Influence of Bos indicus crossbreeding and cattle age on apparent utilization of a high-grain diet

Ten Bos indicus x MARC III (initial BW = 303 +/- 25 kg) and 10 MARC III (in itial BW = 322 +/- 16 kg) steers were used in a 2 x 2 factorial design to d etermine whether cattle age or Bos indicus crossbreeding influence site of digestion of a high-grain diet. Initially, five Bos indicus x MARC III and five MARC III steers were fitted with duodenal cannulas and adapted to a 95 % concentrate diet that was offered for ad libitum consumption for a 237-d feeding period (calves). During the feeding period, duodenal and fecal samp les were collected during 4-d periods beginning on d 14, 67, 137, and 228. The remaining 10 steers were fed a forage-based diet for a targeted daily g ain of .6 to .7 kg for 210 d (yearlings). Following this period, yearling s teers were duodenally cannulated and adapted to the 95% concentrate diet. Y earling steers had ad libitum access to feed for 165 d, and samples were co llected during 4 d periods beginning on d 13, 42, 102, and 159. Dry matter intake was 9.8 and 7.6 kg/d and daily gain was 1.35 and 1.16 kg in yearling s and calves, respectively. Apparent OM digestion in the stomach was greate r (P < .01) in yearlings than in calves. In contrast, postruminal disappear ance as a percentage of OM intake was greater (P = .05) in calves than in y earlings. Duodenal flows of total N, microbial N, nonmicrobial N, and total amino acids and total tract N digestibility were not affected (P > .05) by age or Bos indicus crossbreeding. Fecal N excretion was greater (P < .01) in yearlings than in calves. Results of this experiment suggest little effe ct of Bos indicus influence on utilization of a high-grain diet. However, m ore feed is digested in the rumen of yearlings than of calves consuming a h igh-grain diet.