Effect of intestinal blood flow on absorptive site blood flow and lysine absorption as examined in situ in Holstein calves.

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.

Amino acid limitation and flow to duodenum at four stages of lactation. 1. Sequence of lysine and methionine limitation.

Four Holstein cows with ruminal and duodenal cannulas were assigned to a 4 x 4 Latin square at each of four stages of lactation (peak, wk 4; early, wk 8 to 12; mid, wk 17 to 21; and late, wk 27 to 31). Treatments were duodenal infusions of 1) Met, 2) Lys, 3) Met plus Lys, and 4) casein; periods were 7 to 10 d. Quantities of DL-Met, L-Lys, and casein infused at the four stages of lactation were 12, 30, and 400; 12, 30, and 400; 10, 25, and 333; and 8, 20, and 266 g/d, respectively. Rations were composed of corn and grass-legume silages, corn meal, wheat middlings, soybean meal, and distillers dried grains with solubles. Intake of CP (percentage of NRC) and percentage of total CP from corn sources were (peak) 87, 56; (early) 90, 71; (mid) 98, 73; and (late) 114, 77. Using content and yield of milk protein as primary response criteria, Lys appeared to be first-limiting and Met second-limiting at peak lactation, their infusion together resulted in the same production of milk (40 kg/d) and milk protein (1135 g/d) as did casein. Lysine was first-limiting in early lactation, but whether Met was second-limiting was questionable. The two AA were colimiting in midlactation. There appeared to be no AA deficiencies in late lactation. Amounts of Lys and Met (percentage of total essential AA) in duodenal digesta during peak (12.4, 3.7), early (12.6, 3.5), and midlactation (14.9, 3.9) were not adequate for optimal AA utilization.

Amino acid limitation and flow to the duodenum at four stages of lactation. 2. Extent of lysine limitation.

Four multiparous Holstein cows with ruminal and duodenal cannulas were assigned to 4 x 4 Latin squares at peak (wk 4), early (wk 14 to 16), mid (wk 21 to 23), and late (wk 29 to 31) lactation to determine, in the presence of supplemental Met, the extent of Lys limitation and its required contribution to total essential AA in duodenal digesta. Treatments were duodenal infusions of 1) water alone or water with 2) 10 g/d of DL-Met plus 10 g/d of L-Lys, 3) 10 g/d of Met plus 20 g/d of Lys, and 4) 10 g/d of Met plus 30 g/d of Lys; quantities were reduced by 20% in late lactation. Rations were corn based (corn and grass-legume silages, corn meal, wheat middlings, soybean meal, and distillers dried grains with solubles) and most limiting in Lys and Met. Intakes of ruminally degraded and undegraded intake protein (percentage of NRC requirements) were (peak) 115, 97; (early) 112, 83; (mid) 113, 87; and (late) 127, 96. Contribution of Lys to passage of total essential AA to the duodenum without infusions were 13.2, 12.4, 13.8, and 14.8% at the four respective stages of lactation. Extent of Lys limitation determined from responses in content and yield of milk protein approximated 25, 20, and 10 g/d during peak, early, and midlactation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prepartum dietary energy on condition score, postpartum energy, nitrogen partitions, and lactation production responses.

Objectives were to examine the effects of feeding to alter body condition at calving on subsequent full lactation production performance and feed intake, on BW and periparturient blood traits, and on complete energy and N balances and ration digestibility during wk 6, 10, and 14 postpartum. Thirty pluriparous Holstein cows were assigned randomly to two energy intakes from wk 33 of previous lactation through the dry period to create either normal (7.2) or thin (5.8) mean body condition scores at calving (9 = fat, 1 = thin). The thin group was fed 0 kg hominy feed daily; the normal group was fed 2.7 kg daily to supplement forage DM available ad libitum during this period. When compared with the normal group, cows in the thin condition group exhibited less negative body fat balance (-206 vs. -507 g/d); similar milk yield, DM intake, N partitions, and nutrient digestibilities; and lower fat test (3.2 vs. 4.1%) during the balance measurements. Whole blood and serum traits were within normal physiological ranges. Full lactation measurements were similar between treatments except that milk fat percentage was lower and DM intake (as percentage of BW), was higher in the thin condition group. Although mean BW at calving was more (651 vs. 599 kg) for normal condition cows, condition scores and BW were not significantly different at 14 wk postpartum; BW curves indicated similar rates of recovery of weight thereafter. Cows considered underconditioned at parturition mobilized less body fat after calving, resulting in reduced milk fat concentration without significant effects on milk yield, protein, SNF, DM intake, or nutrient utilization.

Description and validation of an in situ autoperfusion method to determine nutrient absorption and metabolism in bovine small intestine.

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.

Varying protein content and nitrogen solubility for pluriparous, lactating Holstein cows: lactation performance and profitability.

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.