AN EVALUATION OF GENE INTERACTIONS AFFECTING CARCASS YIELD AND MARBLING IN BEEF CATTLE

Abstract

Genotype-specific management of beef cattle in feedlots has the potential to improve carcass uniformity. Gene variants affecting marbling include LEPc.73C>T, ADH1Cc.-64T>C, TG5, and GALR2c.-199T>G while those in CRHc.22C>G, POMCc.288C>T, MC4Rc.856C>G and IGF2c.-292C>T influence lean yield. The purpose of the current study was to assess combinations of marbling gene variants with those associated with lean yield and to investigate the effects of a gene variant in serotonin receptor 1B (HTR1B) on beef carcass traits. Gene variants were initially genotyped in 386 crossbred steers and evaluated for associations with carcass traits (hot carcass weight, average fat, grade fat and rib-eye area). The goal was to select a subset of variants to genotype in 2000 steers (1000 with hormone implants and 1000 without implants) with camera graded carcass data (Vision USDA yield grade, Vision grade marbling, rib-eye area and fat thickness). Seven gene variants were selected to proceed with (TG was discontinued) as they either had an association or were involved in gene interactions affecting a trait. In the implanted steers GALR2 affected rib-eye area (P=0.002) where it exhibited an additive effect (TT=83.74 cm2, TG= 84.32 cm2 and GG=86.90 cm2) however there was a dominant effect of the T allele for marbling (P=0.0001; TT/TG = 397.83 and GG=378.27) and fat (P=0.001; TT/TG=8.38 mm and GG=7.31). This same association with marbling (P<0.0001; TG/TT 463.52 mm and GG=430.90) and fat (P=0.006; TT/TG = 10.23 mm and GG=9.14 mm) was also observed in the non-implanted steers where again the T allele showed dominance. Gene-gene interactions affecting a trait were only observed in the non-implanted steers with the multivariate analysis: LEPc.73C>T and IGF2c.-292C>T with fat (P=0.05) and a trend with marbling (P=0.07); MC4Rc.856C>G and POMCc.288C>T with marbling (P=0.05); and GALR2c.-199T>G and POMCc.288C>T with rib-eye area (P=0.03). Associations between gene variants with traits were made simpler due to the fact that some genotypes could be collapsed, as least square means (LSM) were not significantly different, indicating a dominant effect of one allele. The ability to pool genotypes not only simplified the interactions, it resulted in a larger number of animals with combined genotypes. The gene SNP networks generated using EPISNP support the mode of action between gene variants. For example, the gene interaction that was a 3 by 2 was also determined to be Additive-Dominance. Significant associations were also identified between HTRIB c.205G>T SNP with carcass average fat (P=0.001), grade fat (P=0.007) and cutability (P=0.001) and a trend was observed with carcass REA (P=0.061). Although finding significance with several economically important carcass traits in crossbred beef breeds is novel, validating the effects of the HTRIB c.205G>T SNP in a larger cattle population would be beneficial.