Ruminant Nutrition: Dairy - Lactation, Health & Gut Physiology

Recent research has shown a negative correlation between marbling and serum retinol concentration in Japanese Black cattle. Three hundred sixty single-source black, yearling steers (average initial BW = 316 ± 9.1 kg) fed a 91 % concentrate (steam-flaked corn base) diet were used to evaluate the effects of supplemental vitamin A concentration on performance, DMI, and carcass traits. Steers were blocked into eight weight replicates and assigned randomly to pens (n = 9/pen) and to diets containing 0, 1,103, 2,205 4,410, or 8,820 IU of supplemental vitamin A/kg DM. Daily DMI, ADG, and feed:gain ratio were determined for each 28-d period and for the overall 142-d trial. Final BW (586, 580, 590, 584, and 584 kg for 0, 1,103, 2,205 4,410, and 8,820 IU vitamin A/kg DM, respectively) did not differ (P > 0.10) among treatments. Feed efficiency, ADG, and daily DMI also did not differ (P > 0.10) among treatments within each 28-d period or for the overall trial. From d57 to harvest, average DMI (10.33, 10.28, 10.57, 9.75, and 10.22 kg/steer daily for 0, 1,103, 2,205, 4,410, and 8,820 IU vitamin A/kg DM, respectively) was lower (P < 0.02) for steers receiving 4,410 IU vitamin A/kg DM than for steers in other treatments, and DMI was greater (P = 0.06) for the 2,205 IU vitamin A/kg DM treatment than for the 8,810 IU/kg DM treatment. Marbling score, hot carcass weight, longissimus muscle area, and 12th rib fat thickness did not differ (P > 0.10) among treatments. Similarly, the number of carcasses grading ≥ Choice (62.6, 52.8, 64.0, 58.4, and 58.4 % for 0, 1,103, 2,205, 4,410, and 8,820 IU vitamin A/kg DM, respectively), Select, or ≤ Standard did not differ (P > 0.10) among treatments. Results of this trial suggest that vitamin A supplementation up to twice the NRC-suggested concentration has little effect on performance or marbling in typical yearling feedlot steers.