Ovar-DRB1 haplotypes *2001 and *0301 are associated with sheep growth and ewe lifetime prolificacy

The major histocompatibility complex (MHC) is an organized cluster of tightly linked vertebrate genes with immunological and non-immunological functions. While the important MHC gene DRB1 has been examined in regard to many sheep infectious disease traits, only one study, based on microsatellite markers, has previously examined DRB1 and sheep production traits. Furthermore, to our knowledge no studies have examined DRB1 relationship with lifetime ewe prolificacy traits. Therefore, we analyzed association between the presence of DRB1 SNP haplotypes with internationally recognized standard names and production traits including growth and lifetime prolificacy in 370 Rambouillet, Columbia, and Polypay sheep.

The DRB1 *2001 haplotype was associated with increased weaning and mature weights, as well as average daily gain (Šidák P<0.05; corrected for the number of haplotypes tested). Interestingly, the *2001 haplotype also showed a trend toward association with increased total number of lifetime lambs born (Šidák P=0.084) and number of lambs born alive (Šidák P=0.084). In contrast, the DRB1 *0301 haplotype was associated with decreased mature weight (Šidák P=0.01).

Since the *2001 haplotype was present in all three breeds, these results suggest there is at least one functional mutation in the region that influences growth and prolificacy traits that may be broadly present across several breeds. Furthermore, combined use of the similar *2001 and *0301 multi-marker haplotypes that nonetheless have opposing directions of production trait associations will enhance mutation discovery in this region. If undesirable alleles for underlying mutations can be identified, selective pressure against one or a small number of undesirable alleles may improve production with limited impact on MHC genetic diversity and infectious disease susceptibility.