Effect of Varying Dietary Vitamin A Supplementation Levels in Combination with ADH1C Genotype on Intramuscular Fat Deposition in Finishing Beef Steers

Previously, ADH1Cc.-64T>C was shown to have an association with intramuscular fat (IMF)  in the longissimus dorsi (LD) muscle when vitamin A was limited in finishing rations. The purpose of the current study was to determine the optimum vitamin A supplementation level, in combination with ADH1C genotype, to increase IMF of the LD muscle. Forty-five TT, 45 CT and 27 CC Black Angus-cross steers were backgrounded on a commercial ration containing 3360 IU vitamin A/kg DM. During finishing the steers were randomly assigned to one of three vitamin A treatments at 25, 50 and 75% of the NRC recommendation of 2200 IU/kg DM. Treatments were administered via an oral bolus. Carcass quality was evaluated and a sample from the LD muscle was collected for analysis of IMF. A treatment x genotype interaction (P=0.038) was observed for IMF; TT steers on the 75% treatment had higher IMF relative to CT and CC steers on the same treatment. Intramuscular fat was also higher for TT steers on the 75% treatment in comparison to TT steers on the 25% treatment. Eighty-four percent of the steers graded USDA AAA. Western blot analysis showed that TT steers had higher (P=0.0176) ADH1C levels in liver. Previously, TT steers had increased IMF when fed limited vitamin A.  In the current study the lack of variation between treatments and genotypes was likely due to the majority of the steers grading USDA AAA. However, the western blot data shows TT steers are expected to have higher IMF deposition.