Review: Potential Effects of Vitamins A and D on Marbling Deposition in Beef Cattle

Seasonal variation in cattle grading Choice exists with percentages of carcasses grading higher in the spring and gradually declining throughout the summer with a low in October. Various nutritional or pharmacological agents have been shown to affect adipose conversion in vitro and in vivo. High (5 to 50 μM) levels of dietary fat-soluble vitamins, especially retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (D3), inhibit adipocyte development, specifically bovine marbling, while lesser (≤10 nM) levels actively stimulate this deposition. This review was conducted to highlight the regulatory effects of vitamins A and D on adipocyte differentiation and offer a potential explanation for seasonal fluctuation in beef quality grades. Serum retinol concentration was negatively correlated with beef marbling index. Steers consuming diets containing low vitamin A concentration exhibited less serum retinol and produced greater marbling scores compared with steers consuming high vitamin A diets. Seasonal variation in quality grade may be explained by previous intake of vitamin A from lush forages and/or vitamin D synthesis from long day sun exposure. Cattle placed in the feedlots in spring or early summer are commonly grazed on lush forages, fed during the long day-length months and marketed in the fall, coinciding with seasonal lows for quality grade. Excessive circulating levels of vitamins A and D diminished adipocyte hyperplasia, lessened marbling score, and may partially explain seasonal depressions in carcasses grading Choice. Further research is necessary to elucidate the timing and dietary level of vitamins A and D during the finishing period and their relationship to high quality beef production.