Estimates of (co)variance components and genetic parameters for growth traits of Avikalin sheep

Abstract

(Co)variance components and genetic parameters for various growth traits of Avikalin sheep maintained at Central Sheep and Wool Research Institute, Avikanagar, Rajasthan, India, were estimated by Restricted Maximum Likelihood, fitting six animal models with various combinations of direct and maternal effects. Records of 3,840 animals descended from 257 sires and 1,194 dams were taken for this study over a period of 32 years (1977-2008). Direct heritability estimates (from best model as per likelihood ratio test) for weight at birth, weaning, 6 and 12 months of age, and average daily gain from birth to weaning, weaning to 6 months, and 6 to 12 months were 0.28 +/- 0.03, 0.20 +/- 0.03, 0.28 +/- 0.07, 0.15 +/- 0.04, 0.21 +/- 0.03, 0.16 and 0.03 +/- 0.03, respectively. Maternal heritability for traits declined as animal grows older and it was not at all evident at adult age and for post-weaning daily gain. Maternal permanent environmental effect (c(2)) declined significantly with advancement of age of animal. A small effect of c(2) on post-weaning weights was probably a carryover effect of pre-weaning maternal influence. A significant large negative genetic correlation was observed between direct and maternal genetic effects for all the traits, indicating antagonistic pleiotropy, which needs special care while formulating breeding plans. A fair rate of genetic progress seems possible in the flock by selection for all traits, but direct and maternal genetic correlation needs to be taken in to consideration.

Model comparisons and genetic parameter estimates of growth and the Kleiber ratio in Shal sheep

“…Such appropriate selective procedure requires accurate (co)variance components and genetic parameter estimates. Genetic parameters for growth traits of different sheep breeds have been reported (Prince et al 2010, Di et al 2011, Abegaz et al 2010. The results of these studies have shown that the inclusion of maternal effects on the models considered for genetic analysis of growth traits, especially for pre-weaning traits, is of crucial importance.…”

Estimates of (co)variance components and genetic parameters for growth traits in Suffolk lambs

“…Studies with different sheep breeds have shown that both direct and maternal genetic effects act on lambs' growth performance (MARÍA et al, 1993;SNYMAN et al, 1995;MANDAL et al, 2006a, b;PRINCE et al, 2010), thus, to achieve greater genetic progress in selection programs and increased accuracy in estimates, both components need to be considered in genetic models (MEYER, 1992).…”

Estimativas de parâmetros genéticos para características de crescimento de cordeiros mestiços Suffolk

“…Nota-se ainda que os coeficientes de herdabilidade materna estimados para PN e PD apresentaram magnitudes baixas, a partir do modelo mais apropriado. Para PN, o valor encontrado foi semelhante ao reportado por Matika et al 16 (0,12±0,03), e superior aos obtidos por Kushwaha 2 (0,09±0,04) e Prince et al 3 (0,08±0,03). Em artigo de revisão, Safari et al 17 relataram que as estimativas de herdabilidade materna para peso ao nascer para raças de dupla aptidão (carne e lã) variam entre 0,18 e 0,24.…”

“…Em artigo de revisão, Safari et al 17 relataram que as estimativas de herdabilidade materna para peso ao nascer para raças de dupla aptidão (carne e lã) variam entre 0,18 e 0,24. Já para PD, os coeficientes geralmente apresentam menores magnitudes conforme encontrado em outros trabalhos realizados com diferentes raças de ovinos, como 0,10 17 , 0,08 7 e 0,01±0,01 3 , observado também no presente estudo. A diminuição da importância dos efeitos maternos sobre os pesos dos cordeiros com o aumento da idade do animal é esperada 18,19 , apresentando importância em mamíferos, sobretudo em animais jovens 20 .…”

“…A escolha do modelo adequado na obtenção de parâmetros genéticos pode levar em consideração os efeitos aditivo direto, genético materno e de ambiente permanente materno. Estudos com diferentes raças de ovinos mostram que ambos os efeitos genéticos direto e materno atuam em períodos pré e pós-desmama de cordeiros [1][2][3] , indicando que, quando não incluídos nos modelos de análise, as estimativas tornam-se inflacionadas.…”