GENETIC STUDIES ON THE PERFORMANCE OF NELLORE SHEEP
Loading...
Files
Date
2012-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sri Venkateswara Veterinary University, TIRUPATI – 517 502,A.P
Abstract
ABSTRACT :
Data on 1350 Nellore Jodipi sheep of 2, 4, 6 and 8-teeth age, reared under field conditions in 12 mandals of Chittoor district of Andhra Pradesh was utilized for the present study. Data recorded on body weights at different ages on the sheep maintained at the Network Project on Nellore Sheep Improvement, Livestock Research Station Palamaner, Chittoor district was also utilized for the present study.
Analysis of data under field conditions revealed that division and sex had significant (P≤0.01) effect on body weights and biometrical measurements at majority of ages studied and the non-genetic factors like Period, Season and Sex shown significant (P≤0.01) effect on body weights at all ages studied on farm data. The overall least squares means for body weight at 2, 4, 6 and 8-teeth age were 35.26 ± 0.23, 38.45 ± 0.13, 39.53 ± 0.32 and 40.06 ± 0.33 kg, respectively. While, the overall least-squares means for body weights at birth, 3, 6, 9 and 12 months of ages were 2.87 ± 0.01, 12.96 ± 0.08, 17.15 ± 0.13, 20.99 ± 019 and 25.38 ± 0.26 kg, respectively. The lambs born during off season shown superiority in body weights over main season lambs at all ages except at 9-months. The overall least-squares means for average daily gains during 0 to 3, 3 to 6, 6 to 9 and 9 to 12 months of ages were 112, 48, 42 and 49 gm, respectively.
Phenotypic correlations among body weights and biometrical measurements were also studied. The coefficients of correlations between body weight with the height at withers, chest girth, paunch girth hip width and body length were positive and high in magnitude in both males and females in majority of the age groups studied.
Step-down regression equations were fitted to predict the body weight based on biometrical measurements at different ages and the results revealed that the height at withers, chest girth, paunch girth, hip width and body length have contributed significantly to the expression of body weights at the majority of the ages studied. High Coefficient of determination (R2 values) were observed in males at 6 and 8-teeth age (88.00) males and in females at 2-teeth (50.00) age.
The data adjusted for non-genetic factors was utilized to study the genetic parameters. The heritability estimates were ranged from low to moderate. Body weights at six months of age was medium heritable (0.29 ± 0.08), while, 12 months of age was low heritable (0.062 ± 0.10). Heritability estimates for body weights at different ages tended to increase with increasing age from birth to 6-months body weight and then declined in the present study. The 6-months body weights can be used to select the animals for genetic improvement programmes.
The average daily gains during 3 to 6 months was medium heritable (0.340 ± 0.08). The heritability estimates for average daily gains at different ages tended to increase with increasing age from birth to 6-months average daily gains and then decreased. The average daily gains between 3 to 6 months age can be used as a selection criterion for the improvement of body weights.
The genetic correlation coefficients of weaning weight (3m) with 6, 9 and 12 months body weights and average daily gains during 0 to 3, 6 to 9 and 9 to 12 months of age were positive. The genetic correlations between 6-months body weight with later ages were strongly correlated.
The phenotypic correlation coefficients of 6 months body weight with 9 and 12 months body weights and average daily gains at all ages were positive and significant. The body weight at 6 months was highly correlated with 9 and 12 months body weights at genetic and phenotypic level also.
A greater portion of variation in body weights due to environmental factors was also observed, however, the genetic correlation suggested that selection can be practiced effectively at subsequent ages on the basis of body weights at 6 months of age to improve the body weights.
Description
Keywords
NELLORE SHEEP; GENETIC STUDIES