ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of... more ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of LH during the postpartum period in beef cows. In addition, the influence of exogenous administration of low concentrations of estradiol on LH secretion during the postpartum period was evaluated. Twelve mature cows were randomly assigned before parturition to one of three treatments. Four intact cows were used as controls (INT). Eight cows were ovariectomized within the first 7 days following parturition. Four of these cows received a silastic 17β-estradiol implant subcutaneously at the time of ovariectomy (OVX-E); the remaining four cows received no further treatment (OVX). All cows were allowed to nurse one calf for 30 min daily between 1200 and 1230 hours for the duration of the experiment. Blood samples were collected at 12 min intervals for 6 hr before and 6 hr after suckling on days 9, 30, 44 and 58 postpartum. Mean interval (mean ± SE) to the first increase in peripheral progesterone concentrations indicative of the onset of ovarian luteal activity was detected in INT cows 37 ± 4.9 days postpartum. An acute effect of suckling on LH secretion did not occur in INT and OVX cows but mean LH concentrations were reduced in OVX-E cows following suckling on days 44 and 58. Mean LH concentrations remained low in INT cows; whereas, in OVX and OVX-E cows LH concentrations increased linearly (P<0.05) as the interval from time of ovariectomy increased. Cows in the OVX-E group had a higher mean concentration of LH than cows in the OVX group at 30, 44 and 58 days postpartum (P<0.05). Frequency of LH pulses did not differ between cows in the OVX and OVX-E groups at any period. Data from this experiment support the concept that suckling is acting in a chronic fashion to inhibit LH secretion during the postpartum period. In the absence of ovaries, chronic administration of exogenous estradiol in low concentrations has a positive effect on secretion of LH in the postpartum cow.
To examine effects of norgestomet pretreatment on development of follicles and their response to ... more To examine effects of norgestomet pretreatment on development of follicles and their response to administration of gonadotropin releasing hormone (GnRH), 45 pluriparous suckled beef cows were assigned at random to receive a 6-mg implant of norgestomet for 9 d (inserted 24 d postpartum) or serve as untreated controls. Ovaries were obtained 48 h after removal of implants or 10 to 11 or 20 to 22 h after im administration of 150 micrograms GnRH at 48 h after removal of the implant. The largest follicle (F1) and all follicles within 3 mm in diameter of the F1 were dissected from the ovaries. Theca, granulosa and follicular fluid were separated and assayed for steroids and prostaglandins. Diameters and weights of F1 and weights of follicular components remained unchanged in control cows, but increased by 10 h and declined by 20 h in norgestomet-pretreated cows (treatment X time, quadratic, P less than .05). Ovarian volume and numbers of follicles at the surface of the ovary did not differ...
Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses ... more Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses to induction of superovulation were studied in old (greater than 12 yr) and young (5 to 7 yr) lactating beef cows. Seventeen cows (8 old and 9 young) received a 6-mg N ear implant on d 4 or 5 of the cycle (d 0 = estrus); the remaining 17 cows (9 old and 8 young) served as untreated controls (C). All animals were treated with 38 mg of porcine follicle-stimulating hormone (FSH-P) in decreasing dosages over a 4.5-d period beginning on d 10 or 11. Regression of the corpus luteum was induced with injections of PGF2 alpha at 0800 and 2000 on d 4 of FSH-P treatment; implants were removed at the second injection of PGF2 alpha. Cows were inseminated artificially 12 and 24 h after onset of estrus. Embryos were collected on d 7 or 8 postinsemination. Blood samples were obtained daily at 0800 from 2 d prior to initiation of treatment with FSH-P until collection of embryos. An additional sample was c...
The effect of implants of estradiol on initiation of ovarian cycles postpartum was studied in 201... more The effect of implants of estradiol on initiation of ovarian cycles postpartum was studied in 201 anestrous beef cows. Cows from four farms were used over a 2-yr period in a 2 x 3 factorial arrangement of treatments with estradiol implants and stage postpartum as main effects. Cows were assigned at random within date of calving within farm to receive an ear implant containing estradiol-17 beta (24 mg) for 21 d or to serve as controls. Stages postpartum at implantation were divided into less than or equal to 25, 26 to 39, and greater than or equal to 40 d, three stages that should reflect potential changes in hypothalmic-hypophysial sensitivity to estradiol. Blood samples for determination of progesterone were obtained and rectal examinations of the ovaries performed at implant insertion, 14 d after insertion, at implant removal (d 21), and 14 d after removal (d 35) to assess ovulatory response to treatment. Circulating concentrations of estradiol on d 14 of treatment averaged 3.2 +/...
Defining a common agenda to improve livestock contribution for poverty reduction in Latin America... more Defining a common agenda to improve livestock contribution for poverty reduction in Latin America and the Caribbean. ABSTRACT. The continuing prevalence of poverty and the existence of food insecurity are two of the major risk that threaten the development and stability of countries. Livestock has the possibility to contribute to the sustainable solution of both. In order to achieve this we must: a) Improve both the contribution of livestock to the national GDP and to individual family and producers incomes; b) Work to change the existing popular views around animal production and to reduce any possible impacts of animals to the environment and health; c) Improve the articulation and integration of value chains; d) Improve public policies in order to create an enabling environment for the activity and investment; and e) To bridge the distance between the agricultural innovation systems and the true needs of livestock and all the actors in the value chains. It is proposed that ALPA s...
Two experiments were designed to examine whether hormonal profiles were related to luteal life sp... more Two experiments were designed to examine whether hormonal profiles were related to luteal life span in pluriparous postpartum anestrous beef cows. Cows (Exp. 1, n = 34; Exp. 2, n = 23) received norgestomet (N) for 9 d or served as controls (C). Each cow received 1,000 IU human chorionic gonadotropin (hCG) 48 h after removal of N (d 0). Blood samples collected every 15 min for 8 h on d -5, 3 and 5 (Exp. 1) or on d -10 and -1 (Exp. 2) were assayed for luteinizing hormone (LH) and follicle stimulating hormone (FSH). Cortisol was determined in hourly samples collected on d -5 and in samples collected every 2 min during suckling on the same day (Exp. 1). Concentrations of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) were determined in samples collected at 15-min intervals for 2 h on d -5, 3, 5 and 10 (Exp. 1). Estradiol-17 beta was measured in samples collected on d -5 (Exp. 1) or on d -10 and -1 (Exp. 2). Life span of induced corpora lutea was longer (P less than .05) in N than C cows. Perce...
There is evidence that the dose of PGF(2)alpha generally used to synchronize estrus (25 mg) is hi... more There is evidence that the dose of PGF(2)alpha generally used to synchronize estrus (25 mg) is higher than required to induce luteolysis in cattle. To investigate this, 98 Holstein cows from three farms were assigned at random within farm to be treated with a single dose of 25 mg (n=33), 17.5 mg (n=33) or 10 mg (n=32) of PGF(2)alpha on Day 10+/-0.5 (mean +/- SEM) of the estrous cycle. Statistical analyses were conducted using analyses of variance and Chisquare test. Only 59.3% of the cows treated with 10 mg of PGF(2)alpha were detected in estrus compared with 72.7 and 78.7% of the cows treated with 17.5 and 25.0 mg doses, respectively (P>0.05). There were no differences (P>0.05) in pregnancy rates at the first service (40.0, 66.6 and 50.0% for 25, 17.5 and 10 mg, respectively). Concentrations of progesterone in blood were different (P<0.05) for cows treated with 10 mg compared with those of cows treated with 17.5 or 25 mg of PGF(2)alpha. The pattern of changes in progesterone concentrations between the last two groups was not different, and progesterone concentrations of less than 1 ng/ml of serum were observed within the first 36 h post PGF(2)alpha administration. In cows treated with 10-mg dose of PGF(2)alpha, concentrations of progesterone declined during the first 24 h, however, by the end of the experimental period, they were not different to pretreatment concentrations (treatment x time; P<0.05). It is suggested that reducing the dose of PGF(2)alpha from 25 to 17.5 mg do not affect estrus response or pregnancy rate in Holstein cows.
Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), proge... more Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone (P4) and estradiol-17 beta (E2) during an estrous cycle were compared between 15 lactating beef cows 5 to 7 years of age (young) and 15 cows greater than or equal to 12 years of age (old). Length of estrous cycle did not differ between young and old cows (P = .06). No differences due to age were found for LH. Patterns of concentrations of P4 during the first 15 days of the cycle, of FSH during days 6 through 12 and of E2 during the follicular phase differed with age (P less than .05). An earlier (P less than .025) midcycle elevation of FSH was associated with an earlier rise and greater concentration of E2 (P less than .05) during the follicular phase in old than in young cows. Differences in FSH and P4, although subtle, were consistent with an earlier or more advanced follicular development in old cows, leading to greater secretion of E2 from the preovulatory follicle.
... Intact Red Angus x Hereford heifers in the same herd reached puberty at 384 + 10 days (n6) in... more ... Intact Red Angus x Hereford heifers in the same herd reached puberty at 384 + 10 days (n6) in 1981, and at 410 + 7 (n=6) days in 1984. ... J Anim Sci 47:235240, 1978. 17. Nett TM, Crowder ME, Moss GE, Duello TM. GnRHreceptor interaction. ...
ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of... more ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of LH during the postpartum period in beef cows. In addition, the influence of exogenous administration of low concentrations of estradiol on LH secretion during the postpartum period was evaluated. Twelve mature cows were randomly assigned before parturition to one of three treatments. Four intact cows were used as controls (INT). Eight cows were ovariectomized within the first 7 days following parturition. Four of these cows received a silastic 17β-estradiol implant subcutaneously at the time of ovariectomy (OVX-E); the remaining four cows received no further treatment (OVX). All cows were allowed to nurse one calf for 30 min daily between 1200 and 1230 hours for the duration of the experiment. Blood samples were collected at 12 min intervals for 6 hr before and 6 hr after suckling on days 9, 30, 44 and 58 postpartum. Mean interval (mean ± SE) to the first increase in peripheral progesterone concentrations indicative of the onset of ovarian luteal activity was detected in INT cows 37 ± 4.9 days postpartum. An acute effect of suckling on LH secretion did not occur in INT and OVX cows but mean LH concentrations were reduced in OVX-E cows following suckling on days 44 and 58. Mean LH concentrations remained low in INT cows; whereas, in OVX and OVX-E cows LH concentrations increased linearly (P<0.05) as the interval from time of ovariectomy increased. Cows in the OVX-E group had a higher mean concentration of LH than cows in the OVX group at 30, 44 and 58 days postpartum (P<0.05). Frequency of LH pulses did not differ between cows in the OVX and OVX-E groups at any period. Data from this experiment support the concept that suckling is acting in a chronic fashion to inhibit LH secretion during the postpartum period. In the absence of ovaries, chronic administration of exogenous estradiol in low concentrations has a positive effect on secretion of LH in the postpartum cow.
ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of... more ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of LH during the postpartum period in beef cows. In addition, the influence of exogenous administration of low concentrations of estradiol on LH secretion during the postpartum period was evaluated. Twelve mature cows were randomly assigned before parturition to one of three treatments. Four intact cows were used as controls (INT). Eight cows were ovariectomized within the first 7 days following parturition. Four of these cows received a silastic 17β-estradiol implant subcutaneously at the time of ovariectomy (OVX-E); the remaining four cows received no further treatment (OVX). All cows were allowed to nurse one calf for 30 min daily between 1200 and 1230 hours for the duration of the experiment. Blood samples were collected at 12 min intervals for 6 hr before and 6 hr after suckling on days 9, 30, 44 and 58 postpartum. Mean interval (mean ± SE) to the first increase in peripheral progesterone concentrations indicative of the onset of ovarian luteal activity was detected in INT cows 37 ± 4.9 days postpartum. An acute effect of suckling on LH secretion did not occur in INT and OVX cows but mean LH concentrations were reduced in OVX-E cows following suckling on days 44 and 58. Mean LH concentrations remained low in INT cows; whereas, in OVX and OVX-E cows LH concentrations increased linearly (P<0.05) as the interval from time of ovariectomy increased. Cows in the OVX-E group had a higher mean concentration of LH than cows in the OVX group at 30, 44 and 58 days postpartum (P<0.05). Frequency of LH pulses did not differ between cows in the OVX and OVX-E groups at any period. Data from this experiment support the concept that suckling is acting in a chronic fashion to inhibit LH secretion during the postpartum period. In the absence of ovaries, chronic administration of exogenous estradiol in low concentrations has a positive effect on secretion of LH in the postpartum cow.
To examine effects of norgestomet pretreatment on development of follicles and their response to ... more To examine effects of norgestomet pretreatment on development of follicles and their response to administration of gonadotropin releasing hormone (GnRH), 45 pluriparous suckled beef cows were assigned at random to receive a 6-mg implant of norgestomet for 9 d (inserted 24 d postpartum) or serve as untreated controls. Ovaries were obtained 48 h after removal of implants or 10 to 11 or 20 to 22 h after im administration of 150 micrograms GnRH at 48 h after removal of the implant. The largest follicle (F1) and all follicles within 3 mm in diameter of the F1 were dissected from the ovaries. Theca, granulosa and follicular fluid were separated and assayed for steroids and prostaglandins. Diameters and weights of F1 and weights of follicular components remained unchanged in control cows, but increased by 10 h and declined by 20 h in norgestomet-pretreated cows (treatment X time, quadratic, P less than .05). Ovarian volume and numbers of follicles at the surface of the ovary did not differ...
Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses ... more Effects of age of cow and a norgestomet (N) implant on number of embryos and endocrine responses to induction of superovulation were studied in old (greater than 12 yr) and young (5 to 7 yr) lactating beef cows. Seventeen cows (8 old and 9 young) received a 6-mg N ear implant on d 4 or 5 of the cycle (d 0 = estrus); the remaining 17 cows (9 old and 8 young) served as untreated controls (C). All animals were treated with 38 mg of porcine follicle-stimulating hormone (FSH-P) in decreasing dosages over a 4.5-d period beginning on d 10 or 11. Regression of the corpus luteum was induced with injections of PGF2 alpha at 0800 and 2000 on d 4 of FSH-P treatment; implants were removed at the second injection of PGF2 alpha. Cows were inseminated artificially 12 and 24 h after onset of estrus. Embryos were collected on d 7 or 8 postinsemination. Blood samples were obtained daily at 0800 from 2 d prior to initiation of treatment with FSH-P until collection of embryos. An additional sample was c...
The effect of implants of estradiol on initiation of ovarian cycles postpartum was studied in 201... more The effect of implants of estradiol on initiation of ovarian cycles postpartum was studied in 201 anestrous beef cows. Cows from four farms were used over a 2-yr period in a 2 x 3 factorial arrangement of treatments with estradiol implants and stage postpartum as main effects. Cows were assigned at random within date of calving within farm to receive an ear implant containing estradiol-17 beta (24 mg) for 21 d or to serve as controls. Stages postpartum at implantation were divided into less than or equal to 25, 26 to 39, and greater than or equal to 40 d, three stages that should reflect potential changes in hypothalmic-hypophysial sensitivity to estradiol. Blood samples for determination of progesterone were obtained and rectal examinations of the ovaries performed at implant insertion, 14 d after insertion, at implant removal (d 21), and 14 d after removal (d 35) to assess ovulatory response to treatment. Circulating concentrations of estradiol on d 14 of treatment averaged 3.2 +/...
Defining a common agenda to improve livestock contribution for poverty reduction in Latin America... more Defining a common agenda to improve livestock contribution for poverty reduction in Latin America and the Caribbean. ABSTRACT. The continuing prevalence of poverty and the existence of food insecurity are two of the major risk that threaten the development and stability of countries. Livestock has the possibility to contribute to the sustainable solution of both. In order to achieve this we must: a) Improve both the contribution of livestock to the national GDP and to individual family and producers incomes; b) Work to change the existing popular views around animal production and to reduce any possible impacts of animals to the environment and health; c) Improve the articulation and integration of value chains; d) Improve public policies in order to create an enabling environment for the activity and investment; and e) To bridge the distance between the agricultural innovation systems and the true needs of livestock and all the actors in the value chains. It is proposed that ALPA s...
Two experiments were designed to examine whether hormonal profiles were related to luteal life sp... more Two experiments were designed to examine whether hormonal profiles were related to luteal life span in pluriparous postpartum anestrous beef cows. Cows (Exp. 1, n = 34; Exp. 2, n = 23) received norgestomet (N) for 9 d or served as controls (C). Each cow received 1,000 IU human chorionic gonadotropin (hCG) 48 h after removal of N (d 0). Blood samples collected every 15 min for 8 h on d -5, 3 and 5 (Exp. 1) or on d -10 and -1 (Exp. 2) were assayed for luteinizing hormone (LH) and follicle stimulating hormone (FSH). Cortisol was determined in hourly samples collected on d -5 and in samples collected every 2 min during suckling on the same day (Exp. 1). Concentrations of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) were determined in samples collected at 15-min intervals for 2 h on d -5, 3, 5 and 10 (Exp. 1). Estradiol-17 beta was measured in samples collected on d -5 (Exp. 1) or on d -10 and -1 (Exp. 2). Life span of induced corpora lutea was longer (P less than .05) in N than C cows. Perce...
There is evidence that the dose of PGF(2)alpha generally used to synchronize estrus (25 mg) is hi... more There is evidence that the dose of PGF(2)alpha generally used to synchronize estrus (25 mg) is higher than required to induce luteolysis in cattle. To investigate this, 98 Holstein cows from three farms were assigned at random within farm to be treated with a single dose of 25 mg (n=33), 17.5 mg (n=33) or 10 mg (n=32) of PGF(2)alpha on Day 10+/-0.5 (mean +/- SEM) of the estrous cycle. Statistical analyses were conducted using analyses of variance and Chisquare test. Only 59.3% of the cows treated with 10 mg of PGF(2)alpha were detected in estrus compared with 72.7 and 78.7% of the cows treated with 17.5 and 25.0 mg doses, respectively (P>0.05). There were no differences (P>0.05) in pregnancy rates at the first service (40.0, 66.6 and 50.0% for 25, 17.5 and 10 mg, respectively). Concentrations of progesterone in blood were different (P<0.05) for cows treated with 10 mg compared with those of cows treated with 17.5 or 25 mg of PGF(2)alpha. The pattern of changes in progesterone concentrations between the last two groups was not different, and progesterone concentrations of less than 1 ng/ml of serum were observed within the first 36 h post PGF(2)alpha administration. In cows treated with 10-mg dose of PGF(2)alpha, concentrations of progesterone declined during the first 24 h, however, by the end of the experimental period, they were not different to pretreatment concentrations (treatment x time; P<0.05). It is suggested that reducing the dose of PGF(2)alpha from 25 to 17.5 mg do not affect estrus response or pregnancy rate in Holstein cows.
Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), proge... more Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone (P4) and estradiol-17 beta (E2) during an estrous cycle were compared between 15 lactating beef cows 5 to 7 years of age (young) and 15 cows greater than or equal to 12 years of age (old). Length of estrous cycle did not differ between young and old cows (P = .06). No differences due to age were found for LH. Patterns of concentrations of P4 during the first 15 days of the cycle, of FSH during days 6 through 12 and of E2 during the follicular phase differed with age (P less than .05). An earlier (P less than .025) midcycle elevation of FSH was associated with an earlier rise and greater concentration of E2 (P less than .05) during the follicular phase in old than in young cows. Differences in FSH and P4, although subtle, were consistent with an earlier or more advanced follicular development in old cows, leading to greater secretion of E2 from the preovulatory follicle.
... Intact Red Angus x Hereford heifers in the same herd reached puberty at 384 + 10 days (n6) in... more ... Intact Red Angus x Hereford heifers in the same herd reached puberty at 384 + 10 days (n6) in 1981, and at 410 + 7 (n=6) days in 1984. ... J Anim Sci 47:235240, 1978. 17. Nett TM, Crowder ME, Moss GE, Duello TM. GnRHreceptor interaction. ...
ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of... more ABSTRACT An experiment was conducted to test if suckling acutely suppressed circulating levels of LH during the postpartum period in beef cows. In addition, the influence of exogenous administration of low concentrations of estradiol on LH secretion during the postpartum period was evaluated. Twelve mature cows were randomly assigned before parturition to one of three treatments. Four intact cows were used as controls (INT). Eight cows were ovariectomized within the first 7 days following parturition. Four of these cows received a silastic 17β-estradiol implant subcutaneously at the time of ovariectomy (OVX-E); the remaining four cows received no further treatment (OVX). All cows were allowed to nurse one calf for 30 min daily between 1200 and 1230 hours for the duration of the experiment. Blood samples were collected at 12 min intervals for 6 hr before and 6 hr after suckling on days 9, 30, 44 and 58 postpartum. Mean interval (mean ± SE) to the first increase in peripheral progesterone concentrations indicative of the onset of ovarian luteal activity was detected in INT cows 37 ± 4.9 days postpartum. An acute effect of suckling on LH secretion did not occur in INT and OVX cows but mean LH concentrations were reduced in OVX-E cows following suckling on days 44 and 58. Mean LH concentrations remained low in INT cows; whereas, in OVX and OVX-E cows LH concentrations increased linearly (P<0.05) as the interval from time of ovariectomy increased. Cows in the OVX-E group had a higher mean concentration of LH than cows in the OVX group at 30, 44 and 58 days postpartum (P<0.05). Frequency of LH pulses did not differ between cows in the OVX and OVX-E groups at any period. Data from this experiment support the concept that suckling is acting in a chronic fashion to inhibit LH secretion during the postpartum period. In the absence of ovaries, chronic administration of exogenous estradiol in low concentrations has a positive effect on secretion of LH in the postpartum cow.
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