Vitamin A, Zfp423 and Intramuscular Adipogenesis in Beef Cattle

Marbling, or intramuscular fat, is one of the most important factors in the palatability of beef. Selection for lean muscle and rapid growth in beef cattle has negatively impacted marbling, making it critically important to develop methods to increase marbling and thus palatable beef. Previous studies have shown that vitamin A (VA) promotes the formation of new fat cells in skeletal muscle through an increase in the expression of Zinc finger protein (Zfp) 423, a key regulator of fat cell formation. We hypothesized that VA injection during the critical stage for formation of fat cells in muscle would enhance intramuscular adipogenesis and marbling through the expression of Zfp423. Angus bull calves (n = 26), in a Completely Randomized Design, were randomly allotted to three treatment groups at birth. The first group (n = 9) received no supplemental VA, while the second (n = 7) and third group (n = 10) were given 150,000 IU of VA and 300,000 IU of VA at both birth and one month of age, respectively. After weaning, calves were fed a backgrounding diet until 10 months of age then a high-concentrate feedlot diet until harvested at 14 months of age. Weaning weight and average daily gain during the backgrounding phase were linearly increased (P < 0.05) by VA level. Intramuscular fat of steers at 10 months of age, measured by ultrasound, quadratically increased (P < 0.05) with VA level from 4.0 to 4.9 % 0.26. Similarly, marbling score (small = 500, modest = 600) in the ribeye quadratically increased (584, 674 and 608 21.15 for the 0 IU, 150,000 IU and 300,000 IU treatment groups, respectively). Carcass back fat thickness quadratically increased (P < 0.05) with level of VA. However, yield grade quadratically decreased (P < 0.05) with VA where the high-level treatment had the lowest, or best, yield grade. Cattle that received VA had greater marbling, though further studies will need to evaluate an optimal amount as the mid-level treatment group had greater fat development and the high-level treatment group had greater muscling and higher average daily gain. Dietary VA enhanced intramuscular adipogenesis and marbling thereby improving meat quality.