Effects of supplemental protein sources during the grazing period on performance, ruminal characteristics and blood constituents in early weaned growing Wagyu steer calves

We investigated the effects of grazing and supplemental protein sources during the grazing period on growth performance, ruminal characteristics and blood constituents in 15 growing Wagyu steer calves weaned at 3 months of age. Each animal was allotted one of three treatments: (1) GSBM, soybean meal (SBM) supplemented as a protein source during a grazing period; (2) GCGM, corn gluten meal (CGM) supplemented as a protein source during a grazing period; or (3) NG, no grazing, in which steers were fed hay and GSBM concentrate only. The estimated rumen undegradable protein (RUP) concentration of CGM was higher than that of SBM. High RUP supplementation during the grazing period did not influence feed intake or growth performance. Compared with the NG treatment, the average daily gain in GSBM and GCGM calves was significantly depressed (P < 0.05). Bodyweight/withers height ratio in the NG calves tended to be greater than in the GSBM and GCGM calves. Final paunch girth/heart girth ratio in the GSBM and GCGM calves was significantly greater (P < 0.05) than in the NG calves. Supplementation with CGM did not influence ruminal ammonia nitrogen and blood constituents. These results indicate that CGM supplementation during the grazing period did not enhance the growth of Wagyu calves because the CGM diet probably did not elevate the metabolizable protein supply to the grazing calves above that of the SBM diet in our conditions.