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چکیده
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The objective of this study was to evaluate inbreeding and inbreeding depression in Baluchi sheep. Dataand pedigree information were retrieved from the Baluchi sheep Breeding Station, Khorasan Razavi, Iran.Traits included were birth weight (BW), weaning weight (WW), 6-month weight (W6), 9-month weight(W9), yearling weight (W12), average daily gain from birth to weaning (ADGa), average daily gain fromweaning to 6 months of age (ADGb) and average daily gain from weaning to 12 months of age (ADGc).Animals were grouped in three classes: first class included non-inbred animals (F = 0) and second andthird classes included inbred animals (0 < F ≤ 5% and F > 5%, respectively). Inbreeding depression wasstudied for all traits by fitting individual increase in inbreeding coefficient (Fi) of the lambs as linearcovariates under univariate animal models. The mean inbreeding in the whole population was 1.60%. Itincreased with some fluctuations from 1981 to 2005 and decreased thereafter. The average equivalentcomplete generation, as a measure of pedigree completeness, in the studied population was 2.49 and thevalue of effective population size (Ne) estimated from the Fiwas 166. Of 10863 pedigreed lambs, 5931,3943 and 989 animals belonged to first, second and third inbreeding class, respectively, with significantdifferences in their body weights and average daily gains. In some cases, growth traits of male and femalelambs as well as single and twin lambs grouped in three inbreeding classes differed significantly. Amongtraits studied, W6, W9, W12, ADGb and ADGc were significantly affected by inbreeding (P < 0.01) in sucha way that one percent increase in Fiof the lambs significantly reduced W6, W9, W12, ADGb and ADGcby 18, 10, 131, 1.810 and 1.345 g, respectively. Selection of rams with the lowest relationship with ewesin the flock was recommended to decrease the rate of inbreeding in the population.
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