Different models for evaluation of growth traits and Kleiber ratio in an experimental flock of Iranian fat‐tailed Afshari sheep

Abstract

Records for Afshari sheep were retrieved from data collected between 2000 and 2005 at the Zanjan University experimental flock, at Zanjan, Iran. (Co)variance components and corresponding genetic parameters for birth weight (BW), weaning weight (WW), 6-month weight (W6), average daily gain from birth to weaning (ADGa), from birth to 6 months (ADGb), from weaning to 6 months (ADGc), Kleiber ratio at weaning (WWKR) and Kleiber ratio at 6 months of age (W6KR) were estimated using univariate and bivariate analyses by the DFREML procedure. The Kleiber ratio, defined as growth rate/metabolic weight, has been suggested to be a useful indicator of growth efficiency and an indirect selection criterion for feed conversion. Estimates of direct heritability (h(2)) were 0.23, 0.27, 0.11, 0.22, 0.07, 0.01, 0.13 and 0.06 for BW, WW, W6, ADGa, ADGb, ADGc, WWKR and W6KR, respectively. Maternal genetic effects represented a relatively large proportion of the total phenotypic variance for BW (m(2) = 0.22), whereas maternal permanent environmental effects were significant for W6 (c(2) = 0.15), ADGb (c(2) = 0.16), ADGc (c(2) = 0.14) and W6KR (c(2) = 0.16). Results of bivariate analyses indicated the variable genetic correlations between traits. The largest positive genetic relationships were between adjacent measurements. The moderate estimates of h(2) for early growth traits indicate that in Afshari sheep faster genetic improvement through selection is possible for these traits. In order to increase the efficiency of feed conversion, use of Kleiber ratio in selection programmes was recommended.

Genetic parameters for direct and maternal effects on growth traits of sheep

“…Among traits studied, BW had the minimum CV. Miraei-Ashtiani et al (2007) in Sangsari sheep and Eskandarinasab et al (2010) in Afshari sheep reported similar findings. The reason of less CV for BW may be due to less variation and effect of outside environment on this trait, as ewes were kept inside and manually fed in the late months of pregnancy period in the winter (MiraeiAshtiani et al 2007).…”

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

“…In relation to ADG1, heritability values reported in the literature range from 0.11 to 0.22 (ABEGAZ et al, 2005;ESKANDARINASAB et al, 2010;GHAFOURI-KESBI et al, 2011), higher than those found in this paper. For ADG2, the estimate was in range with fi ndings of ESKANDARINASAB et al (2010) were similar to the results presented.…”

Genetic parameters for growth rate and Kleiber ratios of Nellore sheep

“…The heritability estimates for average daily gains during (birth-3 months), (3-6 months) and (6-12 months) periods were 0.20±0.06, 0.24±0.07 and 0.17±0.06 and the corresponding Kleiber ratios were 0.25±0.07, 0.23±0.06 and 0.17±0.06, respectively. The heritability estimates of pre weaning growth rates were within the range of literature (Eskandarinasab et al, 2011;Mohammadi et al, 2011;Prakash et al, 2012;Savar-Sofla et al, 2011;Mokhtari et al, 2012 andKesbi, 2013). Literature suggested that heritability estimates for post weaning growth rates of various sheep breeds had wider range where the estimates ranged from 0.02 in Moghani sheep (Savar-Sofla et al, 2011) to 0.70 in Menz sheep (Gizaw and Jushi 2004).…”