Inbreeding levels and their effects on phenotypic expression in Holstein cattle

The objective of the present study was to calculate the inbreeding levels in the Holstein population of Mexico and to evaluate their effect on the production of milk, fat, protein and final conformation points. The pedigree information was made up of 326,238 animals, to which inbreeding was calculated through the modified recursive algorithm (INBUPGF90). Inbreeding trends of animals born from 1990 to 2018 were obtained through a regression analysis, and the effect of inbreeding on productive characteristics was evaluated with an analysis of variances, for which phenotypic information from 68,779 animals was included. Six groups were formed according to the level of inbreeding (1= <1%, 2= >1 and <2%, 3= >2 and <3%, 4= >3 and <4%, 5= >4 and <5%, and 6> 5%). The results showed that, for each percentage point of increase in inbreeding, the production of milk, fat and protein decrease by 88, 3.16 and 2.57 kg (P<0.0001). At low levels of inbreeding (<5%), no effect on fat and protein production was detected. However, when inbreeding increased to more than 5 %, the loss in production was 12 kg of fat and 9 kg in protein. It was also observed that the animals with the lowest average conformation have low levels of inbreeding (<1%) and the highest levels did not show significant differences between them, which confirms that functional conformation is less sensitive to the effects of inbreeding than other characteristics of economic interest. It is recommended to promote selection programs based on optimal contributions to maximize genetic gains and control inbreeding levels.