Nitrogen digestion and urea recycling in Hokkaido native horses fed hay-based diets.

Nitrogen (N) digestion and urea-N metabolism in Hokkaido native horses fed roughage-based diets containing different types and levels of protein sources were studied. Horses (173 ± 4.8 kg) fitted with an ileum cannula were fed four diets consisting of 100% timothy hay (TH), 88% TH and 12% soybean meal (SBM), 79% TH and 21% SBM, and 51% TH and 49% alfalfa hay at 2.2% of body weight. Dietary protein content varied from 5% to 15% of dry matter. Apparent N digestibilities in the pre-cecum and total tract for the TH diet were lower than those for other diets. However, the proportion of post-ileum N digestion to N intake was not affected by the diets. Urea-N production was linearly related to N intake, but gut urea-N entry was not affected by the diets. The proportion of gut urea-N entry to urea-N production tended to be higher for the TH diet (57%) than the two SBM diets (39%). Anabolic use of urea-N entering the gut was not affected by the diets (20-36% of gut urea-N entry). These results indicate that urea-N recycling provides additional N sources for microbial fermentation in the hindgut of Hokkaido native horses fed low-quality roughages.

Insulin-independent actions of glucagon-like peptide-1 in wethers.

Insulin-independent actions of glucagon-like peptide-1 (GLP-1) are not yet clear in ruminants. Four Suffolk mature wethers (60.0 ± 6.7 kg body weight (BW)) were intravenously infused with insulin (0.5 mU/kg BW/min; from 0 to 90 min) and GLP-1 (0.5 µg/kg BW/min; from 60 to 150 min) with both hormones co-administered from 60 to 90 min, in a repeated-measure design under euglycemic clamp for 150 min, to investigate whether GLP-1 has insulin-independent actions. Jugular blood samples were taken at 15-min intervals for plasma hormones and metabolites analysis. Compared to baseline concentrations (at 0 min), insulin infusion decreased (P < 0.05) plasma concentrations of glucagon, non-esterified fatty acids (NEFA), lactate, nonessential amino acids (NEAA), branched-chain amino acids (BCAA), total amino acids (TAA) and urea nitrogen (UN). Insulin plus GLP-1 infusion induced a greater increase (P < 0.05) in plasma concentrations of insulin and triglyceride (TG), but decreased (P < 0.05) glucagon, total cholesterol (T-Cho), NEAA and UN plasma concentrations. GLP-1 infusion increased (P < 0.05) NEFA, ß-hydroxybutyrate and TG, but decreased (P < 0.05) glucagon, T-Cho, NEAA, BCAA and UN plasma concentrations. In conclusion, GLP-1 exerts extrapancreatic roles in ruminants not only insulin-independent but probably, in contrast to non-ruminants, antagonistic to insulin effects.

Milk production, plasma metabolite profiles and mammary arterial-venous differences of milk precursors in early lactation cows milked at different frequencies by an automatic milking system.

The objective of this study was to clarify the effect of different milking frequencies under an automatic milking system (AMS) on milk yield, plasma metabolite profiles and mammary arterial-venous (A-V) differences of milk precursors by mammary tissues in early lactation cows. Twelve Holstein cows were divided into two and four times milking frequency treatments by AMS after calving to 50 days postpartum. Cows were given a partial mixed ration ad libitum and a concentrate diet at every milking. Dry matter intake increased similarly in both treatments with advancing postpartum days. Milk yield was greater (P < 0.001) by 25% with four times milking, but milk composition was not affected by milking frequency. Body weight change was also not affected by milking frequency. Arterial concentrations of glucose and glutamate were lower (P < 0.05) for four times milking frequency. However, arterial concentration of nonesterified fatty acids did not differ between treatments. Although mammary A-V differences of plasma concentration for most milk precursors did not differ between treatments, estimated plasma flow was higher (P < 0.05) for four times milking frequency. These results indicate that higher milking frequency may increase mammary uptake of milk precursors, whereas may not affect the extent of fat mobilization of early lactating cows from day 20 postpartum onward.

Use of a rigid-type polyethylene T-cannula, silicone tubing, and adhesion netting for surgical cannulation of ileum of the horse.

A rigid-type of polyethylene T-cannula was fitted into the anterior ileum of six horses in order to improve the cannulation techniques. A piece of polyethylene net was fastened onto the intestinal wall around the cannula to prevent dislodgment of the cannula by promoting a secure adhesion between the ileum and the abdominal wall. The cannula barrel sheathed with silicone tubing was exteriorized through a stab incision at the lateral ventral wall on the transverse line of the second lumber vertebra, and a flange was screwed onto the barrel. The feeding regime gradually increased concentrate without roughage prevented any colic signs. The use of these techniques succeeded in the ileal cannulation with no leakage of digesta.

Effects of dietary combination of corn and rice as whole crop silage and grain sources on carbohydrate digestion and nitrogen use in steers.

Four Holstein steers were used to evaluate the combination effects of whole crop corn (Cs) or rice (Rs) silage with steam-flaked corn (Cg) or rice (Rg) grain (four dietary treatments) on ruminal carbohydrate digestion, duodenal nitrogen (N) flow and plasma essential amino acid (EAA) concentration. The ruminal digestibility of starch and nonfiber carbohydrate (NFC) for Rs and Rg diets compared with Cs and Cg diets was greater, but that of neutral detergent fiber (aNDFom) was less. Because the ruminal disappearance of NFC plus aNDFom was similar across four dietary treatments, microbial N flow was not affected by the diets. There was an interaction of methionine (Met) flow by silage and grain sources: greatest for CsRg and least for RsRg diet, and blood plasma concentration of Met after feeding was lower for Rg than Cg diets. Postprandial reduction degree of plasma EAA varied with the diets and individual EAA. The Cs diets compared with the Rs diets tended to be greater in N retention because of greater digestible organic matter (OM) intake. These results suggest that silage source combined with corn or rice grain affects N use in steers through the digestible OM intake, and the kinds of limiting AA may differ among the combination of silage and grain sources.

Effects of intravenous ghrelin injection on plasma growth hormone, insulin and glucose concentrations in calves at weaning.

Ghrelin action, which stimulates growth hormone (GH) secretion, may alter during the weaning period in calves. Our objective was to compare the effects of intravenous ghrelin injection on plasma GH, insulin and glucose concentrations in calves around the weaning period. Four Holstein bull calves were fed whole milk and allowed free access to solid feeds, and weaned at 7 weeks of age. Measurements were performed at weeks 1, 2, 4, 6, 7, 9, 11 and 13, when calves were intravenously injected with ghrelin (1.0 µg/kg body weight (BW)) through a catheter, and jugular blood samples were obtained temporally relative to the injection time. Estimated digestible energy intake per metabolic BW transiently decreased at week 7 because of low solid intake immediately after weaning, and thereafter gradually increased. Plasma insulin and glucose concentrations were not affected by ghrelin injection at all ages. In contrast, plasma GH concentrations increased with ghrelin injection at all ages. The incremental area of GH at week 7 was greatest and significantly higher compared with weeks 2, 4, 6 and 9. This result suggests that nutrient insufficiency immediately after weaning enhances GH responsiveness to ghrelin.

Effects of high ambient temperature on urea-nitrogen recycling in lactating dairy cows.

Effects of exposure to hot environment on urea metabolism were studied in lactating Holstein cows. Four cows were fed ad libitum a total mixed ration and housed in a temperature-controlled chamber at constant moderate (18°C) or high (28°C) ambient temperatures in a cross-over design. Urea nitrogen (N) kinetics was measured by determining urea isotopomer in urine after single injection of [(15) N(2) ]urea into the jugular vein. Both dry matter intake and milk yield were decreased under high ambient temperature. Intakes of total N and digestible N were decreased under high ambient temperature but urinary urea-N excretion was increased. The ratio of urea-N production to digestible N was increased, whereas the proportion of gut urea-N entry to urea-N production tended to be decreased under high ambient temperature. Neither return to the ornithine cycle, anabolic use nor fecal excretion of urea-N recycled to the gut was affected by ambient temperature. Under high ambient temperature, renal clearance of plasma urea was not affected but the gut clearance was decreased. Increase of urea-N production and reduction of gut urea-N entry, in relative terms, were associated with increased urinary urea-N excretion of lactating dairy cows in higher thermal environments.

Differential localization of lingual antimicrobial peptide in the digestive tract mucosal epithelium of calves.

Immunolocalization of lingual antimicrobial peptide (LAP), a member of the ß-defensin family, in the digestive tract of calves was investigated to determine its distribution in the digestive tract of Holstein-Friesian calves. Various regions of the digestive tract were collected from slaughtered calves, and fixed in 10% formalin in PBS. Paraffin sections were stained with anti-LAP antibody, followed by visualization of immunoreactions products utilizing the avidin-biotin complex method. Expression of LAP mRNA was analyzed with reverse transcription-PCR. Immunoreactive LAP was localized in the stratum corneum of the stratified squamous epithelium of the tongue, esophagus, rumen, reticulum and omasum but not in their basal layer and lamina propria. In the gastric glands of the abomasum, only chief cells showed LAP positive reaction at the apical side of their cytoplasm. Lamina propria and Peyer's patch of the ileum had some leukocyte-like cells immunopositive for LAP. Weak immunoreaction of LAP was also detected in the mucosal epithelium of the intestinal gland of the cecum, colon and rectum. All regions of digestive tract showed LAP mRNA expression with PCR. These results indicate differential localization of LAP in the mucosal epithelium of digestive tracts in calves. The LAP expressed in stratum corneum of stratified squamous epithelium and chief cells of abomasum specifically may play role in the innate immune function in these tissues.

Effects of amino acids infused into the vein on ghrelin-induced GH, insulin and glucagon secretion in lactating cows.

To investigate the effects of amino acids on ghrelin-induced growth hormone (GH), insulin and glucagon secretion in lactating dairy cattle, six Holstein cows were randomly assigned to two infusion treatments in a cross-over design. Mixture solution of amino acids (AMI) or saline (CON) was continuously infused into the left side jugular vein via catheter for 4 h. At 2 h after the start of infusion, synthetic bovine ghrelin was single injected into the right side jugular vein through the catheter. Ghrelin injection immediately increased plasma GH, glucose and non-esterified fatty acids (P<0.05) with no difference between both treatments. Additionally, plasma insulin and glucagon concentrations were increased by ghrelin injection in both treatments. The peak value of plasma insulin concentration was greater in AMI compared with CON (P<0.05). Plasma glucagon concentration showed no difference in the peak value reached at 5 min between both treatments, and then the plasma levels in AMI compared with CON showed sustained higher values (P<0.05). After plasma glucose concentration reached the peak, the decline was greater in AMI compared with CON (P<0.05). These results showed that the increased plasma amino acids may enhance ghrelin action which in turn enhances insulin and glucagon secretions in lactating cows.

Effects of glucose and amino acids on ghrelin secretion in sheep.

Two experiments were conducted to elucidate the effects of post-ruminal administration of starch and casein (Exp. 1), plasma amino acids concentrations (Exp. 2), and plasma glucose and insulin concentrations (Exp. 2) on plasma ghrelin concentrations in sheep. In Exp. 1, plasma ghrelin concentrations were determined by four infusion treatments (water, cornstarch, casein and cornstarch plus casein) in four wethers. Abomasal infusion of casein increased plasma alpha-amino N (AAN) concentrations. Infusion of starch or casein alone did not affect plasma ghrelin concentrations, but starch plus casein infusion increased plasma levels of ghrelin, glucose and AAN. In Exp 2, we investigated the effects of saline or amino acids on ghrelin secretion in four wethers. Two hours after the initiation of saline or amino acid infusion into the jugular vein, glucose was also continuously infused to investigate the effects of blood glucose and insulin by hyper-glycemic clump on plasma ghrelin concentrations. Infusion of amino acids alone raised plasma levels of ghrelin, but the higher plasma glucose and insulin concentrations had no effect on plasma ghrelin concentrations. These results suggest that high plasma levels of amino acids can stimulate ghrelin secretion, but glucose and insulin do not affect ghrelin secretion in sheep.

The effect of dietary ratios of corn silage and alfalfa hay on carbohydrate digestion and retention time of feed particles in the gastrointestinal tract of steers.

Four Holstein steers fitted with duodenal cannula were used in a 4 x 4 Latin square design to investigate the effect of the combination of corn silage (CS) and alfalfa hay (AH) in different ratios on the ruminal and intestinal digestion of carbohydrates and feed particle passage rate. Steers were fed mixed diets containing both CS and AH in ratios of 80:20, 60:40, 40:60 and 20:80 on a dry matter basis at 95% of ad libitum feed intake. The increase of AH proportion in diets increased dry matter intake and ruminal digestion of dry matter, non-fiber carbohydrate, neutral and acid detergent fiber linearly. Ruminal digestibility of neutral detergent fiber showed a quadratic response, and total digestibility increased linearly with increasing AH proportion. Digestibility of acid detergent fiber in the rumen was not affected by the dietary treatments, but the total tract digestibility increased as the AH proportion increased. Mean retention time of feed particles in total compartment increased when the AH proportion increased from 20% to 60%, but decreased with further increase of the AH proportion. These results indicate that moderate combinations of CS and AH have an associative effect on ruminal fiber digestion, modifying particle movement in the rumen.