Short-term selection for yearling weight in a small-experimental Iranian Afshari sheep flock

Ghafouri‐Kesbi, Farhad; Eskandarinasab, M P; Hassanabadi, Ahmad

doi:10.4141/cjas08059

Cited by 16 publications

(7 citation statements)

References 17 publications

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“…Somewhat lower estimates have also been reported by Ekiz (2005) in Turkish Merino lambs (0.08) for ADG from weaning to 6 months of age and by Miraei-Ashtiani et al (2007) in Sangsari lambs (0.05) for ADG from weaning to 6 months of age. The lower estimates of h 2 in the present study for post-weaning daily gain compared to other studies might be due to unfavorable environmental conditions which lambs experience during the post-weaning period (Ghafouri-Kesbi et al 2009). It is well known that trait heritabilities are not constant but can vary with environmental conditions (Ghafouri-Kesbi et al 2009).…”

Section: Discussionmentioning

confidence: 84%

“…The lower estimates of h 2 in the present study for post-weaning daily gain compared to other studies might be due to unfavorable environmental conditions which lambs experience during the post-weaning period (Ghafouri-Kesbi et al 2009). It is well known that trait heritabilities are not constant but can vary with environmental conditions (Ghafouri-Kesbi et al 2009). There are two alternate hypotheses that might explain this phenomenon.…”

Section: Discussionmentioning

confidence: 84%

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Genetic analysis of growth rate and Kleiber ratio in Zandi sheep

Ghafouri‐Kesbi

Abbasi

Afraz

et al. 2011

Trop Anim Health Prod

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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.

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Section: Discussionmentioning

confidence: 84%

Section: Discussionmentioning

confidence: 84%

Genetic analysis of growth rate and Kleiber ratio in Zandi sheep

Ghafouri‐Kesbi

Abbasi

Afraz

et al. 2011

Trop Anim Health Prod

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“…The aim of the experiment was to evaluate the response of Afshari sheep to selection for yearling live weight (selection criterion). The location of the experimental flock, husbandry practices and the results of the selection program were described by Ghafouri-Kesbi et al (2009).…”

Section: Datamentioning

confidence: 99%

“…To do such an evaluation, I used breeding values of the first 10 influential ancestors for the selection criteria (yearling weight) to evaluate change in their ranking when their genetic contributions were replaced with their breeding values. Breeding values of individual animals were obtained with the best linear unbiased prediction (BLUP) method (Ghafouri-Kesbi et al 2009). …”

Section: Measures Of Genetic Diversitymentioning

confidence: 99%

Using pedigree information to study genetic diversity and re-evaluating a selection program in an experimental flock of Afshari sheep

Ghafouri‐Kesbi

2012

Arch. Anim. Breed.

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The purpose of this paper was to evaluate the inbreeding consequences of a short-term selection experiment which was initiated in 1998 in an Afshari sheep flock. Moreover, the conducted selection experiment was re-evaluated through assessing change in ranking of the first 10 influential ancestors when their genetic contributions were replaced with their breeding values. A total of 1 714 animals were registered in the herdbook with a founder population comprised of 243 animals. The average coancestry (f) and inbreeding (F) in the reference population were 2.1 % and 1.2 %, respectively. Estimated value of the effective population size (N e ) was 50. The effective number of founders (f e ) was estimated to be 40 and the effective number of ancestors (f a ) was 34. Estimates of breeding values revealed that owing to phenotypic selection some ancestors with lower breeding values had greater contribution to the reference genome than those with greater breeding values and, for this reason, the population has been deprived from the maximum genetic improvement that could be achieved if selection was based on breeding values. The effective number of founder genomes (f g ) was computed to be 23 and the effective number of non-founder genomes (f ne ) was 55. The index of genetic diversity decreased by almost 2.2 % over the period studied. In general, decrease in genetic variability was low and N e was not very low for a small-closed population under selection, indicating even in populations which undergo selection, besides achieving genetic gain, the rate of inbreeding is controllable if matings carefully planned.

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“…The moderate pe 2 estimate for weaning weight indicates the importance of maternal permanent environment and maternal care during the period from birth to weaning, as lambs remained with their dams longer. Ghafouri-Kesbi et al (2009) reported that estimates of pe 2 are high at birth, when direct effects are the least important, but they decrease sharply after weaning and at the highest age this effect is negligible. However, Al-Shorepy et al (2002) found opposing results and related that although the permanent environmental effects had a higher influence on weaning weight than on birth weight, the genetic basis for these effects could not be interpreted.…”

Section: Genetic Parametersmentioning

confidence: 99%