Effect of dietary vitamin A concentration and roasted soybean inclusion on marbling, adipose cellularity, and fatty acid composition of beef

¹ Department of Animal Sciences, The Ohio State University, Wooster, OH

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

	Abstract

A feedlot trial was conducted to determine the effect of dietary vitamin A concentration and roasted soybean (SB) inclusion on carcass characteristics, adipose tissue cellularity, and muscle fatty acid composition. Angus-crossbred steers (n = 168; 295 ± 1.8 kg) were allotted to 24 pens (7 steers each). Four treatments were investigated: No supplemental vitamin A - No roasted soybeans (NANS); No vitamin A - Roasted soybeans (20% of the diet) (NASB); With supplemental (2,700 IU/kg) vitamin A - No roasted soybeans (WANS); With supplemental vitamin A - Roasted soybeans (WASB). Diets included high moisture corn, 5% corn silage, 10 to 20% supplement, and 20% roasted soybean in SB treatments. Calculated vitamin A concentration in the basal diet was < 1,300 IU/kg DM. Blood samples (2 steers/pen) were collected for serum vitamin A determination. Steers were harvested after 168 d on feed. Carcass characteristics and LM composition were determined. Fatty acid composition of LM was analyzed and adipose cellularity in the i.m. and s.c. depots was determined. No vitamin A x SB interactions were detected (P > 0.10) for cattle performance, carcass composition, or muscle fatty acid composition. Low vitamin A diets (NA) did not affect (P > 0.05) ADG, DMI, or G:F. Quality grade tended (P = 0.07) to be greater in NA steers. Marbling scores and the percentage of carcasses grading Ch- were 10% greater for NA steers, although these trends were not significant (P = 0.11 and 0.13, respectively). Back fat thickness and yield grade were not affected (P > 0.26) by vitamin A supplementation. Composition of the LM was not affected (P > 0.15) by vitamin A or SB supplementation. Serum retinol at harvest was 44% lower (P < 0.01) for steers fed NA than for steers supplemented with vitamin A (23.0 vs. 41.1 µg/dL). A vitamin A x SB interaction occurred (P < 0.05) for adipose cellularity in the i.m. depot. When no SB were fed, vitamin A supplementation decreased cell density and increased cell size. However, when SB were fed, vitamin A supplementation did not affect adipose cellularity. Adipose cellularity at the s.c. depot was not affected (P > 0.18) by vitamin A or SB treatments. Fatty acid profile of the LM was not affected by vitamin A (P > 0.05), but SB increased (P < 0.05) PUFA (7.88 vs. 4.30 g/100 g). It was concluded that feeding NA tended to increase marbling without affecting back fat and yield grade. It appeared that NA induced hyperplasia in the i.m. but not in the s.c. depot.

Key Words: Beef, Marbling, Vitamin A, Roasted Soybeans