Two experiments were conducted to assess the effects of corn grain processing on performance, ruminal fermentation, and starch digestion in early lactation dairy cows. Diets were based on wilted alfalfa silage and high moisture or dry corn grain that was either ground or rolled. Thirty-four cows (17 multi-parous) were used to measure effects on intake and lactational performance in a free-stall environment during wk 2 to 15 postpartum. Grinding increased dry matter intake, particularly for cows fed diets containing dry corn, and tended to increase yields of milk, protein lactose, and SNF. Cow performance was not affected by the moisture content of the corn grain. In the digestion experiment, six cows (43 d of lactation) with ruminal, duodenal, and ileal cannulas were used to measure ruminal and intestinal digestion. Search digestion in the rumen and small intestine was greater for high moisture corn, but disappearance of starch in the large intestine was greater for dry corn. Both the grinding process and the high moisture content of the corn increased starch digestibility in the total tract. Flow of microbial N in the duodenum was not affected by treatment. High moisture corn increased starch digestion in the rumen and total tract and enhanced ruminal fermentation as indicated by increased volatile fatty acids and decreased NH3 concentrations in the rumen. In the production experiment, however, only grinding improved the value of corn; ensiling at high moisture content had little effect.

The objective of this study was to quantify changes of net nutrient metabolism by portal-drained viscera (PDV) and liver of four beef steers (253 +/- 7 kg) in response to combinations of ruminal (R) or abomasal (A) infusions of cornstarch (S) and casein (C). The four treatments in a Latin square design were SACA, SACR, SRCA, and SRCR. Steers were fed alfalfa hay (DMI = 4 kg/d) as a basal diet in 12 equal meals delivered every 2 h and they received continuous infusion of S (800 g/d) and C (200 g/d) in 11-d periods. Digestibilities of DM, N, NDF, and starch, ruminal outflow of liquids and DM, and energy and N retention were less (P < .05) for SA than for SR. Net ammonia and glucose release from PDV were greater (P < .01) for SA than for SR. Net total VFA, acetate, and beta-hydroxybutyrate release from PDV and total splanchnic acetate and beta-hydroxybutyrate release were greater (P < .05) for SR than for SA, but starch infusion site had no effect (P > .10) on net urea N transfer or alpha-amino N release by PDV. Net release of ammonia N, propionate, and total VFA by PDV and uptake of urea N by PDV were greater for CR than for CA, but net alpha-amino N release by PDV and total splanchnic tissues were greater for CA than for CR (P < .05). Summation of energy supply by PDV indicated no difference in total supply among the treatments, but relative contribution of energy sources was affected by infusion site. Energy release by PDV per unit of DE intake was .68 and .66 for SA and SR, respectively. Net release of glucose by PDV was greater for SACA than for SACR (P < .05). These results suggest that site of digestion of starch and casein varies the relative contribution of nutrients to energy supply by visceral tissues and therefore varies N use in beef steers.

The effect of ruminal or abomasal starch infusion on milk yield and glucose metabolism of early lactation cows was measured. Four cows were continuously infused in the rumen or abomasum with partially hydrolyzed starch (1500 g/d) or were not infused (control) for three 14-d periods during wk 4 to 12 postpartum. Milk yield averaged over 40 kg/d throughout the experiment. Milk and milk lactose yields tended to increase when starch was infused and DMI was decreased, regardless of the site of infusion. Starch infusion increased mean insulin concentration and tended to decrease the concentration of serum nonesterified fatty acids. Ruminal starch infusion did not affect glucose irreversible loss rate but tended to increase glucagon concentration and decrease glucose oxidation. The increased milk yield that occurred when starch was infused ruminally relative to the milk yield of control cows could be a result of increased microbial protein supply or increased energy availability. Compared with ruminal starch infusion, abomasal starch infusion tended to increase the irreversible loss rate of glucose and to increase glucose oxidation. Abomasal infusion tended to increase plasma insulin concentration and to decrease the nonesterified fatty acid concentration relative to ruminal infusion. Infusion of starch abomasally resulted in increases of most uses of glucose, including milk lactose production, glucose oxidation, and the possible storage of glucose as body fat, which indicates that the early lactation dairy cow has a greater capacity for glucose metabolism than is provided by voluntary feed intake of average diets, but that not all available glucose is partitioned to the mammary gland. These data should be useful in testing current concepts and equations in nutritional and metabolic models of dairy cattle.