International Eurasian Conference on Biotechnology and Biochemistry (BioTechBioChem 2020), Ankara, Turkey, 16 - 18 December 2020, vol.1, pp.115
Milk yield and reproductive performance are two major traits in dairy cattle breeding. In the great majority of countries, dairy cattle are under increased stress in their management for high milk production. Accordingly, genetic evaluation in dairy cattle focuses on the determination of the genotypic background influencing milk yield and composition. It is important to note that a negative relationship between milk production traits and cow’s fertility has been continually declared in dairy cattle. Selection for improved milk yield performance has caused an eventual decline of cow fertility, especially for Holsteins. Recently, decreased profitability and sustainability as a consequence of decreased reproductive performance have gradually led to an increased interest in non-production traits, including reproductive efficiency, longevity, and health. Dairy cow fertility is a very complex trait and it consists of several sub-traits including age at first calving, first insemination to pregnancy interval, calving interval, days before the first insemination, number of inseminations required for conception, gestation length, and calving ease. Moreover, an unfavorable genetic association of reproductive disorders with milk production, insufficient records, management factors, and the impact of environmental conditions make the situation more complex and complicate the analysis of the traits. On the other hand, many reproduction traits have low heritabilities, usually less than 5%, and they are difficult to ascertain concerning parameter estimation and genetic evaluation. Contemporary genomic studies have enabled the development of effective and highly accurate selection methods but it is important to include all important aspects of fertility to achieve a good and expected selection response. Taken altogether, the present assessment aimed to perform a comprehensive comparison between cow milk production and fertility based on genomic approaches. There has been a growing interest in broadening selection indices to include functional traits, such as reproduction and health. The information represented here can provide important points for an adequate genotypic evaluation of dairy cattle reproduction performance.