHVLA intends to produce similar reports for future years to provide a concise summary of how the situation is developing.
Since herd sizes have been increasing in the last 40 years and the probability of a herd being infected increases with herd size, could that explain the rise in bovine TB?
However,
- The bovine TB rise happened c. 20 years after the increase in average herd size
- The probability of an individual animal being confirmed with TB doesn't vary with herd size
But herd size is still very important:
- Herd size increases the probability and duration of bovine TB incidents. This affects the economic and animal welfare problems caused bu bovine TB.
An analysis of the data used here by stepwise logistic regression using eight types of covariate confirmed the following results
• Subtracting the Avian reaction from the Bovine reaction when selecting TB reactors may not always be the most accurate way to detect infected animals
• In particular, a relatively large proportion of animals not culled at the Index test with reactions to Avian tuberculin were found to have Bovine TB in the next 18 months
• Ignoring the Avian reaction decreased the number of animals later found to have Bovine TB several fold, but if the Avian reaction is ignored and the use of standard & severe interpretations is unchanged, 5 times as many animals would be culled at the Index test
• Although the Avian reaction can be a useful correction for test reactions not due to M. bovis, how the test is implemented could be improved. It may be possible to reduce the potency of Avian tuberculin, or give the Avian reaction less weight when selecting reactors
WORK THAT NEEDS TO BE DONE:
– A pilot field trial of moderating the effect of reactions to Avian tuberculin when selecting reactors, for example by subtracting only half or threequarters of the Avian reaction from the Bovine reaction
– Obtaining reliable data on geographical variation in the prevalence of crossreacting infections, e.g. _Mycobacterium avium_ subsp. _paratuberculosis_ and environmental mycobacteria, so that it may be compared with spatial variation
in the reactions to Avian tuberculin
– Obtaining comprehensive data for skin tests (VeBus, TB Master, SAM6 etc) to detect differences in Avian effect in TB breakdowns associated with the various molecular types of _M. bovis_
used can, with other factors, influence test accuracy. In this analysis, the detection of infected cattle in GB 2005–2009 was compared between SICCT tests using tuberculins manufactured by different manufacturers. Higher rates of reactors (adjusted rate 209 vs 186 per 100,000 tests, P=0.003) and herd bTB incidents (adjusted total breakdown rate 5.1 vs 4.5 per 100 herd-years at risk, P<0.001) were detected using tuberculin manufactured at Weybridge compared with Lelystad. However, confirmation of infection in reactors by postmortem evidence was higher with Lelystad tuberculin (adjusted percent 44.1 vs 47.1, P=0.018). The findings, overall, suggest slightly higher test sensitivity and lower test specificity associated with Weybridge tuberculin compared with Lelystad. Assuming effective adjustment for confounding, the overall impact of tuberculin manufacturing source (2007–2009), was
calculated to range somewhere between 315 false positive breakdowns, and 1086 bTB breakdowns missed (624 confirmed) as a result of using Weybridge and Lelystad tuberculin, respectively. However, animals that tested negative to the SICCT were not slaughtered at the time of the tests, so definitive conclusions are not possible.
doi:10.1371/journal.pcbi.1002730, 2012
The number of cattle herds placed under movement restrictions in Great Britain (GB) due to the suspected presence of bovine tuberculosis (bTB) has progressively increased over the past 25 years despite an intensive and costly test-and-slaughter control program. Around 38% of herds that clear movement restrictions experience a recurrent incident (breakdown) within 24 months, suggesting that infection may be persisting within herds. Reactivity to tuberculin, the basis of diagnostic testing, is dependent on the time from infection. Thus, testing efficiency varies between outbreaks, depending on weight of transmission and cannot be directly estimated. In this paper, we use Approximate Bayesian Computation (ABC) to parameterize two within-herd transmission models within a rigorous inferential framework. Previous within-herd models of bTB have relied on ad-hoc methods of parameterization and used a single model structure (SORI) where animals are assumed to become detectable by testing before they become infectious. We study such a conventional within-herd model of bTB and an alternative model, motivated by recent animal challenge studies, where there is no period of epidemiological latency before animals become infectious (SOR). Under both models we estimate that cattle-to-cattle transmission rates are nonlinearly density dependent. The basic reproductive ratio for our conventional within-herd model, estimated for scenarios with no statutory controls, increases from 1.5 (0.26–4.9; 95% CI) in a herd of 30 cattle up to 4.9 (0.99–14.0) in a herd of 400. Under this model we estimate that 50% (33–67) of recurrent breakdowns in Britain can be attributed to infection missed by tuberculin testing. However this figure falls to 24% (11–42) of recurrent breakdowns under our alternative model. Under both models the estimated extrinsic force of infection increases with the burden of missed infection. Hence, improved herd-level testing is unlikely to reduce recurrence unless this extrinsic infectious pressure is simultaneously addressed.
Annual variation in the feeding value of barley straw (Hordeum vulgare L. subsp. vulgare) is economically significant in the Mediterranean region. The relationship between the feeding value for sheep of several winter-planted barley cultivars and monthly meteorological data was analysed at Tel Hadya, northwest Syria (mean annual precipitation 330 mm) in 11 years. Indicators of feeding value included contents of neutral detergent fibre, acid detergent fibre and nitrogen (11 years), voluntary straw intake by sheep (10 years), voluntary digestible organic matter intake (9 years), in sacco dry matter loss and lignin content (8 years), in vitro digestibility (7 years), and in vitro gas production (6 years). Monthly meteorological data included total precipitation, mean minimum and mean maximum air temperatures.
Conditions likely to decrease grain yield tended to increase the feeding value of straw. Low mean minimum temperature in February, low precipitation in January, February, March and April, and high mean maximum temperature in March, April and May increased one or more indicator of straw feeding value (by both bivariate and multiple regression, P<0.05). Precipitation before January affected grain and straw yield but had little effect on the feeding value of straw.
Genotype × year interactions had a meteorological component; the superior feeding value of the straw of locally-adapted cultivars vs. exotic cultivars was only seen in years with cool or wet springs. This has implications for the genetic selection of crops with better straw feeding value.
Models based on monthly precipitation and temperature, calibrated for locations in the Mediterranean region, can predict the nutritive value of straw and aid the planning of rations for small ruminants.
by Goodchild, A. V., Downs, S. H., Upton, P., Wood, J. L. N., de la Rua-Domenech, R. (2015) Veterinary Record, published online September 2, 2015.
Updated information and services can be found at: http://veterinaryrecord.bmj.com/content/early/2015/09/02/vr.102961
Broughan JM, Harris KA, Brouwer A, Downs SH, Goodchild AV, Upton PA, Smith NH. Veterinary Record 176: 326-330 (2015).
DOI: 10.1017/S0014479704001814
Straws and stovers are often called ‘by-products’ of grain production even though they are increasingly important, e.g. for animal feed, thatching, soil improvement, mushroom production and industrial use. As a result, plant breeders, agronomists, economists and animal nutritionists have to pay more attention than before to the total value of crops, i.e. whole plant value in which straws and grain both play a part. This paper reviews literature about the technical potential of breeding and/or management for more or better straw. It then discusses issues of the economic value (EV) and nutritional value (NV) of straw and stovers for livestock feed to guide research and development in cereal breeding and management. It is mainly based on experiences from the Indian subcontinent and semi-arid regions of the Near and Middle East. The paper shows that the quantity and quality of straw produced has changed considerably over recent decades as a result of breeding policies, new cultivation patterns and choice of cultivars. Both EV and NV depend on type of grain, animal production system and access to other feeds. A classification of these factors is provided and suggests that the EV of straw is particularly important in low-input systems with
stovers from coarse grains.
In sheep fed diets containing ad libitum barley straw, body weight change is closely correlated with straw intake. We are finding that it is more effective to select genotypes for straw intake using calibrated indirect tests than by conducting intake trials with sheep. Not only are the tests cheaper, but the test results are more heritable, even when their genotypic correlationw ith intake is allowed for. Of the tests, Near Infrared Reflectance Spectroscopy is the most effective, followed by in sacco dry matter loss, acid detergent fibre, pair-preference tests in sheep, and in vitro gas production with rumen fluid.
KEYWORDS: Laboratory methods / nutritive value / barley straw / sheep
Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (‘‘whole herd slaughters’’ or ‘‘depopulations’’) that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible
interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than
those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.
This report, provided by the AHVLA, summarises the infection status of bovine tuberculosis (TB) in cattle in Great Britain from January 1 to December 31, 2012 and describes some of the temporal trends observed over a longer period. The AHVLA intends to produce similar reports for future years to provide a concise summary of how the situation is developing.
Since herd sizes have been increasing in the last 40 years and the probability of a herd being infected increases with herd size, could that explain the rise in bovine TB?
However,
- The bovine TB rise happened c. 20 years after the increase in average herd size
- The probability of an individual animal being confirmed with TB doesn't vary with herd size
But herd size is still very important:
- Herd size increases the probability and duration of bovine TB incidents. This affects the economic and animal welfare problems caused bu bovine TB.
An analysis of the data used here by stepwise logistic regression using eight types of covariate confirmed the following results
• Subtracting the Avian reaction from the Bovine reaction when selecting TB reactors may not always be the most accurate way to detect infected animals
• In particular, a relatively large proportion of animals not culled at the Index test with reactions to Avian tuberculin were found to have Bovine TB in the next 18 months
• Ignoring the Avian reaction decreased the number of animals later found to have Bovine TB several fold, but if the Avian reaction is ignored and the use of standard & severe interpretations is unchanged, 5 times as many animals would be culled at the Index test
• Although the Avian reaction can be a useful correction for test reactions not due to M. bovis, how the test is implemented could be improved. It may be possible to reduce the potency of Avian tuberculin, or give the Avian reaction less weight when selecting reactors
WORK THAT NEEDS TO BE DONE:
– A pilot field trial of moderating the effect of reactions to Avian tuberculin when selecting reactors, for example by subtracting only half or threequarters of the Avian reaction from the Bovine reaction
– Obtaining reliable data on geographical variation in the prevalence of crossreacting infections, e.g. _Mycobacterium avium_ subsp. _paratuberculosis_ and environmental mycobacteria, so that it may be compared with spatial variation
in the reactions to Avian tuberculin
– Obtaining comprehensive data for skin tests (VeBus, TB Master, SAM6 etc) to detect differences in Avian effect in TB breakdowns associated with the various molecular types of _M. bovis_
used can, with other factors, influence test accuracy. In this analysis, the detection of infected cattle in GB 2005–2009 was compared between SICCT tests using tuberculins manufactured by different manufacturers. Higher rates of reactors (adjusted rate 209 vs 186 per 100,000 tests, P=0.003) and herd bTB incidents (adjusted total breakdown rate 5.1 vs 4.5 per 100 herd-years at risk, P<0.001) were detected using tuberculin manufactured at Weybridge compared with Lelystad. However, confirmation of infection in reactors by postmortem evidence was higher with Lelystad tuberculin (adjusted percent 44.1 vs 47.1, P=0.018). The findings, overall, suggest slightly higher test sensitivity and lower test specificity associated with Weybridge tuberculin compared with Lelystad. Assuming effective adjustment for confounding, the overall impact of tuberculin manufacturing source (2007–2009), was
calculated to range somewhere between 315 false positive breakdowns, and 1086 bTB breakdowns missed (624 confirmed) as a result of using Weybridge and Lelystad tuberculin, respectively. However, animals that tested negative to the SICCT were not slaughtered at the time of the tests, so definitive conclusions are not possible.
doi:10.1371/journal.pcbi.1002730, 2012
The number of cattle herds placed under movement restrictions in Great Britain (GB) due to the suspected presence of bovine tuberculosis (bTB) has progressively increased over the past 25 years despite an intensive and costly test-and-slaughter control program. Around 38% of herds that clear movement restrictions experience a recurrent incident (breakdown) within 24 months, suggesting that infection may be persisting within herds. Reactivity to tuberculin, the basis of diagnostic testing, is dependent on the time from infection. Thus, testing efficiency varies between outbreaks, depending on weight of transmission and cannot be directly estimated. In this paper, we use Approximate Bayesian Computation (ABC) to parameterize two within-herd transmission models within a rigorous inferential framework. Previous within-herd models of bTB have relied on ad-hoc methods of parameterization and used a single model structure (SORI) where animals are assumed to become detectable by testing before they become infectious. We study such a conventional within-herd model of bTB and an alternative model, motivated by recent animal challenge studies, where there is no period of epidemiological latency before animals become infectious (SOR). Under both models we estimate that cattle-to-cattle transmission rates are nonlinearly density dependent. The basic reproductive ratio for our conventional within-herd model, estimated for scenarios with no statutory controls, increases from 1.5 (0.26–4.9; 95% CI) in a herd of 30 cattle up to 4.9 (0.99–14.0) in a herd of 400. Under this model we estimate that 50% (33–67) of recurrent breakdowns in Britain can be attributed to infection missed by tuberculin testing. However this figure falls to 24% (11–42) of recurrent breakdowns under our alternative model. Under both models the estimated extrinsic force of infection increases with the burden of missed infection. Hence, improved herd-level testing is unlikely to reduce recurrence unless this extrinsic infectious pressure is simultaneously addressed.