Effects of vitamin A supplementation and weaning age on serum and liver retinol concentrations, carcass traits, and lipid composition in market beef cattle.

Angus crossbred steers (n=48) were either early-weaned (EW) at 137 days or weaned at a traditional age (TW) of 199 days to determine effects of weaning age and dietary vitamin A on serum and liver retinol, carcass traits, and lipid composition. Steers from both weaning ages were allotted to receive either 42,180IU vitamin A/day (HA) or no supplemental vitamin A (NA). Early-weaned and TW steers consumed vitamin A treatments for 235 and 175 days, respectively. Serum and liver retinol of HA steers were dramatically higher (P<0.01) than those of NA steers at the end of finishing. Steers were harvested in two groups 35 days apart at an average ultrasound 12th rib fat thickness of 1.0cm. Live and HCW were similar (P>0.10) between NA and HA steers, but HA steers had numerically greater (P⩾0.10) fat thickness (1.05 vs. 0.87cm). Marbling score and %IMF fat were numerically (P>0.10) higher for EWNA than EWHA steers. Ratio of marbling score/12th rib fat thickness was greater (P=0.08), and ratios of either marbling or %IMF per unit of 12th rib fat thickness, days on finishing diet, unit of HCW, and tenth of yield grade consistently favored steers fed NA, particularly EW steers. Proportions of serum fatty acids changed (P<0.05) during finishing; proportions of individual fatty acids of the longissimus muscle did not change. Restricting vitamin A during finishing has potential to increase carcass marbling and to decrease waste fat, particularly for EW.