Ruminal metabolic development in calves weaned conventionally or early.

Eight neonatal bull calves were rumen fistulated and assigned to one of two weaning programs to study the effect of diet and weaning age on ruminal metabolic development. All calves were fed colostrum until 3 d of age and milk until weaning. Calves in the early weaning program were fed milk and a highly palatable, prestarter diet until they consumed 227 g/d and then a mixture of 227 g of prestarter and all the starter diet they would eat. Calves in this group were weaned at 4 wk of age. Calves in the conventional weaning program were fed milk and a starter diet and weaned at 6 wk of age. Eight ruminal samples were collected over 12 h from each calf at 1, 4, 8, and 12 wk of age. Ruminal fluid samples were analyzed for pH, VFA, NH3 N, and L(+)-lactate and D(-)-lactate concentrations. Calves weaned early had lower ruminal pH, higher total VFA concentration, and higher molar proportion of butyrate than conventionally weaned calves. Ruminal NH3 N and lactate concentrations were not significantly affected by the weaning program, although lactate tended to be higher in calves weaned early. Ruminal VFA concentration increased and NH3N concentration decreased with increased feed consumption by calves in both groups. Molar proportions of acetate, isobutyrate, and isovalerate decreased, and those of propionate increased with age in both groups. Apparently, ruminal metabolic development, as evidenced by changes in fermentation products, was faster in calves weaned early than in calves weaned conventionally.