Feedlot Performance and Immunology of Beef Steers Fed a Low Vitamin A Diet and Selected for ADH1C Genotype

Marker-Assisted Management (MAM) is gaining interest among feedlots as they are continually striving to minimize costs while maximizing returns. By employing MAM and precision feeding animals based on genotype, consistency within a pen can be achieved. In two previous nutrigenomic studies on vitamin A (VA) and ADH1Cc.-64T>C genotype, TT hormone-free black Angus cross steers fed reduced VA had increased intramuscular fat. The current study investigated the effects of two levels of dietary VA (NRC (2,200IU/kg/DM) and 50% of NRC) with ADH1Cc.-64T>C genotypes (TT or CT), and implant status (implanted or non-implanted) in 2000 feedlot steers not selected for colour. This 2x2x2 factorial design resulted in several significant 3-way interactions (P<0.05), however upon further investigation, it appears these interactions were based on implant status alone. No two-way interaction between genotype and VA, and no main effects of these variables were observed. Further investigation is required to explain fully why we did not observe main or interaction effects with marbling. Another VA-ADH1C nutrigenomics question is regarding the effect of the reduced level of VA on immune function. Black beef steers (TT, CT, or CC on 25% or 75% of NRC recommended VA; n=18) from a previous VA-ADH1C feeding trial were sampled to determine differential blood cell counts and PBMC proliferation levels. No significant difference (P<0.05) in any immune function parameter studied was observed. This suggests that among the parameters tested, a reduction of as much as 75% of the NRC recommendation for VA should not negatively impact immune function in beef cattle.