Effects of the forage content of the winter diet on the growth performance and carcass quality of steers finished on mountain pasture with a barley supplement

Abstract

Eighteen Parda de Montaña steers (366 kg liveweight, 10 months of age) received diets of either forage (F; lucerne hay + straw) or forage and concentrate (FC; lucerne hay + straw + barley) during the winter feeding period, which lasted 118 days. Thereafter, steers continuously grazed in meadows in a dry mountain area until the end of the grazing period in September (160–167 days) and received 4.1 kg DM barley per head for the final 103–110 days of the grazing season. The steers that received the FC winter diet were heavier (491 vs 457 kg, respectively; P < 0.05) and had deposited more fat (7.2 vs 5.8 mm, P < 0.05) and muscle (63 vs 54 mm, P < 0.05) at the end of the winter than the steers that received the F winter diet. During the grazing period, the steers from both groups had similar weight gains (0.728 and 0.756 kg/day for FC and F diet, respectively). At slaughter, the steers from both groups were of similar age (590 vs 599 days, for FC and F diet, respectively) and had similar liveweights (560 vs 539 kg), muscle depths (54 vs 63 mm) and subcutaneous fat thicknesses (7.3 vs 7.2 mm). The serum leptin concentration differed only at the end of the winter period, when steers on the FC diet had higher leptin concentrations than did steers on the F diet (P < 0.05), reflecting differences in fatness. The carotenoid concentration in the plasma during the winter feeding period was higher in steers on the F than on the FC winter diet, but this difference was not seen during the grazing period. Carcasses from steers on the FC winter diet were heavier (324 vs 300 kg; P < 0.05) and had a higher dressing percentage (57.3% vs 56.1%, P < 0.05) than those reared on the F winter diet, but the fatness and conformation scores were similar between the groups. The percentages of fat, muscle and bone in the commercial dissection and 10th rib dissection did not differ between the winter diet groups. In conclusion, the differences resulting from the winter feeding period disappeared after the grazing period, and the carcass quality did not differ between the diets. Therefore, both strategies are equally technically advisable.