Effect of low vitamin A diets with high-moisture or dry corn on marbling and adipose tissue fatty acid composition of beef steers

¹ Department of Animal Sciences, The Ohio State University, Wooster 44691
² Department of Food Science and Technology, The Ohio State University, Columbus 43210

^* To whom correspondence should be addressed. E-mail: loerch.1{at}osu.edu.

	Abstract

Angus-cross steers (n = 165; 295 ± 16 kg) were used evaluate the effect of low vitamin A diets with high-moisture corn (HMC) or dry corn (DC) on marbling and fatty acid composition. Steers were allotted to 24 pens (7 steers/pen) such that each pen had the same average initial BW. Treatments were randomly allotted to the pens. The experiment had a completely randomized design with a 2 x 2 factorial arrangement of treatments: low vitamin A (Lo, no supplemental vitamin A) and HMC (LoHMC); LoDC; high vitamin A (Hi, supplemented with 2,200 IU/kg DM) and HMC (HiHMC); and HiDC. Diets contained 76% corn, 10% corn silage, 11% protein supplement, and 3% soybean oil (DM basis). Samples of feed ingredients were collected for carotenoid analysis. Blood samples were collected for serum retinol determination. Steers were harvested after 145 d on feed. Carcass characteristics and LM composition were determined. Samples from the s.c. fat depot were analyzed for fatty acid composition. High-moisture corn had a greater vitamin A content based on its carotenoid content than DC (614 vs. 366 IU/kg DM, P < 0.01). No vitamin A x corn type interactions were detected for feedlot performance, carcass characteristics, or serum, s.c. fat, or liver retinol concentration. Average daily gain, DMI, and G:F were not affected by vitamin A (P > 0.05). Marbling score and USDA quality grade were greater (P < 0.05) in Lo vs. Hi steers. Hot carcass weight, back fat, and yield grade were not affected by the treatments (P > 0.05). Vitamin A and corn type did not affect LM composition (DM, ash, CP, and ether extractable fat, P > 0.05). Vitamin A supplementation increased (P < 0.06) serum retinol on d 112 and 145 and increased (P < 0.01) liver retinol at harvest (Lo = 38.7 vs. Hi = 102.9 µg/g). The s.c. fat retinol concentrations were less (P < 0.01) for Lo (0.8 µg/g) than for Hi (1.4 µg/g) at harvest. Cell diameter of adipocytes in the i.m. depot was not affected by dietary vitamin A (P > 0.05). A vitamin A x corn type interaction was observed (P < 0.05) in the s.c. fat cellularity. Feeding HMC increased the number of cells/mm² when Lo diets were fed (LoHMC = 128 vs. LoDC = 100 cells/mm², P < 0.05), but when Hi diets were fed, cellularity was not affected (HiHMC = 109 vs. HiDC = 111 cells/mm², P > 0.05). The CLA content of adipose tissue was not affected by the treatments. Regardless of the corn type used, feeding low vitamin A diets for 145 d to Angus-cross steers increased marbling and quality grade without affecting yield grade, animal health, or performance.

Key Words: Beef, Marbling, Corn, Vitamin A