Abomasal infusion of corn starch and ß-hydroxybutyrate in early-lactation Holstein-Friesian dairy cows to induce hindgut and metabolic acidosis.

The objectives of this study were to induce hindgut and metabolic acidosis via abomasal infusion of corn starch and ß-hydroxybutyrate (BHB), respectively, and to determine the effects of these physiological states in early-lactation dairy cows. In a 6 × 6 Latin square design, 6 rumen-fistulated Holstein-Friesian dairy cows (66 ± 18 d in milk) were subjected to 5 d of continuous abomasal infusion treatments followed by 2 d of rest. The abomasal infusion treatments followed a 3 × 2 factorial design, with 3 levels of corn starch and 2 levels of BHB. The infusions were water as control, 1.5 kg of corn starch/d, 3.0 kg of corn starch/d, 8.0 mol BHB/d, 1.5 kg of corn starch/d + 8.0 mol BHB/d, or 3.0 kg of corn starch/d + 8.0 mol BHB/d. A total mixed ration consisting of 35.0% grass silage, 37.4% corn silage, and 27.6% concentrate (on a dry matter basis) was fed at 90% of ad libitum intake of individual cows. The experiment was conducted in climate respiration chambers to facilitate determination of energy and N balance. Fecal pH decreased with each level of corn starch infused into the abomasum and was 6.49, 6.00, and 5.15 with 0.0, 1.5, and 3.0 kg of corn starch/d, respectively, suggesting that hindgut acidosis was induced with corn starch infusion. No systemic inflammatory response was observed and the permeability of the intestine or hindgut epithelium was not affected by the more acidic conditions. This induced hindgut acidosis was associated with decreased digestibility of nutrients, except for crude fat and NDF, which were not affected. Induced hindgut acidosis did not affect milk production and composition and energy balance, but increased milk N efficiency. Abomasal infusion of BHB resulted in a compensated metabolic acidosis, which was characterized by a clear disturbance of acid-base status (i.e., decreased blood total CO2, HCO3, and base excess, and a tendency for decreased urinary pH), whereas blood pH remained within a physiologically normal range. Abomasal infusion of BHB resulted in increased concentrations of BHB in milk and plasma, but both remained well below the critical threshold values for subclinical ketosis. Induced compensated metabolic acidosis, as a result of abomasally infused BHB, increased energy retained as body fat, did not affect milk production and composition or inflammatory response, but increased intestinal permeability.

Asynchronous supply of indispensable amino acids reduces protein deposition in milk-fed calves.

A balanced supply of indispensable amino acids (AA) is required for efficient protein synthesis. Different absorption kinetics (e.g., free vs. protein-bound AA) may, however, create asynchrony in postabsorptive availability of individual AA, thereby reducing the efficiency of protein deposition. We studied the effects of AA asynchrony on protein metabolism in growing, milk-fed calves. In 2 experiments, each with a change-over design including 8 calves, a milk replacer deficient in Lys and Thr was used. In Expt. 1, L-Lys and L-Thr were parenterally supplemented, either in synchrony (SYN), asynchrony (ASYN), or partial asynchrony (PART) with dietary AA. In Expt. 2, l-Lys and l-Thr were orally supplemented, either in SYN or ASYN with dietary AA. In Expt. 1, digested protein was used less efficiently for growth for ASYN (31.0%) than for SYN (37.7%), with PART being intermediate (36.0%). Indicator AA oxidation tended (P = 0.06) to be higher for ASYN. In Expt. 2, the efficiency of protein utilization was lower for ASYN (34.9%) than for SYN (46.6%). Calves spared AA from oxidation when the limiting AA were provided in excess after a short period (<24 h) of deprivation. Restoring AA balance by parenteral supplementation resulted in a 19% lower efficiency of digestible protein utilization than by oral supplementation, likely caused by splanchnic oxidation of imbalanced AA in excess to Thr. In conclusion, asynchronous availability of individual indispensable AA reduces the efficiency by which digested protein is retained in milk-fed calves. Furthermore, an AA imbalance in the splanchnic tissues may result in disproportionate AA oxidation.

Body fat deposition does not originate from carbohydrates in milk-fed calves.

Milk-fed heavy calves utilize dietary protein with a low efficiency and often develop hyperglycemia and insulin resistance. Distributing the daily nutrient intake over an increasing number of meals increases protein deposition and improves glucose homeostasis. Therefore, we examined effects of feeding frequency (FF) and feeding level (FL) on the diurnal pattern of substrate oxidation and on the fate of dietary carbohydrates in milk-fed heavy calves. Eighteen milk-fed calves weighing 136 +/- 3 kg were assigned to FF (1, 2, or 4 meals daily) at each of 2 FL (1.5 or 2.5 times maintenance), except for calves at FF1 (only at a low FL). Urea, leucine, and glucose kinetics were assessed for each treatment by use of [(13)C]urea, [1-(13)C]leucine, [U-(13)C], and [2-(13)C]glucose, respectively. FF altered the diurnal pattern, but not the total, of urea production production. Although urea production correlated well with nitrogen retention, oxidation of oral l-[1-(13)C]leucine did not. Dietary glucose was almost completely oxidized (80% based on [(13)C]glucose and 94% from indirect calorimetry measurements) regardless of FL. Fatty acid synthesis from glucose appeared to be negligible based on similar recoveries of (13)CO(2) from orally supplied [U-(13)C]glucose and [2-(13)C]glucose. The increased fat deposition at the higher FL originated almost exclusively from greater transfer of fatty acids to body lipid stores. These findings contrast with both glucose and lipid metabolism in growing pigs and indicate that alternative adaptive mechanisms operate in heavy milk-fed calves.

Synchronizing the availability of amino acids and glucose decreases fat retention in heavy preruminant calves.

Effects of synchronizing the availability of amino acids and glucose within a day on protein and energy metabolism were studied in heavy preruminant calves. Thirty-six preruminant calves (148 +/- 1.6 kg body weight) were assigned to 1 of 6 degrees of nutrient synchrony (SYN, 1-6) and to 1 of 2 meal sequences (i.e., the high-protein meal in the morning or in the evening). Calves at SYN 1 received 2 balanced meals: one at 0600 and one at 1800. Nutrient synchrony decreased stepwise from SYN 1 to SYN 6 in which calves received 85% of the daily protein supply in 1 meal. The digestible energy intakes at 0600 and 1800 were equal between treatments. Daily intakes of all nutrients and dietary ingredients were identical for all treatments. Calves were housed individually in respiration chambers. Apparent fecal nutrient digestibility and nitrogen and energy balances were measured. Apparent nutrient digestibility decreased when >71% of the dietary protein was fed in one meal. Nutrient synchrony did not affect the efficiency of digestible protein utilization in calves at a identical digestible nutrient intake. Heat production decreased from 691 to 629 kJ/(kg(0.75) x d) (P < 0.05) and energy retained as fat increased from 116 to 184 kJ/(kg(0.75) x d) (P < 0.01) with decreasing nutrient synchrony. Meal sequence did not affect any of the traits. In conclusion, synchronizing the availability of amino acids and glucose within a day did not increase the efficiency of protein utilization but substantially decreased fat retention in heavy preruminant calves.