Study of pedigree structure and effects of inbreeding depression on growth traits in Lorestan native sheep

Inroduction: Inbreeding is defined as the probability that two alleles at any locus are identical by descent and occur when related individuals are mated to each other. The initial consequence of inbreeding is inbreeding depression reducing the performance of growth, production, health, fertility, and survival traits. This concern has become more serious in animal breeding nowadays, in which selection responses are maximized using animal model best linear unbiased predictors (BLUP) of breeding value. The use of these breeding values alone may result in more closely related selection candidates preferred for selection, with increased levels of inbreeding since they share most of their familial information. The unavoidable mating of related animals in closed populations leads to accumulation of inbreeding and decreased genetic diversity. Inbreeding has deleterious effect on additive genetic variance as well as on phenotypic values. Heterozygosity and allelic diversities can be lost from small, closed, selected populations at a rapid rate. The rates of inbreeding must be limited to maintain diversity at an acceptable level so that genetic variation will ensure that future animals can respond to changes in environment. Inbreeding depression has been found in a large proportion of species examined. Lori sheep breed is mainly raised in Lorestan Province in Iran. This study was conducted to identify pedigrees and inbreeding depression on growth traits in Lori sheep population from 2001 to 2010. The rate of inbreeding needs to be limited to maintain diversity at an acceptable level so that genetic variation will ensure that future animals can respond to changes in the environment and to selection. Without genetic variation, animals cannot adapt to these changes. For this study pedigree information and body weight at different ages (birth weight, weaning weight, 6-month weight, and 9-month weight) of 6440 lambs from 273 rams and 1955 ewes during the years 2001 to 2010 from Lorestan Agricultural and Natural Resources Research Center were used. The pedigree corrections were done by the Excel program and the estimation of inbreeding coefficients was done by pedigree software. To study the pedigree, Pedigree, program, or estimate inbreeding coefficient, CFC program, and for calculate the amount of inbreeding citizenship traits, wombat software were used. In total population the number of inbred animals were 2126 (33%) of the herd. The average total population inbreeding coefficient and average inbreeding coefficient inbred of population were 0.69% and 2.24%, respectively. Annual changes in inbreeding coefficient was 0.21, which was statistically significant (p