Investigation of genetic variability and inbreeding characteristics in a population of Zandi sheep

Abstract

Ghafouri-Kesbi, F., Eskandarinasab, M. and Hassanabadi, A. 2008. Investigation of genetic variability and inbreeding characteristics in a population of Zandi sheep. Can. J. Anim. Sci. 88: 409Á417. The aim of the present study was to evaluate the genetic parameters and genetic trends for birth and weaning weights, and to quantify the inbreeding characteristics for a population of Zandi sheep. Genetic parameters from both single-and two-trait analyses were estimated using restricted maximum likelihood (REML) with animal models. Genetic trends were estimated by averaging estimated breeding values on year of birth. Full pedigree was analyzed for estimation of inbreeding characteristics. The results obtained confirmed relatively low additive genetic variation in the population, especially for weaning weight. Estimates of direct and maternal heritability were 0.12 and 0.20 for birth weight and 0.08 and 0.02 for weaning weight, respectively. Estimates of breeding values averaged by year of birth for birth weight and weaning weight increased over time. However, there was little genetic progress for birth weight (0.002 kg yr(1 ), whereas the tendency for weaning weight was 0.020 kg yr Á1 . Inbred animals consisted of 25% of the population. The effective population size (Ne) was 66 individuals. The inbreeding rate per generation (DF) was 0.76%. The average value of inbreeding (F) in the Zandi population was 1.05% and the average relatedness (AR) coefficient reached 1.64% in the whole pedigree. A range of 2.84 to 4.01 yr was obtained for the average generation interval in different pathways. Selection of rams with the lowest AR was recommended for better management of inbreeding and avoidance of relative mating.Key words: Sheep, genetic trends, heritability, inbreeding, average relatedness Ghafouri-Kesbi, F., Eskandarinasab, M. et Hassanabadi, A. 2008. É tude de la variabilite´ge´ne´tique et de la consanguinited 'une population de moutons Zandi. Can. J. Anim. Sci. 88: 409Á417. L'e´tude devait e´valuer les parame`tres ge´ne´tiques du poids a`l'agnelage et au sevrage d'une population de moutons Zandi, et en quantifier la consanguinite´. Les parame`tres ge´ne´tiques des analyses d'un et de deux caracte`res ont e´te´estime´s par la me´thode du maximum de vraisemblance restreint (REML) sur des mode`les animaux. Les tendances ge´ne´tiques ont e´te´e´value´es par re´gression des valeurs reproductives, estime´es selon l'anne´e de naissance. Les sujets enregistre´s ont e´te´analyse´s afin d'en e´valuer la consanguinite´. Les re´sultats confirment une variation ge´ne´tique par addition relativement faible, surtout pour le poids au sevrage. L'he´re´dite´directe et l'he´re´dite´maternelle s'e´tablissent respectivement a`0,12 et 0,20 pour le poids a`la naissance et a`0,08 et 0,02 pour celui au sevrage. La valeur reproductive moyenne pour le poids a`l'agnelage et au sevrage estime´e selon l'anne´e de naissance augmente avec le temps. Toutefois, le poids a`la naissance progresse peu sur le plan ge´ne´tique (0,002 kg par anne´e), tandis q...

Analysis of genetic diversity in a close population of Zandi sheep using genealogical information

“…The location of the experimental flock as well as their natural habitat, description, and husbandry practices were described by Ghafouri-Kesbi et al (2008).…”

Assessment of mating management effect on genealogical parameters highlighting the genetic variability in a not closed fat-tailed Barbarine sheep pedigree

“…Thus, one can conclude that the genetic variability within an open flock might be monitored more appropriately by using the average relatedness; even if the population is not concerned by a conservation program as argued by Oliehoek et al (2006). A similar conclusion was carried out by Goyache et al (2003) and Ghafouri-Kesbi et al (2008).…”

“…However, under the pedigree depth, more lambs are born inbred. But, with an experimental herd, where also some selection schemes were tested, the inbreeding is not avoidable (Ghafouri-Kesbi et al 2008). Nevertheless, in spite of this broad proportion, it is possible to maintain or even minimise inbreeding rate by managing the matings at each generation following specific strategy like this proposed by Sánchez et al (2003).…”

What can livestock breeders learn from conservation genetics and vice versa?

“…Populations of domestic animals with a small Ne can also exhibit reduced genetic variation compared to ancestral ones ( Ghafouri-Kesbi et al, 2008 ; Kim et al, 2013 ; Freedman et al, 2014 ; Quaresma et al, 2014 ). For example Freedman et al (2014) found that the domestication process of dogs resulted in reduced genomic variation consistent with at least a 16-fold reduction in population size.…”