Genetic analysis of growth rate and Kleiber ratio in Zandi sheep

Abstract

Genetic parameters for average daily gain from birth to weaning (ADGa), birth to 6 months (ADGb), weaning to 6 months (ADGc), weaning to yearling age (ADGd), and corresponding Kleiber ratios (KRa, KRb, KRc, and KRd) were estimated by using records of 3,533 Zandi lambs, descendent of 163 sires and 1265 dams, born between 1991 and 2005 at the Zandi Sheep Breeding Station at Khojir National Park, Tehran, Iran. A derivative-free algorithm combined with a series of six single-trait linear animal models was used to estimate phenotypic variance and its direct, maternal, and residual components. In addition, bivariate analyses were done to estimate (co)variance components between traits. Estimates of direct heritability (h(2)) were 0.11, 0.15, 0.09, 0.10, 0.10, 0.10, 0.06, and 0.07 for ADGa, ADGb, ADGc, ADGd, KRa, KRb, KRc, and KRd, respectively, thereby indicating the presence of low additive genetic variation for growth rate and Kleiber ratio in this population of Zandi sheep. Maternal genetic component was found to be significant on ADGa and KRa and contributed 3% and 5%, respectively, in total phenotypic variance of ADGa and KRa. A widespread range of genetic correlations among traits studied was observed. Except for negative genetic correlations between ADGa and KRc, ADGa and KRd, and between KRa and KRc, in other cases, genetic correlations were positive and moderate to very high. Phenotypic correlations ranged from -0.49 (ADGa/KRd) to 0.94 (ADGc/KRc). These results indicate that selecting for improved growth rate or Kleiber ratio in Zandi sheep would generate a relatively slow genetic progress.

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.…”

“…Likewise, PRINCE et al (2010), using similar animal model, published report of 0.00±0.00 in Avikalin sheep and GHAFOURI- KESBI et al (2011) obtained h 2 m equal to 0.03±0.01. The low estimate indicates diffi culty in improving maternal ability for average daily weight gain from birth to weaning and reinforces the fact that the early growth is also determined by maternal effects.…”

“…Table 1 lists the comparison between the three models by the likelihood ratio test in order to estimate the heritability for body weight and average daily gain. From table 1, it is observed the importance of the maternal effects to estimate genetic parameters for growth traits, since the non-inclusion of these effects overestimated the heritability coeffi cients, as highlighted in several studies with different sheep breeds (MANIATIS & POLLOTT, 2002;EKIZ et al, 2004;MANDAL et al, 2006a;GHAFOURI-KESBI et al, 2011).…”

Genetic parameters for growth rate and Kleiber ratios of Nellore sheep

“…Likewise, estimates of phenotypic correlations among growth rate and Kleiber ratios traits at different stages of growth were in the range of -0.24 (ADGa-Kb) to 0.89 (ADGb-Kb). These results were comparable with the findings of Ghafouri-Kesbi et al, (2011), Savar-Sofla et al, (2011, Mokhtari et al, (2012), Prakash et al, (2012) andKesbi, (2013).…”

<b>Genetic components of birth weight of texel sheep reared in extensive system

“…There are two alternative hypotheses that may explain this phenomenon. First, the genetic variation of the quantitative traits may change as a direct response to the environmental conditions in which they are expressed, and second, the harsh rearing environment inflates the error variance and results in lower heritability estimates (Ghafouri-Kesbi, Abbasi, Afraz, Babaei, Baneh, & Abdollahi Arpanahi, 2011). Therefore, the authors refer to the influence of maternal effects, when the phenotype of a mother or the environment it experiences, has a phenotypic effect on the offspring.…”