Inbreeding and its effect on milk production traits of Iranian Holstein cattle

In order to investigate the rates of inbreeding trend and also the effect of inbreeding on milk, fat and protein yields, the pedigree data of 2,394,517 Iranian Holstein cattle from 1986 to 2019 which collected was used. CFC software was utilized to calculate the inbreeding coefficients, and WOMBAT program was applied to estimate the inbreeding depression by determining regression coefficient of production traits on inbreeding coefficient. The average of inbreeding coefficients in the whole population and inbred animals were estimated as 0.777 and 1.681 percent, respectively. In general, the rate of inbreeding trend was positive and for recent years it was 0.17 percent per year. However, this rate was estimated as -0.29 percent per year for inbred animals, the number of inbred animals was increasing. Examination of the effect of inbreeding on production traits showed that per 1 percent increase in inbreeding coefficient resulted in 11.87, 0.39 and 0.29 kg decrease in milk, fat and protein yields, respectively. The use of domestic sperms and cows has limited the population and increased relative mating. However, close relative mating has been controlled. The existence of negative effect of inbreeding on production traits and on the other hand, increasing the number of inbred animals indicates that breeding and mating strategies of animals need to be continuously reviewed, and if it is necessary close relative mating can be limited using imported sperms.