PROTEIN SUPPLEMENTS FOR CORN-SILAGE DIETS AND THEIR EFFECT ON SUBSEQUENT GROWTH AND CARCASS CHARACTERISTICS IN BEEF-CATTLE

Ninety-six Brahman crossbred steers (187 +/- 3.9 kg) were used to evaluate protein supplements in corn-silage growing diets for 140 d. The following treatments were used: 1, control (7.9% crude protein (CP)); 2, urea (10.3% CP); 3, dehydrated alfalfa (10.0% CP); or 4, soybean meal (SBM) (10.6% CP). Steers were then fed a common finishing diet (80% com) with 13.4% CP for 120 d. Steers fed the control diet had lower levels of plasma-urea nitrogen, consumed less feed, gained less weight and utilized feed less efficiently than those fed supplemented diets (P < 0.05). Steers fed SBM gained weight faster than those fed urea (P < 0.05), though feed/gain ratios were similar. Although control steers exhibited compensatory growth during the 120-d finishing period, re-alimentation was not complete, and their overall gain was lowest at the end of the 260-d study (P < 0.05). Cattle fed the low-protein growing diet also had lighter carcasses, smaller loin eye area and less backfat and marbling than steers fed protein supplements (P < 0.05). Carcass characteristics were similar for the three protein supplements. These results demonstrate that urea equalled SBM and dehydrated alfalfa as a protein source in a com-silage growing diet as measured by overall performance and carcass characteristics at the end of 120 d re-alimentation on a finishing diet. However, the negative effects of protein deprivation during the 140-d growing period were not completely overcome after a 120-d finishing period.