Production, Management and the Environment: Systems, Economics, and Miscellaneous

Four rumen fistulated Holstein calves (BW 132.3 ± 1.61 kg) fed high concentrate diets (10 to 90, forage to concentrate ratio) were assigned to a 4 x 4 Latin square design to investigate the effects of nonstructural carbohydrate (barley or corn) and protein (soybean meal or sunflower meal) sources on ruminal fermentation and animal performance. The following 2 x 2 factorial arrangement of treatments (13.7% CP, 2.8 Mcal ME/kg DM) was used: 1) Barley-Soybean meal; 2) Barley-Sunflower meal; 3) Corn-Soybean meal and 4) Corn-Sunflower meal. Data were analyzed using the PROC MIXED procedure of SAS, main factors being nonstructural carbohydrate source, protein source and their interaction. Calf and period were considered random effects. Intake of DM was higher in the corn vs. barley based diets (P < 0.05), without affecting ADG (1.2 ± 0.12 kg/d). Consequently, feed efficiency was higher for the barley based diets. Average ruminal pH, total VFA and NH3N concentration were not affected by main factors (6.6 ± 0.14, 116.4 ± 5.27 mM and 5.9 ± 2.17 mg/dL, respectively). Total VFA per kg of DM intake was lower in the corn vs. barley based diets (20.07 vs. 25.42 mM/kg DMI, P = 0.02) and no significant effects were observed for the proportions of individual VFA. Nonstructural carbohydrate and protein sources did not affect total tract digestibility of DM and OM, estimated with chromium oxide (64.5 ± 2.67 and 65.1 ± 2.74 %, respectively). Feeding behavior, measured by scan sampling at 5 minute intervals, did not vary significantly among treatments. Calves spent 9.97, 2.11, 25.13 and 62.79% of the time eating, drinking, ruminating and resting, respectively. In conclusion, while nonstructural carbohydrate source affected intake, feed efficiency and total VFA per kg of DM intake, protein source did not affect these measurements.