Effect of protein source and grain type on finishing calf performance and ruminal metabolism.

A finishing trial and a metabolism trial were conducted to evaluate sources of supplemental protein in dry-rolled corn (DRC) and dry-rolled grain sorghum (DRGS) diets fed to large-framed calves and to determine effects of grain and protein source on ruminal metabolism. In Exp. 1, 144 Charolais crossbred steer and heifer calves (BW = 269 +/- 3 kg) were used in a randomized complete block design and fed (199 d) DRC or DRGS diets supplemented with urea or urea plus a 60:40 combination (CP basis) of blood meal (BM) and feather meal (FTH). Calves supplemented with urea-BM/FTH were more efficient (P < .05) during the first 41 d of the trial than were calves supplemented with urea alone. After 41 d, daily gain and feed efficiency were not affected (P > .2) by source of protein. The NRC metabolizable protein (MP) requirements accurately predicted response to urea-BM/FTH. In Exp. 2, five ruminally cannulated steers (BW = 721 +/- 20 kg) were used in a 5 x 5 Latin square design and fed (on an ad libitum basis) diets similar to those used in Exp. 1. An additional treatment of DRC supplemented with soybean meal (SBM) was included. Rate (P < .01) and extent of 12-h (P = .14) and 18-h (P < .05) in situ N disappearance of SBM, BM, FTH, DRC, DRGS, and corn silage were greater when diets were supplemented with urea-BM/FTH or SBM. Estimates of escape N (percentage of total N) were 52.3, 93.3, 91.7, 65.7, 63.6, and 23.2% for SBM, BM, FTH, DRC, DRGS, and corn silage, respectively. Finishing calves supplemented with urea were deficient in MP during the early finishing period (0 to 41 d) but were adequate in MP from d 42 to slaughter. Supplementing urea-BM/FTH improved feed efficiency when MP was limiting but not when MP was adequate.