Effects of Vitamin A and Restricted Intake on Performance, Carcass Characteristics, and Serum Retinol Status in Angus × Simmental Feedlot Cattle

Three feedlot experiments examined the effects of vitamin A (VA) on marbling and serum retinol (ROL) in Angus × Simmental cattle. Diets contained 2300 [low VA (LVA)] or 7250 IU VA/ kg [high VA (HVA)]. In Exp. 1, 48 early weaned (51.0 ± 2.2 d) heifers (309.3 ± 7.0 kg; 12 pens) were fed ad libitum or were limit-fed 70 or 85% of ad libitum intake for 183 d then were fed for ad libitum intake for 149.3 ± 4.1 d. Vitamin A treatments were fed for 163.3 ± 4.1 d, and heifers were harvested at compositional endpoints. Serum was collected three times during the experiment. Limitfed heifers had improved (P<0.05) feed efficiency, but reduced marbling and yield grade. Intermediate and final ROL were greater in HVA-fed heifers. In Exp. 2, 42 yearling steers (371.8 ± 0.8 kg; six pens) were fed LVA or HVA for ad libitum intake for 105 d. No treatment differences were observed. In Exp. 3, 144 early weaned (69.8 ± 1.9 d) steers (184.8 ± 1.6 kg; 18 pens) were fed ad libitum with VA treatments (LVA or HVA), were program-fed 1.27 kg/d throughout, or were fed 0.91 kg/d for 140 d then were fed ad libitum for 280.1 ± 3.5 d. Serum was collected three times during the experiment. Program-fed steers had less (P<0.05) ADG, increased days on feed, and improved marbling. Intermediate and final ROL were greater for HVA-fed steers. Intake restriction (15%) or program feeding (1.27 kg/d) tended to improve feed efficiency without altering carcass merit. Finishing phase intakes of VA at 3.3 times NRC (1996) recommendations increased ROL, but did not affect marbling in Angus × Simmental feedlot cattle.