Haplotypes affecting fertility in holstein cattle (review)

Abstract

The observed progressive increase of homozygosity in the cultural cattle breeds leads to increased negative impact of LoF-mutations (LoF - loss-of-function) in reducing cow fertility. Significant progress in the identification of LoF-mutations, which are associated with fertility, was achieved with the development of a new approach called «homozygosity mapping» (C. Charlier et al., 2008). This approach allows identifying the chromosomal regions characterized by loss of homozygosity, which are the candidate regions for location of fertility haplotypes associated with embryonic and early post-embryonic mortality. In the past few years, the fertility haplotypes were identified in almost all the major breeds of dairy cattle: Holstein (P.M. Van Raden et al., 2011; S. Fritz et al., 2013; T.A. Cooper et al., 2013), Jersey (P.M. Van Raden et al., 2011; T.S. Sonstegard et al., 2013), Brown Swiss (P.M. Van Raden et al., 2011; T.A. Cooper et al., 2013; M. McClure et al., 2013), Montbeliarde (S. Fritz et al., 2013), Ayrshire (T.A. Cooper et al., 2013), Fleckvieh (H. Pausch et al., 2015), Nordic Red cattle (N.K. Kadri et al., 2014). In presented review, it is characterized the haplotypes affecting fertility, which are segregated in Holsteins - the main dairy cattle breed worldwide (bred in 161 countries). In Russia, the ratio of Holstein and holsteinized Black-Pied cattle accounted for more than 65 % of common dairy cattle population. Currently, in the Holstein breed is registered ten fertility haplotypes (HCD, HH0, HH1, HH2, HH3, HH4, HH5, HHB, HHC, HHD), which affect the pregnancy losses and/or associated with embryonic and early post-embryonic mortality at different stages (J.B. Cole et al., 2016). Possible causes for segregation of the fertility haplotypes in cattle populations are discussed. These are intensive use of carrier bulls for artificial insemination, a considerable period from occurrence to the identification of causative mutations (18-59 years), the possible association of carrier status with productive traits. The chromosomal location of the fertility haplotypes is characterized, the haplotype frequencies in North-American Holstein population are presented and the effects of bull carrier status on cow pregnancy rate are shown. It is described the stages of pregnancy and/or the age of calves on which there is the embryonic mortality of affected fetus and/or the death of affected calves. It is characterized the genes and the causative LoFmutations, which are associated with fertility haplotypes. It is shown that more than 5 % of sires used in Russia have had the fathers, which are the carriers of fertility haplotypes. Thus, it is necessary to screen the Russian population of Holstein and holsteinized cattle to detect the carrier status of animals. The role of DNA-diagnostics in the control and elimination of fertility haplotypes and associated genetic defects in the Russian population of breeding cattle is discussed. Survey for these latent genetic defects among domestic Holstein and holsteinized Black Pied cattle showed that they occur at a relatively high rate, reaching about 10 % for cows and about 4 % for bulls. Among the bulls more than 5 % were hidden CVM carriers, and about 3 % were latent BLAD carriers. Currently, due to genetic monitoring, these mutant alleles are not being recorded in sires of the population.