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Total blood flow from an intestinal segment (TBF) was altered to determine effects on blood flow at the absorptive site (ASBF) and lysine absorption. Venous blood flow was restricted using a peristaltic pump to 20, 35, 50, 65, and 80% of the initial unrestricted rate. Lysine absorption and ASBF were determined from recovery of 14C and 3H in blood from intestinally perfused [14C]L-lysine and 3H2O, respectively. Fluid flux in the intestinal lumen was estimated from the difference in polyethylene glycol concentrations in luminal infusate and effluent. Restriction of TBF proportionally reduced ASBF, which composed 3 to 6% of TBF. Lysine absorption was reduced linearly during reduction of TBF. Fluid absorption varied among calves but was independent of TBF. Differences between loss of radioactive marker from perfusate and recovery in blood suggested a loss of 3H2O from the intestinal segment that was independent of TBF. Changes in blood flow to the small intestine may affect nutrient absorption in ruminants.

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Holstein bull calves, 8 to 12 wk of age, were anesthetized with halothane gas. An approximate 20-cm section of small intestine, 60 to 90 cm proximal to the ileocecal junction was clamped to isolate blood circulation to a single set of arcuate vessels and to form an intestinal segment fitted for infusion and drainage. The vein was catheterized to allow total venous collection. Donor blood was transfused via jugular vein to replace venous drainage. This technique was evaluated in four calves by exposing the lumen to eight replications (12 or 20 min incubation, 30-min wash with 39 C saline) of 16 mM L-Met (14C-labeled). Time course appearance of Met in venous blood indicated similar rates and patterns of absorption for individual calves. There were no clinically significant alterations in jugular blood chemistry profiles across replications. Four calves were used to evaluate the effect of three isotonic perfusion media (saline, Krebs-Ringer bicarbonate and M-199 tissue culture media) on Lys and Met absorption. Venous flow rates and absorption of Lys were faster with Krebs buffer than with other media. Perfusate medium did not influence venous flow rates or absorption of Met. Effect of restricting venous flow on absorption of Lys and Met was evaluated in two calves. Flow was alternately controlled (6.5 ml/min) or allowed to flow freely (mean = 12.2 ml/min). Restricting flow decreased steady-state absorption. Light and scanning microscopy indicated maintenance of mucosal tissue integrity throughout 8 h of anesthesia. Results demonstrate validity of the in situ technique to study nutrient absorption in the young bovine.

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A neonatal calf with anuria, uroperitoneum, azotemia, hyperphosphatemia, and hyperkalemia was found to have a congenital urethral obstruction. The calf had a concomitant infection of the internal umbilical remnants. Surgical intervention corrected both conditions.

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Effects on total lactation performance of varying ration crude protein (15.3 vs. 13.6% of dry matter) and nitrogen solubility (35 vs. 45% of total nitrogen) in early lactation was studied using 57 pluriparous Holstein cows. Grain was fed according to production so as to minimize change in body weight throughout lactation. Forages high in nitrogen solubility, corn and grass silages, were fed free-choice. Percent concentrate in ration dry matter was highest (64%) 5 to 8 wk postpartum and lowest (3%) 33 to 44 wk postpartum. Protein and nitrogen solubility were varied by formulating four protein supplements fed as 10% of the grain allocation, so differences in treatments applied narrowed as lactation progressed. Cows fed the medium-protein diets produced 196 kg more milk than those receiving low-protein diets, but their peak daily milk yield was only .6 kg higher. Cows receiving rations with reduced nitrogen solubility produced 347 kg more milk than those fed the higher solubility diets, but their peak daily milk yield was 1.0 kg lower. Income above fed cost for the lactation was highest and postpartum loss in body weight was least for cows receiving medium-protein and low-solubility rations in early lactation, but no differences were significant. Both milk yield (38.3 to 40.6 kg) and total dry matter intake (3.74 to 3.91% body weight) means were maximum 6 to 7 wk postpartum, but lactation performance was not proportional to peak milk yield. When cows are fed to minimize body fat mobilization, response to increased protein in the diet is small. Reducing nitrogen solubility of silage-based diets increased milk produced per unit grain fed. There were no adverse effects of treatments on breeding efficiency or herd health.

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In a 1-month-old calf, intestinal strangulation developed when a jejunal segment wrapped around a bandlike adhesion between the greater omentum and an abscess of the left umbilical artery. Signs included abdominal distention, cessation of defecation, and purulent inflammation of the external umbilical stalk. Despite vigorous care, the calf died of shock 4 hours after admission.

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Holstein bull calves weaned at 4 wk of age were assigned to one of three replicated 4 X 4 Latin squares at 5 to 6 wk. Trials were abomasal infusion of 0, .30, .60, and either 90 (Trials 2 and 3) or 1.20 g (Trial 1) L-methionine/kg pelleted starter ration consumed. In Trials 1 and 2, ration ingredients of the ration contributed the following percentages of total crude protein: corn meal 39, alfalfa meal 48, and soybean meal 12; dry matter of rations contained 13.6 and 13.9% crude protein and .26 and .32% sulfur. Infusion of .60 g methionine in Trial 1 tended to depress excretion of nitrogen in urine and increase nitrogen retention. In Trial 2, urine nitrogen excretion and retained nitrogen responded in a quadratic fashion; infusion of .30 and .60, and either .90 (Trials 2 and 3) or 1.20 g (Trial 1) L-methionine/kg pelleted starter ration consumed. In Trials 1 and 2, ingredients of the ration contributed the following percentages of total crude protein: corn meal 39, alfalfa meal 48, and soybean meal 12; dry matter of rations contained 13.6 and 13.9% crude protein and .26 and .32% sulfur. Infusion of .60 g methionine in cretion 9%. Relationship between plasma methionine and infused methionine was linear for all trials. Methionine is the first limiting amino acid for early-weaned calves fed complete pelleted rations based on corn and either alfalfa or soybean proteins.

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Effects of weaning age (4 and 8 wk) and ration (complete pelleted starter and unpelleted starter plus alfalfa-grass hay) on development of ruminal function were tested in a split-plot design. Maturity of ruminal function was estimated by the contribution of bacterial nitrogen to total nitrogen reaching the abomasum, essential amino acid composition of bacterial and abomasal protein, and ruminal volatile fatty acid concentrations. Sixteen Holstein bull calves were fitted with rumen and abomasal cannulas by 1 wk of age, and ingesta were sampled twice weekly from 2 to 11 wk of age. Contribution of bacterial nitrogen to total nitrogen in abomasal contents was similar to that of mature ruminants by 5 and 7 wk of age for calves weaned at 4 and 8 wk of age, respectively. Concentrations of ruminal volatile fatty acids indicative of mature ruminal function were reached by 5 wk of age. Pattern of essential amino acids in bacterial cells of the rumen was not affected by age, weaning age, or ration and was similar to that of mature ruminants. Analysis of abomasal digesta indicated no effect of starter ration and no effect of age or weaning age on the relative proportion of essential amino acids except lysine and arginine. Lysine decreased and arginine increased linearly from 2 wk until weaning.

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Three abomasal infusion trials were to determine the first-limiting amino acid for nitrogen retention of postweaned Holstein bull calves fed a starter ration based on cereal by-product feeds. Ration ingredients contributed the following percentages of total amino acids: wheat middlings 38, brewer's grains 24, hominy feed 21, oat hulls 10, distiller's grains 6, and molasses 1. Dry matter of the pelleted ration contained 13 to 14% crude protein and .23 to .26% sulfur. Each trial was a replicated 4 x 4 Latin square with 9-day periods. Calves were weaned at 4 wk and infusions initiated at 5 to 6 wk of age. Abomasal infusion of the 10 essential amino acids, an isonitrogenous quantity of an equimolar mixture of alanine, asparagine, glutamate, glycine, and serine, or an isocaloric quantity of glucose indicated that essential amino acid(s) rather than nonspecific nitrogen or energy was limiting protein synthesis. Quadratic responses in urine nitrogen excretion and retained nitrogen occurred when 0, .3, .6, and 1.2 g L-methionine/kg starter ration were infused. Greatest responses occurred with .6 g methionine, which increased retained nitrogen 11 and 19% and decreased urine nitrogen 7 and 10%. The relationship between infused methionine and plasma methionine was linear. Infusions in all trials had no effect on digestibility of energy and nitrogen.

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