Population structure and inbreeding effects on body weight traits of Guilan sheep in Iran

The objective of the present study was to describe the population structure and inbreeding to quantify their effects on body weights at different ages in Guilan sheep. The analysis was based on the pedigree information of 28,944 animals. Traits included were birth weight (BW, n = 14,549), 3-month weight (3MW, n = 13,109) and 6-month weight (6MW, n = 10,141). Data and pedigree information used in this study were collected during 1994-2011 by the Agriculture Organization of Guilan Province in Iran. All the animals were grouped into three classes according to the inbreeding coefficients obtained by their pedigree: the first class included non-inbred animals (F = 0%); and the second and third classes included inbred animals (0 < F ≤ 5% and F > 5%, respectively). The inbreeding depression was expressed as a partial linear regression coefficient estimated via a single trait animal model including fixed and random effects. The results of this study showed that the inbreeding coefficient of this population was very low (0.15%). The average relatedness was 0.000144572 and the generation interval was 2.385 years. The regression coefficients of BW, 3MW and 6MW on lamb inbreeding for a change of 1% in inbreeding were estimated to be −5.499 ± 0.66 (P < 0.0001), −28.406 ± 4.831 (P < 0.0001) and 20.078 ± 5.968 (P < 0.01), respectively. The utilization of a program for designed mating system, in the present flock, could be a suitable approach to keep the level of inbreeding under control.