Effect of vitamin A restriction on carcass characteristics and immune status of beef steers

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

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

	Abstract

Sixty-eight Angus-based steers (224 ± 7.6 kg of BW) were used to evaluate the effects of a prolonged dietary vitamin A restriction on marbling and immuno-competency. Steers were allotted randomly to 1 of 2 treatments: LOW (no supplemental vitamin A); and HIGH (diet supplemented with 2,200 IU vitamin A/kg DM). Diets contained 60% high-moisture corn, 20% roasted soybeans, 10% corn silage, and 10% of a protein supplement. Steers were penned and fed individually. For the first 141 d, steers were program-fed to achieve a gain of 1.1 kg/d. The last 75 d of the experiment, steers were offered feed for ad libitum intake. At slaughter, serum and liver samples were taken to determine retinol content. To evaluate immuno-competency, on d 141, 10 steers per treatment were selected randomly and received an ovalbumen vaccine, and 21 d later steers were revaccinated. On d 182, blood samples were taken from vaccinated steers to determine serum antibody titers by ELISA. Steers were slaughtered after 216 d on feed. Carcass characteristics were determined and LM samples were taken for composition analysis. Subcutaneous fat samples were taken for fatty acid composition analysis. Performance (ADG, DMI, and G:F) was not affected by vitamin A restriction (all P > 0.10). Hot carcass weight, 12th-rib fat, and yield grade did not differ between LOW and HIGH steers (all P > 0.10). Marbling score (LOW = 574 vs. HIGH = 568, P = 0.79) and i.m. fat (LOW = 5.0 vs. HIGH = 4.7 % ether extractable fat, P = 0.57) were not increased by vitamin A restriction. Serum (LOW = 18.7 vs. HIGH = 35.7 µg/dL, P < 0.01) and liver (LOW = 6.3 vs. HIGH = 38.1 µg/g, P < 0.01) retinol levels were lower in LOW steers at slaughter. Response to ovalbumin vaccination was not affected by vitamin A restriction (LOW = 13.1 vs. HIGH = 12.8 titers_log2, P = 0.60). Slight changes in the fatty acid profile of steers were detected. A greater proportion of MUFA (LOW = 41.7 vs. HIGH = 39.9%, P = 0.03) and fewer SFA (LOW = 47.1 vs. 48.7, P = 0.03) were observed in vitamin A restricted steers. This suggests that vitamin A restriction may affect the activity of desaturase enzyme (desaturase activity index, LOW = 46.9 vs. HIGH = 44.9, P = 0.01). Feeding a low vitamin A diet for 216 d to Angus-based steers did not affect performance, marbling score, or animal health and immuno-competency. Slight changes in the fatty acid profile were observed suggesting that vitamin A restriction may have affected desaturase enzyme activity.

Key Words: beef, immunity, marbling, vitamin A