International Journal of Poultry Science 8 (12): 1151-1155, 2009 ISSN 1682-8356 © Asian Network for Scientific Information, 2009 Effect of Genotype and Age on Egg Quality Traits in Naked Neck Chicken under Tropical Climate from India U. Rajkumar, R.P. Sharma, K.S. Rajaravindra, M. Niranjan, B.L.N. Reddy, T.K. Bhattacharya and R.N. Chatterjee Project Directorate on Poultry, Rajendranagar, Hyderabad 500 030, India Abstract: A comprehensive study was undertaken to evaluate the egg quality traits in three naked neck genotypes, NaNa (homozygous), Nana (heterozygous) and nana (normal) by utilizing 556 eggs collected at 28, 32, 36 and 40 weeks of age. The overall mean egg weight, shape index and Haugh unit values were 56.41 g, 75.79 and 75.98, respectively. The yolk index, yolk height and yolk colour varied significantly (p<0.01) in three genotypes. All other external and internal egg quality traits were not differed significantly among the genotypes; however Naked neck had better egg quality in almost all the traits. Age had significant (p<0.01) effect on all the traits studied in Naked neck chicken. Haugh unit score was better in 28 week age group. The egg, yolk, albumin and shell weights were positively correlated with the age. The average shell weight and thickness values were 5.07 g and 0.401 mm, respectively, which had no significant variation among the genotypes. The Na gene had marginal effect on all the egg quality traits studied. The better egg quality parameters in naked neck chicken are desirable which indicate the better keeping quality of the eggs and withstand the handling damages. Key words: Naked neck, egg quality, haugh unit, shape index and yolk index INTRODUCTION The Naked neck condition is characterized by complete absence or reduced feathers in the neck region of chicken controlled by an autosomal dominant gene (Davenport, 1914). The heterozygotes have a tuft of feathers on the ventral side of the neck (Scott and Crawford, 1977) whereas homozygotes have no plumage (Somes, 1988). The naked neck gene plays an important role in broiler production in tropical areas because of its association with heat tolerance (Merat, 1986; Lin et al., 2006) which is considered to be the most important inhibiting factor for poultry production in hot tropical climate (Horst, 1987). The Naked neck chicken has the ability to adapt, survive, perform and reproduce under harsh, hot and humid climatic conditions better than the normal feathered birds (Yakubu et al., 2008). Evaluation of external and internal quality of the egg is essential as consumers prefer better quality eggs. The Naked neck eggs have consumer preference because of its larger size, heavier weight and brown colouration. Stadelman (1977) described egg quality as the characteristics of an egg that affect its acceptability to the consumers. Many factors influence the egg quality i.e., breed/ strain/ variety, temperature, relative humidity, rearing practices and season (Sauter et al., 1954; Washburn, 1990). The success of poultry farming largely depends on the total number of good quality eggs produced especially in breeders. Though lot of work has been carried out on growth performance of naked neck chicken, the information on egg quality traits in naked neck birds are scanty. Islam and Nishibori (2009) reviewed the present status and prospects of naked neck chicken from Bangladesh and observed that the egg quality studies in naked neck chicken are limited. In the present study the effect of naked neck gene and age on different external and internal egg quality traits in three genotypes of Naked neck chicken were studied. MATERIALS AND METHODS The data on egg quality traits collected form three Naked neck genotypes maintained at Project Directorate on Poultry, Rajendranagar, Hyderabad, India, under selection for 6 week body weight for the last six generations were analyzed in the present study. The birds were identified phenotypically by the lack feathers (NaNa, homozygotes), tuft of feathers on the ventral side (Nana, heterozygotes) and full feathers (nana, normal) on the neck region. The birds were under restricted feeding schedule with a broiler breeder ration to maintain the desired body weight during growing and laying period. A total of 556 eggs were collected from the three genotypes at different ages i.e. 28, 32, 36 and 40 weeks and various external and internal egg quality traits were estimated. The external characters like egg weight, length and width were measured. Thereafter the eggs were broken and the internal traits like yolk weight, colour, height, albumin weight were recorded using standard procedure. Egg weight, Haugh unit, albumin height and yolk colour were measured using egg quality tester (EMT 5200, Japan). All the parameters were estimated using standard methods. 1151 Int. J. Poult. Sci., 8 (12): 1151-1155, 2009 The data were analyzed as per the standard methods (Snedecor and Cochran, 1994) using General Linear Model (GLM) procedure in SPSS 12.0 package. The effect of genotype and age on the different egg quality traits was assessed. The significance of differences of means among genotypes was tested with Duncan’s multiple range test. RESULTS AND DISCUSSION The findings are presented and discussed according to the genotype wise (Table 1) and age wise (Table 2). The analysis of variance revealed that the naked neck gene had significant effect (p<0.01) on yolk traits, while age had highly significant (p<0.01) on all the egg quality traits studied. Egg weight: The mean egg weight in NaNa, Nana and nana genotypes was 56.45, 56.72 and 56.11 g, respectively (Table 1). The Na gene had non significant effect on egg weight, though it was numerically better in Nana genotype. The gene had marginal positive effect on egg weight either in single or in double condition. The non significant effect of the gene may be because of the genetic similarity of the three genotypes which were produced from the same flock. The egg weight significantly (p<0.01) varied between the age groups except between 36 and 40 weeks which showed no significant variation (Table 2). The mean egg weight recorded was 56.41 g in Naked neck chicken. Islam et al. (2001) observed significant difference in egg weights between desi naked neck and full feathered chicken from Bangladesh, however it was significantly lower (40.5 g) compared to the present findings. Yakubu et al. (2008) reported lower egg weight (43.04 g) in Naked neck (NaNa) chicken from Nigeria under free range conditions. Egg weight variations in different genetic groups were reported by many authors (Washburn, 1990; Padhi et al., 1998; Chatterjee et al., 2007). Lower egg weights than the present study were observed in Naked neck (54.39±0.87), White Nicobari fowl (52.45±1.72), Brown, Black Nicobari (Chatterjee et al., 2007). Niranjan et al. (2008) observed lower egg weights in rural varieties (Vanaraja and Gramapriya) developed for backyard poultry. Mathivanan and Selvaraj (2003) reported higher egg weight (60.23 g) in IWH as compared to the naked neck chicken studied. The egg weights gradually increased as age increases showing the positive correlation between egg weights and age. The variation in egg weight may be attributable to the feed composition, feeding schedule and local environmental conditions. Shape index: Shape index is the ratio of the width to length of the egg. The average shape index was 75.79 in Naked neck chicken. The genotypes had no significant variation in the shape indices; naked neck gene had little positive effect (Table 1). The shape index was significantly (p<0.01) higher at 36 weeks of age indicating the more uniform egg shape, whereas significantly lower at 40 weeks of age. The shape index at 28 and 32 weeks did not show any significant variation. Yakubu et al. (2008) reported lower shape index of 74.65 for NaNa birds from Nigeria. Chatterjee et al. (2006) observed higher shape index, 80.76±1.32 for IWK and lower indices for IWI (73.77±3.08) and IWH (72.67±7.56) strains of White Leghorn. Lower shape index was observed for Naked neck (74.54) and higher for some other indigenous poultry breed of Andaman i.e., black, white and brown Nicobari fowl (Chatterjee et al., 2007) than the present study. The higher shape indices observed in the study may be because of the more uniform shape and size of the eggs. The egg length and egg width also showed the similar trend as that of shape index. Haugh unit: Haugh unit is the measure of albumin quality which determines the quality of the egg. The average Haugh unit values were 75.94 (NaNa), 76.36 (Nana) and 73.99 (nana) with a marginal positive effect of Na gene in either single or double condition. The genotype had no significant effect on the Haugh unit scores. Yakubu et al. (2008) observed comparable Haugh unit value (73.22) for NaNa genotype which differed significantly from normal feather counterparts in Nigerian local chicken. At 28 weeks of age Haugh unit scores were significantly (p<0.01) higher than other age groups (Table 2) which may attributable to the better albumin quality. Lower Haugh unit values of 73.16 in Naked neck was recorded by Padhi et al. (1998). Parmar et al. (2006) observed wide range of Haugh unit value for Kadaknath birds starting form 62.58-90.00 from India. Chatterjee et al. (2006) also reported lower Haugh unit values, 59.62-71.62 for the White Leghorn strains. The higher Haugh unit score in the Naked neck chicken indicated the superior quality of the albumin. Haugh unit values ranging from 100.25-106.29 were reported in crosses of naked neck, frizzle and normal chicken from Nigeria which are higher than the present values (Nwachukwu et al., 2006). Albumin Albumin weight: Albumin weight had no significant variation among the genotypes; however Naked neck genotypes had higher albumin weight (Table 1). The average albumin weight was 35.11 g in Naked neck chicken. Albumin weight was significantly (p<0.01) higher in age group 36 weeks compared to other age groups. Islam et al. (2001) reported lower albumin weight (20.7 g) in Naked neck birds than the present study. Lower albumin weights (23.46-26.67 g) than the present study were recorded by Chatterjee et al. (2007) in indigenous fowls of Andaman. The albumin weight 1152 Int. J. Poult. Sci., 8 (12): 1151-1155, 2009 Table 1: Egg quality traits in three genotypes of Naked neck chicken Parameter ------------------- Genotypes ------------------NaNa Nana nana n 152 281 123 Egg weight, g 56.45 56.72 56.11 Egg length, mm 57.92 58.12 59.41 Egg width, mm 44.03 43.86 44.21 Shape index 76.36 75.77 74.81 Haugh unit 75.94 76.36 73.99 Shell weight, g 5.12 5.02 5.07 Shell thickness, mm 0.40 0.41 0.39 Yolk colour 7.35b 7.63b 8.00a Yolk weight, g 17.09 17.05 17.78 Yolk height, mm 13.85b 14.24b 14.98a Yolk width, mm 38.83 38.91 39.39 Yolk index 35.82b 36.79ab 38.29a Albumin weight, g 34.24 34.65 33.26 Albumin height, mm 5.97 6.03 5.69 Albumin width, mm 75.88 74.74 76.07 Means with different superscripts within a row differ significantly (p<0.01) ------- Gene effect -----NaNa Nana SEM Prob 0.61 -2.51 -0.41 2.07 2.64 0.99 2.56 -8.13 -3.88 -7.54 -1.42 -6.45 2.94 5.29 -0.25 0.27 0.29 0.18 0.35 0.62 0.04 0.03 0.06 0.15 0.07 0.17 0.21 0.28 0.07 0.47 0.635 0.501 0.900 0.668 0.563 0.869 0.826 0.000 0.375 0.001 0.313 0.008 0.456 0.349 0.792 SEM Prob 0.27 0.29 0.29 0.35 0.62 0.03 0.003 0.06 0.15 0.07 0.17 0.21 0.28 0.07 0.47 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.015 0.000 0.000 0.000 1.09 -2.17 -0.79 1.28 3.20 -0.99 5.13 -4.63 -4.11 -4.94 -1.22 -3.92 4.18 6.35 -1.75 Table 2: Egg quality traits in Naked neck chicken at different ages Parameter ------------------------------------------- Age in weeks --------------------------------------28 32 36 40 Overall n 146 129 134 147 556 Egg weight, g 53.67c 56.29b 59.23a 59.96a 56.41 Egg length, mm 54.68b 55.83b 60.56a 61.71a 58.23 Egg width, mm 41.72c 42.35c 47.67a 44.10b 43.91 Shape index 76.58b 76.24b 78.96a 71.92c 75.79 Haugh unit 81.59a 75.12b 74.41b 72.40b 75.98 Shell weight, g 4.76b 4.54c 5.42a 5.52a 5.07 Shell thickness, mm 0.455a 0.388b 0.389b 0.372c 0.401 Yolk colour 8.39a 8.32a 8.10a 6.99b 7.93 Yolk weight, g 14.18d 16.07c 18.51b 19.72a 17.12 Yolk height, mm 13.61b 13.68b 14.93a 14.71a 14.23 Yolk width, mm 36.16c 37.97b 40.85a 40.83a 38.93 Yolk index 37.74ab 36.30c 36.79bc 36.07c 36.74 Albumin weight, g 34.73bc 35.68a 35.3ab 34.72c 35.11 Albumin height, mm 6.65a 5.77b 5.81b 5.60b 5.97 Albumin width, mm 67.12c 74.45b 79.24a 79.61a 74.99 Means with different superscripts within a row differ significantly (p<0.01) ranged from 28.6-31.1 g in rural varieties developed for backyard poultry (Niranjan et al., 2008) which was lesser compared to the Naked neck genotypes. The higher proportion of albumin may be because of the larger size of eggs recorded in the present study. Albumin height: Albumin height did not vary significantly among the three genotypes; however the naked neck genotypes had higher estimates compared to the normal birds. Na gene had positive effect on albumin height in both single and double condition. Albumin height was significantly (p<0.01) higher (6.65 mm) in 28 week age group compared to other age groups. Yakubu et al. (2008) observed lower albumin height (4.65 mm) in Naked neck chicken from Nigeria than the present estimates. Similar estimates for albumin height were reported in rural crosses by Niranjan et al. (2008). Yolk Yolk index: Yolk index values were significantly lesser in Naked neck genotypes (p<0.01), it was higher (38.29) in normal feathered birds (Table 1). The Na gene reduced the yolk index marginally. Higher yolk indices, 50.6 in NaNa birds (Yakubu et al., 2008); 41.0±0.01 to 45.0±0.01 in Nicobari varieties of Andaman (Padhi et al., 1998); 44-46 in rural varieties (Niranjan et al., 2008) were observed than the present findings. Chatterjee et al. (2007) reported lower yolk index in Naked neck chicken of Andamans. The yolk index significantly varied between the age groups with highest value of 37.74 in 28 week age group. Yolk weight: Yolk weight in the three genotypes NaNa, Nana and nana were 17.09, 17.05 and 17.78 g, respectively, which did not realize any significant variation. The lower yolk weights in Naked neck birds 1153 Int. J. Poult. Sci., 8 (12): 1151-1155, 2009 indicated that these eggs had lower fat percentage than the normal birds. Yolk weight at 36 and 40 weeks of age were significantly higher (p<0.01) compared to other two age groups (Table 2). Chatterjee et al. (2007) reported higher yolk weights in Naked neck, Barred desi and Frizzle fowl and lower yolk weights in brown and black Nicobari breeds of Andaman than the present findings. The yolk weight (16.95 g) in NaNa birds reported by Yakubu et al. (2008) was comparable to the present estimate, while Islam et al. (2001) observed lower (13.1 g) yolk weight in Naked neck birds. Yolk colour: Na gene significantly (p<0.01) reduced the yolk colouration. The yolk colour values were significantly higher in nana birds (Table 1). Yolk colour estimates were significantly (p<0.01) higher in 28, 32 and 36 weeks age groups. As age advances the yolk colour reduced gradually up to 40 weeks of age. Islam et al. (2001) reported lower estimates (4.5) for yolk colour in Naked neck chicken from Bangladesh. Shell Shell thickness: The average shell thickness was 0.401 mm in Naked neck chicken which had no significant variation among genotypes. The shell was significantly (p<0.01) thicker in 28 week age group compared to others. As age advanced the shell thickness gradually reduced (Table 2) with a significant lower shell thickness at 40 weeks of age. The higher shell thickness helps in preventing the damage during handling and also improves the keeping quality of the eggs. The mean shell thickness of 0.34 mm in Naked neck ( Islam et al., 2001); 0.30-0.34 in crosses involving Naked neck, Frizzle and normal birds (Nwachukwu et al., 2006); 0.31 in Kadaknath (Parmar et al., 2006); 0.33 in Nicobari, 0.31 in Naked neck and White Leghorn (Padhi et al., 1998) were lesser than the shell thickness observed in the present study. The shell thickness values reported by Niranjan et al. (2008) were comparable to the present findings. Yakubu et al. (2008) observed 0.38 mm thickness of the shell in Naked neck chicken from Nigeria which was marginally lower to the present values. The variations may be attributed to the feed composition utilized and the climatic conditions prevailing in the regions. Shell weight: Shell weight did not vary significantly among the three Naked neck genotypes. The average shell weight was 5.07 g accounting for 9% of the total egg weight. The shell weight was significantly (p<0.01) higher in 36 and 40 week age groups. The shell weight increased with egg weight showing the positive correlation between the traits. Non-significant differences were observed in Nicobari, Naked Neck and White Leghorn breeds for shell weight (Padhi et al., 1998). Chatterjee et al. (2007) also reported the non significant breed difference in shell weight for six indigenous chicken breeds from Andamans. Yakubu et al. (2008) and Islam et al. (2001) observed lower shell weight in Naked neck chicken from Nigeria and Bangladesh, respectively. Conclusion: Naked neck gene had a marginal effect on various egg quality traits studied. 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