Ruminal Availabilities of Protein and Starch: Effects on Growth and Ruminal and Plasma Metabolites of Dairy Calves,

Abstract Newborn Holstein calves (n = 75) were blocked by date of birth and sex and assigned randomly to one of eight isonitrogenous starters that contained protein and starch sources of different ruminal availabilities. Soybean meal or soybeans roasted to an exit temperature of 146°C, raw or conglomerated corn, and urea at 1% of DM or no urea were used in a 2 × 2 × 2 factorial arrangement. The conglomeration process consisted of grinding the grain, adding water, pelleting the mixture, and roasting, which increased the degree of starch gelatinization fivefold. Starters were fed for ad libitum intake from 0.5 to 8 wk. Urea supplementation of conglomerated corn starters depressed performance, but the depression was greater when conglomerated corn was used with soybean meal than when it was used with roasted soybeans. Ruminal NH 3 and plasma urea increased with increased RDP in starters, but the response varied according to corn type and soy protein source. Urea supplementation depressed plasma Lys, doubled plasma Cit with soybean meal and conglomerated corn starters, but depressed plasma Cit with roasted soybeans and conglomerated corn starters. Conglomerated corn depressed plasma Val and Gly, and roasted soybeans increased plasma Phe. Performance was similar when calves consumed starters containing ruminally synchronous or asynchronous CP and starch sources.