Effect of Inbreeding on Genetic Parameters and Breeding Values for Production and Reproduction Traits in Holstein Cattle of Iran

Effects of inbreeding coefficient on estimates of genetic parameters, breeding values and genetic trends for production traits (milk, fat and protein yields), reproduction traits (age at the first calving, interval between first insemination to conception, calving interval, interval between calving to first insemination, and calving ease) as well as longevity of Holstein Cattle in Iran were studied. Inbreeding coefficients were computed using a complete pedigree, created from all available information of national Holstein dairy cattle and international sires back to 1883. For all the traits, the records of animals with a minimum pedigree completeness of 0.7 for five generations back were employed. The average completeness of pedigree for all the record holding animals was more than 0.90. Two univariate animal models (either with or without inbreeding) were considered to estimate the genetic parameters and breeding values. There were no substantial differences between the two models for variance components and genetic parameters. However, the effect of inbreeding on estimated breeding values and genetic gain was significant. Based on the estimated breeding values, the differences in male rankings were greater than those in female rankings for all the traits. Also, the rank correlations between two models ranged from 0.966 (milk yield) to 0.994 (fat yield) for males and 0.953 (calving ease) to 0.997 (age at the first calving) for females. These correlations, which were significantly different from unity, indicated that it is necessary to adjust the effect of inbreeding in genetic evaluation programs.