RUMINAL AVAILABILITIES OF PROTEIN AND STARCH - EFFECTS ON GROWTH AND RUMINAL AND PLASMA METABOLITES OF DAIRY CALVES

Newborn Holstein calves (n = 75) were blocked by date of birth and sex and assigned randomly to one of eight isonitrogenous starters that co ntained protein and starch sources of different ruminal availabilities . Soybean meal or soybeans roasted to an exit temperature of 146 degre es C, raw or conglomerated corn, and urea at 1% of DM or no urea were used in a 2 x 2 x 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 five fold. Starters were fed for ad libitum intake from 0.5 to 8 wk. Urea s upplementation of conglomerated corn starters depressed performance, b ut the depression was greater when conglomerated corn was used with so ybean meal than when it was used with roasted soybeans. Ruminal NH3 an d plasma urea increased with increased RDP in starters, but the respon se varied according to corn type and soy protein source. Urea suppleme ntation depressed plasma Lys, doubled plasma Cit with soybean meal and conglomerated corn starters, but depressed plasma Cit with roasted so ybeans and conglomerated corn starters. Conglomerated corn depressed p lasma Val and Gly, and roasted soybeans increased plasma Phe. Performa nce was similar when calves consumed starters containing ruminally syn chronous or asynchronous CP and starch sources.