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The hypothesis was proposed that the carbohydrate in the first diet fed to turkey hatchlings upregulates the glucose transport system. Heavy and light body mass poults were observed to determine differences in glucose transport and carbohydrate digestion. Poults were weighed immediately posthatching. Heavy poults were at least +/-2 S.D. above the mean whereas light poults were at least +/-S.D. below the population mean (62.5 +/- 0.4). Each group was randomly assigned to one of two diets. One diet contained 50% carbohydrate and the remaining diet had 15% carbohydrate. Although the diets were isocaloric, differing carbohydrate (corn starch) and fat (cottonseed oil) content had significant effects on body masses within 3 days. Poults fed low carbohydrate weighed more than those on high carbohydrate perhaps because fat is a preferred energy substrate in the neonatal turkey. Greater carbohydrate in the diet increased glucose uptake and maltase activity compared to diets containing more fat. Heavier poults at hatching remained heavier at 3 days posthatching. No differences between body mass categories were noted in glucose uptake measurements. Thus, differences seen in growth rates may not be attributed to glucose transport in the jejunum. It is concluded that turkeys belong to the class of birds in which the poults respond to more carbohydrate in the diet by increasing plasma T(3) concentrations, upregulating the glucose transport system, and increasing enzymatic activity as with maltase.

Mice trisomic for the distal portion of MMU 16 (Ts65Dn) were examined for differences in jejunal function and plasma amino acids as compared to diploid controls. Eighteen control and 19 Ts65Dn mice were compared for whole-body and intestinal O2 consumption, jejunal glucose uptake, and plasma amino acid concentrations. Ts65Dn mice consumed less (P < 0.02) O2 per gram of fasted body weight. No significant differences were found in either active or passive glucose uptake. Oxygen consumption by jejunal tissue was not different between Ts65Dn and control mice. The apparent energetic efficiency of jejunal active glucose uptake (eta mol ATP expended/eta mol glucose uptake) was significantly higher (115.6 vs. 80.8; P < 0.05) in Ts65Dn mice. Histomorphometric analysis of jejunal mucosa showed that Ts65Dn mice had shorter villus height (P < 0.04) and decreased planar villus circumference (P = 0.05). No differences were found in total jejunal protein (microgram/g) or DNA (mg/g) concentrations. Significantly higher concentrations of plasma tyrosine, phenylalanine, valine, leucine, isoleucine, and citrulline (P < 0.05) were found in Ts65Dn mice. Lower plasma concentrations of hydroxyproline were detected in Ts65Dn mice (P < 0.05). These data suggest that Ts65Dn mice have anomalies in digestive function and amino acid metabolism as compared to normal, diploid controls.

Five-wk-old male mice from three lines were used to examine whether the apparent energetic efficiency of active jejunal glucose uptake in mouse jejunum is altered by genetic selection for different body composition. The mice lines were selected as follows: HE, high percentage of body fat with no change in body weight as a constraint; LF, low percentage of body fat; and RS, randomly bred control. Body weight was similar in all lines. Total jejunal O2 consumption and ouabain-sensitive O2 consumption were used to estimate the energy expenditure associated with glucose absorption and Na+/K(+)-ATPase activity. Tritiated 3-O-methyl-D-glucose was used to determine glucose uptake by mouse jejunum. Line LF, when compared with line HE, had lower body fat as indicated by epididymal fat pad weight (143 vs. 362 mg/mouse, P < 0.001). There were no significant differences in small intestinal weight, length and density (mg/cm) between LF and HE lines. Jejunal villus width was greater in line LF compared with line HE (115 vs. 92 microm, P < 0.002). Jejunal glucose transport and O2 consumption were not different between LF and HE lines. Ouabain-sensitive O2 consumption was not significantly different among the three lines. No differences were noted in the apparent energetic efficiency of active glucose uptake among lines.

Five-wk-old male mice from high growth (M16) and randomly bred control (ICR) lines, plus their reciprocal crosses, ICR x M16 and M16 x ICR, were used to investigate whether whole-body O2 consumption, jejunal respiration, jejunal glucose absorption and the apparent energetic efficiency of jejunal active glucose uptake in mice are altered by genetic selection for growth as well as by heterosis and maternal effects. Whole-body O2 consumption was measured in 12 mice from each line or cross. The mice were later killed for measurement of jejunal O2, using tissue respiration chambers and jejunal glucose transport determined by 3H-3-O-methylglucose accumulation. No heterosis or maternal effects were detected in jejunal glucose active transport and active glucose uptake. Selection for growth (M16 vs. ICR) increased daily gain (1.54 vs. 1.09 g, P < 0.001), small intestinal length and weight, but did not enhance jejunal glucose transport. The apparent energetic efficiency of jejunal active glucose uptake among lines was not different (54.0, 50.4, 51.6 and 47.1 nmol ATP expended/nmol glucose uptake for M16, ICR, M16 x ICR and ICR x M16, respectively, P > 0.63). Selection for growth in mice did not result in more energetically efficient jejunal glucose absorption.

In digesting and absorbing dietary nutrients, the gastrointestinal tract consumes approximately 20% of all incoming energy. A substantial proportion of this consumption is due to the rapid turnover of cellular protein, which permits abrupt changes in gut size to occur, matching capacity with delivery. If it is size of the alimentary tract that constrains nutrient uptake, greater than 20% allocation of ME intake above maintenance to the gut would improve the growth rate of a young animal but the efficiency of ME utilization for growth would deteriorate. Less than 15% allocation in birds seems injurious to both growth rate and efficiency of growth. Nutrient transport capacity of the intestine may be modulated independent of size; in the case of glucose, an up- or down-regulation of the number of brush-border glucose transporters matches absorptive capacity with delivery. The maximum uptake capacity of a small intestine for glucose at any moment in time is a function of its length, the flow rate of digesta, and the distributed-in-space kinetic parameters of transport (e.g., Vmax and Km). An example maximum uptake capacity for glucose in sheep is calculated at 2,112 g/d, assuming continuous digesta flow. Intermittency of flow reduces the uptake capacity to a functional level of 295 g/d, demonstrating a constraining influence of the periodicity of the migrating myoelectric complex. Growth regulation by stimulatory and inhibitory mitotic signals is presented as a candidate for an energy-independent determinant of the upper limit to functional maximum uptake capacity of the small intestine. Both size and functional capacity of the intestine must be considered in assessing the impact this tissue may have on the rest of the animal.

Terminal hydrolysis of oligosaccharides at the small intestinal brush border yields monomeric glucose, most of which is then absorbed by the transepithelial route. This involves carrier-mediated processes requiring specialized functional proteins situated in the brush border (SGLT1) and basolateral (GLUT2) membranes. Glucose translocation at the enterocyte apical membrane is an active, Na(+)-dependent and saturable process, whereas exit from enterocytes is by facilitated diffusion and is energy-independent. Specific adaptation of glucose active transport occurs in response to changes in the proportion of glucose in the diet. The regulatory signals responsible for transport induction are imprecisely defined, although numerous protein hormones and gut regulatory proteins are implicated. Epidermal growth factor and peptide YY invoke up-regulation of jejunal active glucose transport in vivo. Recently, peptide YY has been shown to stimulate active glucose transport in mice without altering oxygen consumption of jejunal tissue. Several other peptides whose presence in tissues of the small bowel imply that they exert control over epithelial nutrient transport are considered, and the relevance of these physiological manipulations, with various regulatory peptides and hormones, to animal agriculture are discussed.

The influence of slaframine (SF), a parasympathomimetic compound isolated from the fungus Rizoctonia leguminicola, on circulating metabolic hormone concentrations was investigated in goats. In Exp. 1, SF was administered i.v. at 0 (CONT), 50 (LSF), 100 (MSF), or 150 (HSF) microgram/kg.75 BW in four mature Spanish-cross does (average BW 36 +/- 7 kg) fitted with indwelling jugular vein catheters in a 4 x 4 Latin square design. Plasma glucose peaked (P < .06) at 120 min with LSF and at 180 min with HSF and was higher (P <.06) than the CONT at these times. Glucose exhibited a quadratic response (P < .03) to SF. Area under the response curve for glucose differed (P < .02) in HSF from CONT and MSF. Insulin peaked (P < .01) at 240 min with MSF and at 180 min with HSF. Plasma triiodothyronine was maintained at a higher level (P < .03) with HSF. Thyroxine peaked (P < .06) at 120 min with MSF and 300 min with HSF. Plasma NEFA and somatotropin concentrations were not affected (P > .10) by SF. In Exp. 2, four mature Spanish-cross wethers (average BW 27 +/- 2 kg) fitted with jugular vein catheters were administered SF (0 and 114 micrograms/kg.75 BW) and 4-diphenylacetoxy-N-methylpiperidine methiodide (4DAMP; 0 and 258 micrograms/kg.75 BW), a M3-muscarinic receptor antagonist, i.v. in a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. With SF, glucose peaked (P < .06) at 60 min and insulin peaked (P < .05) at 180 min. Plasma triiodothyronine levels were maintained (P < .05) with SF but declined with other treatments. Plasma NEFA and thyroxine concentrations remained unchanged regardless of treatment. Slaframine administration induced hyperglycemia and hyperinsulinemia in goats; however, these changes were blocked by preadministration of isomolar quantities of the M3-muscarinic receptor antagonist, 4DAMP.

The effect of duodenal slaframine (SF) infusion on site and extent of digestion was determined using four steers equipped with ruminal, duodenal, and ileal cannulas in a 4 x 4 Latin square. A 77% dry-rolled corn diet was provided in 12 equal portions daily at a DMI of 2.26% BW. Slaframine in a .9% saline excipient was infused into the duodenum every 12 h with total daily dose of 0, 30, 60, or 90 micrograms /kg of BW. Slaframine infusion had no effect on ruminal pH, ruminal NH3 N, or solids and liquids passage rate. Slaframine increased (linear, P < .10) total tract OM and starch disappearance and digestibility and tended to increase (linear, P = .14) total tract N digestibility. Ruminal starch disappearance tended to be decreased (quadratic, P = .16) by SF. Small intestinal OM digestibility was increased (linear, P < .10) but starch digestibility in the small intestine was not affected by SF. Increased total tract starch digestibility was caused by increased (quadratic, P < .10) starch fermentation in the large intestine. Ruminal feed N digestibility decreased at the intermediate doses of SF (quadratic, P < .10). Total N digestibility in the small intestine tended to be increased (cubic, P = .13) with 30 and 90 micrograms of SF/kg of BW. Decreased ruminal feed N digestion was compensated for by increased (quadratic, P < .10) small intestinal feed N disappearance for steers treated with intermediate doses of SF. The potential of SF to increase starch digestion in the rumen and small intestine seems to be limited.

The history of "slobbers syndrome," a mycotoxicosis associated with Rhizoctonia leguminicola infestation of pastures and stored forages, is discussed. The chemistry and physiological effects of the two known biologically active alkaloids of R. leguminicola, slaframine and swainsonine, are described. Slaframine administration is generally associated with increased exocrine function, especially salivation. Ingestion of swainsonine may be linked to serious and potentially lethal central nervous system defects similar to that described for locoism. However, the singular effects of these alkaloids do not completely account for the total clinical picture noted in the field during the occurrence of slobbers syndrome. It is possible that this phenomenon is the result of an interaction between both known and unidentified biologically active metabolites of R. leguminicola.

Experiments were conducted to determine 1) the effect of injecting slaframine (SF) on salivary output in growing beef steers and 2) whether increased salivary output after SF injection would inhibit the decrease in ruminal pH that occurs after experimentally induced subacute and acute ruminal acidosis. In Exp. 1 and 2, we measured ruminal pH and salivary output in ruminally and esophageally cannulated beef steers fed an 88% concentrate diet. Injections of 66 or 100 micrograms of SF/kg BW increased salivary flow approximately 50% compared with controls. Those doses were tested in subacute and acute acidosis models using ruminally cannulated beef steers in Exp. 3 and 4, respectively. In these experiments, salivation was assessed indirectly using a visual scoring system. In the subacute acidosis model, SF reduced (P < .10) the decrease in ruminal pH (1.1, .7, and .6 pH units for control, 66, and 100 micrograms of SF/kg BW doses, respectively), and excessive salivation was observed in all SF-injected steers. In the acute acidosis model, there were no differences (P > .10) in ruminal pH at 12 h after injection between control and SF-treated steers. Mean ruminal lactate concentrations for all treatment groups were between 87 and 112 mM. Although treatment with 66 micrograms of SF/kg BW reduced (P < .10) ruminal lactate concentrations, all ruminal lactate concentrations were indicative of acute acidosis. These results indicate that SF will reduce the decrease in ruminal pH associated with subacute acidosis in growing beef steers, but SF does not attenuate acute ruminal acidosis.

Small intestinal glucose absorption and gastrointestinal morphology were compared in adult bovine somatotropin transgenic (MT-bGH) and control mice. The MT-bGH mice were 57% heavier than controls, although both groups consumed comparable amounts of food during the 5 d before transport measurements were made. Stomach, cecum and colon were 98, 53, and 81% heavier (P < 0.001), and small intestinal tract 52% heavier and 27% longer in MT-bGH than in control mice (P < 0.001). As a proportion of live weight, MT-bGH mice tended to have a shorter small intestine than controls (P < 0.07), whereas there was no difference for either small or large bowel relative weights. Villus dimensions, crypt depth and thickness of external muscle layers in the jejunum were not significantly different in control and MT-bGH mice. Active glucose transport rate per milligram of jejunum was 24% less than in control mice (P < 0.05). Jejunal active glucose transport rate per gram of live weight in MT-bGH mice was approximately half that of control mice. The larger small intestinal mass of MT-bGH mice compensated for the reduced rate of glucose transport per unit weight of intestine such that there was no significant difference in total small intestinal tract glucose transport between control and MT-bGH mice. These results suggest that there are substantial differences in nutrient absorptive efficiency between intestinal tract from MT-bGH and control mice.

Eight Holstein cows were assigned following calving to two groups, balanced for parity, using a continuous completely randomized block design. Cows were fed a diet with 13.5% CP and 22.4% ADF from 35 to 55 DIM and then 13.8% CP and 15% ADF from 56 to 92 DIM. Alfalfa grass hay was the forage source, and concentrate mixtures contained primarily corn and soybean meal. Cows were given daily intraperitoneal infusions of a solution of L-Leu (46.1 g, 84.2 mM), L-Ile (31.4 g, 57.3 mM), L-Val (38.3 g, 78.2 mM), and L-Arg (25.0 g, 34.4 mM) or physiological saline following the a.m. milking from 42 through 84 DIM. Infusion of AA significantly increased plasma concentrations of Leu, Ile, Val, and Arg. Effects of AA infusion occurred during the low fiber period. Cows receiving AA maintained daily milk fat yield, increased p.m. milk fat yield, decreased less in p.m. milk fat percentage, and increased daily and p.m. yields of C16 fatty acids in milk. During the posttreatment period, cows previously receiving AA declined in daily milk fat yield, milk fat percentage, and total daily C4 to C16 milk fatty acid yield. Results suggest that the infused AA may have increased de novo synthesis of C16 milk fatty acids.

The effects of epidermal growth factor on intestinal glucose transport were examined in mice. Glucose transport measurements were performed using an in vitro assay system that estimated the rate of accumulation of [3H]3-O-methyl-D-glucose. In Experiment 1, two-mo-old male and female mice were subcutaneously injected once daily with 0, 150 or 300 micrograms epidermal growth factor/kg body weight for 3 d. Jejunal glucose active transport was increased in a dose-dependent manner. There were no gender-related differences in intestinal glucose transport or the response to exogenous epidermal growth factor. In Experiment 2, 2-, 10- and 18-mo-old mice were administered 0 or 300 micrograms epidermal growth factor/kg body weight using a treatment similar to that used in Experiment 1. Active intestinal glucose transport was 30% greater in response to epidermal growth factor in each of the three age groups. Ouabain-sensitive and -insensitive jejunal oxygen consumption was increased in response to epidermal growth factor such that total jejunal respiration was stimulated 15 to 31%. The epidermal growth factor related percentage increase in glucose absorption was similar to the percentage increase in oxygen consumption such that the apparent energetic efficiency of glucose transport was unaffected. In both experiments, the active component of glucose transport was increased by epidermal growth factor while passive transport was not affected. Jejunal morphology and mucosal DNA and protein concentration were not altered by epidermal growth factor treatment. Epidermal growth factor-induced increases in intestinal absorption was not attributable to mucosal hyperplasia.

Three Holstein steers (345 +/- 22 kg) surgically fitted with a pancreatic cannula were used in two 3 x 3 Latin square design experiments to examine the effects of slaframine (SF), a muscarinic agonist, or 4-diphenylacetoxy-N-methylpiperidine methiodide (4DAMP), an M3 muscarinic glandular receptor antagonist, on pancreatic exocrine secretion. Pancreatic exocrine secretion was collected for 8 h postdosing at 30-min intervals beginning 1 h postfeeding. In experiment 1, steers were dosed with 0, 25, or 50 micrograms.kg-1 body weight (BW) of SF. Secretion of pancreatic juice and the pH of the secreted juice increased linearly (p < 0.05) with SF; however, secretion rate showed a time by treatment interaction (p < 0.05), as treatments converged 7 h postdosing. Trypsin secretion tended (p < 0.10) to show a quadratic response to SF administration, with the 25 micrograms SF.kg-1 BW dose having the lowest value. In experiment 2, steers received 50 micrograms.kg-1 BW of SF (positive control), 113 micrograms.kg-1 BW of 4DAMP (isosmolar with SF), or both. SF caused a greater pancreatic fluid secretion (p < 0.10) than 4DAMP, with SF plus 4DAMP intermediate. A time by treatment interaction (p < 0.04) was found, since treatments converged 8 h postdosing. Trypsin secretion was higher (p < 0.05) for SF than the other treatments. Chymotrypsin, alpha-amylase, and protein secretion were not affected. SF and 4DAMP alter pancreatic fluid secretion in the steer but have minimal effects on enzyme secretions.

Discussed herein are the constraints of nutrient delivery from the gastrointestinal tract that are placed on postabsorptive synthetic processes in highly selected strains of domestic livestock or livestock treated with growth promotants exogenously or via transgenic manipulation. Emphasis is placed on the discussion of recent advances in the knowledge of the regulation and manipulation of digestion and the absorption by the intestinal epithelium. Slaframine, a muscarinic exocrine secretagogue with a high affinity for the gastrointestinal tract, and epidermal growth factor may have practical potential for the manipulation of digestion and absorption, respectively. Special consideration is given to energetic considerations that must accompany any manipulation of gastrointestinal function. Down-regulation and up-regulation of mechanisms must be equally considered as this area is explored further.

Sixteen mature, ruminally cannulated wethers (average BW = 41 +/- 1 kg) were fed a low-quality hay diet with or without a cottonseed meal (CSM) supplement and the parasympathomimetic agonist slaframine (SF). Treatments were basal diet (Mitchell grass hay, 4.8% CP, 46.8% ADF) available on an ad libitum basis, basal diet plus SF (8 micrograms/kg BW, 2 x daily i.m. injection), basal diet plus CSM (41.0% CP; 100 g/d), or basal diet plus SF and CSM. Treatments were arranged as a 2 x 2 factorial within a replicated 4 x 4 Latin square with 20-d periods followed by a 10-d adjustment during which only the basal diet was fed. All measurements were performed within the final 10 d of each period. Slaframine increased salivary flow by 10 to 35% (P < .07), ruminal fluid dilution rate by 8 to 11% (P < .10), and pH by 3 to 4% (P < .001). A twofold increase (P < .05) in ruminal cellulolytic bacteria numbers occurred in SF-treated wethers. Despite these SF-induced changes in the ruminal environment, whole-tract apparent nutrient digestibility, N and mineral balance, and ruminal VFA concentrations were not changed. Cottonseed meal increased forage intake by 34 to 54% (P < .001) and DM digestibility by 30% (P < .001). Cottonseed meal supplementation of a Mitchell grass hay diet improved nutritional status and attenuated live weight loss.

An organ explant culture system for the intact chick pancreatic splenic lobe (SL) was characterized for exocrine function. Organ cultures were prepared using the pancreatic splenic lobe from 9- and 15-day-old male broiler chicks (Arbor Acres x Arbor Acres) to characterize amylase release as well as tissue integrity during 2, 4, 8, and 12 h of incubation. Light microscopy studies indicated necrosis of the exocrine pancreatic acini after 4 h of incubation. Changes in islets of Langerhans were noted 4 h after incubation, but islet structural integrity remained intact for up to 12 h of incubation. Lactate dehydrogenase (LD) levels measured in the culture medium did not increase significantly from 2 to 4 h of incubation. After 4 h of incubation, total LD levels increased (P < .05) for the 9-day-old SL cultures, and LD levels increased (P < .01) per unit weight of SL for the 15-day-old cultures. Medium amylase activity did not increase after 2 h of incubation. Large increases occurred for total amylase activity and amylase activity per unit weight of SL between 4 and 12 h of incubation for both 9- and 15-day-old cultures. Histological examination as well as increases in LD and amylase activities for total and per unit weight of SL in the incubation medium suggest that the viability of the 9- and 15-day-old SL organ incubation system decreases after 4 h.

Mechanisms regulating ruminant pancreatic exocrine function differ in some respects from those in nonruminants. This may affect the post-ruminal digestion of certain dietary nutrients such as starch. Ruminants do not exhibit clearly defined cephalic and gastric phases of pancreatic regulation, a likely consequence of the continuous nature of digesta flow from the rumen. Local neural reflexes and secretin-mediated exocrine responses may be more important than stimulation by cholecystokinin. Additionally, the ruminant pancreas may be stimulated by short-chain fatty acids produced in the rumen. A "ruminal phase" of pancreatic exocrine regulation has been proposed. The failure of cattle to digest efficiently starch in the small intestine may result from an asynchrony between delivery of starch to the intestines and pancreatic amylase release.

Twenty multiparous and 12 primiparous Holstein cows were assigned at calving to one of three grass hay-based diets containing either 14, 18, or 22% CP or an alfalfa hay-based diet containing 22% CP to examine the effect of protein level and forage source on milk yield and composition. The diets contained 23% ADF during wk 1 to 4 postpartum, which was lowered to 11% for wk 5 to 12 postpartum. Cows fed the 18 and 22% CP grass-based diets produced higher yields of milk, 4% FCM, fat, protein, and SNF than those fed the 14% CP diet during the high fiber period. In addition, cows fed the 22% CP grass-based diet had higher milk fat tests than those fed the 14% CP diet during the high fiber period, due primarily to an increase in short-chain fatty acid synthesis. Milk fat depression was more severe when cows were changed to low fiber diets while fed the 22% CP alfalfa-based diet than when fed the 22% CP grass-based diet. Depression in milk fat content was 15.0, 17.0, 15.6, and 27.0% for 14, 18, and 22% CP grass-based and 22% CP alfalfa-based diets, respectively. Cows receiving the 18 and 22% CP grass-based diets exhibited higher blood NEFA during the high fiber feeding period than those fed the 14% CP diet. After fiber was lowered, changes in rumen acetate:propionate ratios were unaffected by treatment. Lowering fiber level resulted in an increased milk CP percentage regardless of treatment. Grass hay appeared to be more effective than alfalfa hay in preventing depression in milk fat test upon the change to a low fiber diet.

Exocrine secretions in the digestive tract of domestic livestock are controlled by a combination of neural and endocrine inputs. The parasympathetic domain of the autonomic nervous system is responsible for efferent signals that regulate most exocrine secretory processes. Exocrine tissues possess cholinergic muscarinic receptor subtypes that are different from those found in brain, heart and muscle tissues. Cholinergic stimulation of specific muscarinic receptor subtypes has enhanced secretions of the salivary glands and pancreas. These changes in output of exocrine glands can alter digestive function that may benefit production of cattle and swine.

Four calves (avg wt 161 kg) were surgically fitted with indwelling catheters in the femoral artery and femoral, portal, hepatic and mesenteric veins to study the effects of subclinical ammonia toxicity on portal-drained viscera (PDV) and hepatic (HEP) net flux of key metabolites and pancreatic hormones. Hyperammonemia was induced via administration of ammonium chloride (NH4Cl; 12 mumol.kg BW-1.min-1) via the femoral vein catheter for 240 min; infusions were preceded (PRE) and followed (POST) by 60- and 180-min control periods, respectively. Blood samples were obtained from the arterial catheters, and portal and hepatic vein catheters. Net flux rates were calculated by multiplying venoarterial differences by blood flow. Arterial plasma ammonia N peaked (P less than .01) at 327 micrograms/dl; hepatic ammonia extraction increased (P less than .01) from 10 to 23% during NH4Cl infusion. Arterial plasma glucose concentrations increased (P less than .05) during NH4Cl infusion (90.5 vs 82.6 mg/dl) concomitant with trends toward a reduction in net HEP glucose output. Portal-drained visceral release of insulin did not increase (P greater than .10) during NH4Cl infusion despite the steady rise in circulating glucose concentration; however, cessation of NH4Cl infusion resulted in a 109% increase (P less than .05) in PDV insulin release at +60 min POST. Plasma L-lactate, nonesterified fatty acids, urea N and glucagon concentrations and net fluxes were variable throughout the experiment. Results tend to indicate that hyperammonemia reduced hepatic glucose output and glucose-mediated pancreatic insulin release.

Twenty-eight Holstein cows were in a reversal trial to determine effects of adding 34 g/day of methionine hydroxy analog to a low fiber ration. Cows were subjected to this feeding treatment sequence after parturition: days 1 through 28, normal fiber ration; days 29 through 56, low fiber ration; days 57 through 77, low fiber ration with or without 34 g/day of methionine hydroxy analog; days 78 through 98, low fiber ration; days 99 through 119, low fiber ration with or without 34 g/day of methionine hydroxy analog (days 57 through 77 treatments reversed). Milk, rumen fluid, and blood were collected at regular intervals during each period. Overall, supplementation with methionine hydroxy analog increased only milk fat 6%. After milk fat percentage was depressed by low fiber diet, supplementation with methionine hydroxy analog increased milk fat percentage only for those cows that initially had less than 20% decrease of milk fat percentage. This enhanced milk fat percentage was accompanied by increase of ratio of ruminal acetate to propionate in animals with less than 10% depression. Supplementation with methionine hydroxy analog had no effect on blood glucose, insulin, or acetate concentrations and did not affect uptake of acetate by the mammary gland. Initial milk fat production affects the ability of methionine hydroxy analog supplementation to enhance milk fat percentage of dairy cattle fed low fiber diets.

Thirty lactating Holstein cows were in two groups in a study of effects of vitamin B12 injections on milk fat synthesis. All cows were fed a normal fiber diet for the first 28 days after calving and then adjusted gradually to a low fiber diet over the next 28 days. After adjustment to the low fiber diet, in a single reversal trail, cows received either 150 mg of vitamin B12 in the form of hydroxocobalamin intramuscularly every 7 days for 21 days or no treatment for 21 days. Daily milk yield (kg), percent milk fat, and milk fat yield (g) for the normal fiber, low fiber adjustment, low fiber control, and low fiber plus vitamin B12 treatments were 29.6, 3.59, 1192; 31.5, 2.85, 840; 28.0, 2.58, 715; and 28.8, 2.65, 760. Injections of vitamin B12 did not correct the milk fat depression associated with the low fiber diets. In addition, there was no consistent relationship between blood B12 and milk fat production. Milk fat production was highly correlated with molar percent acetate in the rumen .63 and with blood acetate concentration .74.

Male mice selected for rapid 3 to 6 wk postweaning gain (M16) and unselected controls (ICR) were ad libitum fed a stock diet containing 0, 50 or 200 ppm cimaterol, a beta-agonist, from 4 to 7 or 4 to 10 wk of age. Mortality rate was higher in M16 than in ICR mice fed cimaterol (12.5 vs 1.3%; P less than .01). No mortalities occurred in either line fed the control diet. Line M16 exceeded (P less than .01) ICR in growth rate, feed intake, feed efficiency and lean index. Line X cimaterol level interactions (P less than .01) were found for the first three of these traits, although cimaterol level did not change line ranking. Epididymal fat as a percentage of empty body weight decreased at a faster rate in M16 than in ICR as cimaterol level increased. At 0 and 50 ppm, M16 exceeded ICR (P less than .05), but at 200 ppm there was no line difference (P greater than .05). Line M16 exceeded (P less than .05) ICR in blood glucose (5%), nonesterified fatty acids (4%) and lactate at 7 wk (9%), but lactate was higher in ICR at 10 wk (13%). Lines were not different in blood urea-N. Compared to zero cimaterol level, at 50 and 220 ppm glucose decreased (14% and 23%; P less than .05), nonesterified fatty acids decreased (3% and 29%; P less than .05), lactate increased (9% and 11%; P less than .05) and blood urea-N increased (3% and 16%; P less than .05). There were no line X cimaterol level interactions for blood metabolites. Differences in mortality rate, growth, feed consumption, feed efficiency and epididymal fat pad percentage between the high-growth and control lines in response to cimaterol may reflect genetic differences in mechanisms of metabolic regulation.

Twenty-four multiparous and 15 primiparous Holstein cows were fed a total mixed corn silage diet with one of three dietary treatments: 14% crude protein, 22% crude protein (all preformed), or 22% crude protein (preformed plus nonprotein N). Eight multiparous and 5 primiparous cows were randomly assigned to each treatment at calving. The diet contained 23% ADF during wk 1 to 4 postpartum and was lowered to 11% ADF for wk 5 to 12 postpartum. Treatment had no effect on the magnitude of depression in milk fat percentage or milk fat yield in multiparous cows. After fiber was lowered, changes in rumen acetate to propionate ratio, blood glucose, free fatty acids, and insulin were not influenced by treatment. Depression in milk fat percentage for primiparous cows was 19.7, 9.2, and 14.9% for low protein, high protein, and high protein with nonprotein N, respectively. When changed from high fiber to low fiber, the primiparous cows increased milk fat yield 9% for high preformed protein treatment but decreased fat yield for other treatments. Depression in acetate to propionate ratio and increase in blood glucose was least for the high preformed protein group.

The effect of the antibiotic, avoparcin, on ruminal propionate production and amino acid degradation was investigated by using four rumen fistulated wethers. Wethers were fed each of four diets during 28-day periods in a 4 X 4 Latin square design. Diets were high fiber (HF), high fiber plus 50 ppm avoparcin (HF-AVO), low fiber (LF) and low fiber plus 50 ppm avoparcin (LF-AVO). Total digestible energy intake (1.25 X maintenance) and crude protein intake for each animal were similar for all diets. Propionate production was determined each period from all animals by using a single injection of [1-14C]propionate and polyethylene glycol. Avoparcin decreased total volatile fatty acid concentration, increased ruminal pH and molar proportions of propionate on both HF and LF diets. Daily propionate production and pool turnover rate increased in sheep fed LF-AVO. Similar changes were noted in HF-AVO animals, although they were not statistically significant. Avoparcin decreased ruminal ammonia (50 vs. 45 mg/100 ml) and increased alpha amino nitrogen (8.6 vs. 14.3 mM) in LF-fed sheep. In vitro studies demonstrated a decreased degradation of crystalline amino acids by mixed populations of rumen microorganisms from sheep receiving LF diets containing avoparcin. Avoparcin appears to modify rumen fermentation by increasing propionate production and inhibiting protein or amino acid degradation.

Slaframine (SF), a parasympathomimetic salivary stimulant, was administered i.m. (10, 15 or 20 micrograms SF/kg BW) to ruminally and abomasally fistulated steers at 12-h intervals for 18-d periods in a latin square-designed experiment. Steers were fed semicontinuously (12 times daily) a 40:60 roughage:concentrate diet at twice their net energy requirement for maintenance. Ruminal digestion coefficients for DM, ADF and starch were 10 to 16% lower and linearly related in an inverse manner to the level of SF administered (P less than .05). Postruminal digestion of DM, ADF and starch increased as much as 46.7, 9.5 and 44.0%, respectively, in a fashion linearly related (P less than .05) to the level of SF administered. Total tract digestion of DM and ADF were not affected by SF; however, total tract starch digestion was increased as much as 5% and was related linearly (P less than .05) to SF treatment. With SF administration, as much as 13% more bacterial protein exited the rumen, resulting in a 16.5% linear improvement (P less than .1) in the efficiency of ruminal bacterial protein production per 100 g of OM fermented. Ruminal concentrations of VFA, ammonia and pH were not affected by SF. These results demonstrate a positive relationship between salivation and ruminal bacterial protein synthesis and suggest that feed utilization by ruminants may be improved by pharmacological stimulation of salivary secretions.

Three experiments with ruminally fistulated cattle fed 12 times daily were conducted to study the role of saliva secretion in ruminal water balance when intake, diet, and feeding pattern were altered. Water balance data were determined from continuously infused Co-EDTA and pulse-dosed Cr-EDTA with saliva flow estimated by difference between water intake and ruminal outflow. Any net transruminal water flux would be included in the estimate of salivary flow. When the concentration of bluestem hay in the diet was increased from 50 to 90%, ruminal fluid volume, saliva secretion, water intake, dilution rate, and total ruminal outflow increased. At equal intake, the higher forage diet increased ruminal liquid volume, outflow, and saliva secretion but had no effect on dilution rate. Intake, but not forage concentration, affected ruminal pH when 50 and 90% hay diets were fed. Increasing feeding frequency of forage in a 65% bluestem hay diet from 4 to 12 times daily (the grain portion was fed 12 times daily) increased dilution and ruminal outflow; however, the latter was only significant with data from Cr-EDTA. Ruminal volatile fatty acids were not altered by feeding frequency of forage. Nycterohemeral patterns were seen in water intake, ruminal dilution rate, outflow, and salivary flow in both studies. Slaframine increased saliva flow by 29% and was accompanied by increased ruminal liquid volume, dilution rate, and outflow.

Effect of purified slaframine (SF; 1-acetoxy-6-aminooctahydroindolizine), a parasympathomimetic secretagogue isolated from Rhizoctonia leguminicola, on ruminal motility was investigated in cattle and sheep. In trial 1, four ruminal cannulated wethers, fed a pelleted concentrate and hay diet, were injected intramuscularly with 0, 12, 24 and 48 micrograms SF/kg body weight (BW) in a 4 X 4 Latin-square design. Ruminal motility was recorded 1 h before and 1 to 2 h and 3 to 4 h after SF administration by measuring pressure changes exerted upon a fluid-filled, open-tipped catheter inserted into the dorsal sac of the rumen. The frequencies of both primary and secondary ruminal contractions were decreased as much as 20 to 78% with SF (P less than .05) depending upon the dosage level and time after administration. In trial 2, three ruminal-cannulated steers fed a concentrated diet were injected intramuscularly with 0, 12 and 24 micrograms SF/kg BW in a 3 X 3 Latin-square design. A water-filled balloon inserted into the cranial sac of the rumen was used to measure ruminal pressure changes 1 h before and 1 to 2 h, 3 to 4 h and 7 to 8 after SE administration. Frequency of primary and secondary ruminal contractions decreased with SF as much as 27 to 64% depending on the dosage level and time after administration. The frequency of secondary contractions increased 28% (P less than .05) as compared with control during the 7 to 8 h after administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Slaframine (SF), 1-acetoxy-6-aminooctahydroindolizine a parasympathomimetic with a high affinity for the gastrointestinal tract, was administered by oral intubation daily to 240 broiler chicks at either 0, 8.9, or 17.8 micrograms/kg body weight.75 (BW.75) in saline for 21 days. Throughout the experimental period weight, feed intake, and fecal output were measured. On Day 21 birds were killed, eviscerated, and wet organ weights were obtained. Pancreas and small intestine digesta were homogenized with saline and frozen for analyses of trypsin, chymotrypsin, amylase, and lipase activity as well as total protein. Weight, feed intake and utilization, pancreatic weight, liver weight, and small intestine digesta weight were not affected by SF treatment. Protein content of the digesta decreased 16.6% with the 17.8 micrograms SF/kg BW.75 treatment. Digesta lipase activity was 13.3% (P greater than .05) and specific activity 24% less (P less than or equal to .02) in 17.8 micrograms/kg BW.75 treated birds in comparison with those of controls, and activities decreased in a linear fashion across treatment levels (P less than or equal to .04). Digesta trypsin-specific activity decreased linearly with SF treatment (P less than or equal to .05), averaging 5.5 to 16.9% lower than control treated birds. Pancreatic chymotrypsin-specific activity was not significantly different among treatments. These results suggest that relatively small dosages of SF may affect digestive function of broiler chicks.

The possible association between low-fat milk syndrome and methylmalonic acid accumulation in blood was investigated. Blood was sampled from the internal iliac artery of nine lactating dairy cows fed ad libitum roughage plus grain or high grain, restricted roughage diets. Daily milk fat percent and milk fat production were decreased 44% and 47% on the high grain, restricted roughage diet. No differences in blood methylmalonate concentrations could be detected in the cows fed the two diets. The effect of methylmalonate and its metabolic precursor, propionate, on mammary rates of fatty acid synthesis was determined with bovine mammary tissue slices. Neither of these metabolites affected acetate incorporation into fatty acids. Methylmalonate and propionate were incorporated into fatty acids at extremely low rates. Low-fat milk syndrome is not caused by accumulation of methylmalonic acid.

Growing steers were used in a replicated 3 X 3 Latin square to study the influence of ionophores on mineral metabolism and ruminal urease activity. Treatments consisted of: 1) basal high energy diet; 2) basal plus 33 ppm lasalocid and 3) basal plus 33 ppm monensin. Each period was 33 days and apparent absorption and retention of macrominerals were measured during the last 5 days of each period. Mineral intake during the collection period was not affected by treatment. Both ionophores increased apparent absorption of sodium, magnesium and phosphorus. Retention of magnesium and phosphorus were higher for steers receiving either lasalocid or monensin. Potassium and calcium absorption were not significantly affected by treatment. Serum concentrations of macrominerals were similar for all treatments. Zinc and copper concentrations in serum were higher in animals fed monensin or lasalocid. Steers fed either ionophore had lower concentrations of soluble potassium and calcium in rumen fluid. Both ionophores also decreased ruminal osmolality. Bacterial urease, a nickel-dependent enzyme, was decreased by 28 and 66% in animals that received lasalocid and monensin, respectively. These findings indicate that lasalocid and monensin affect metabolism of certain minerals in ruminants.

The ability of slaframine (SF), a parasympathomimetic, to alter blood growth hormone (GH) and glucose concentrations in broiler chicks was investigated. Eighty male broiler chicks (average weight 225 g) were divided into 10 groups and dosed with either saline (control) or 1 mg SF/kg of body weight by oral intubation. Plasma samples were obtained from separate groups of chicks at 1, 2, 4, 8, and 12 hr after SF administration and analyzed for growth hormone and glucose. One hour after SF administration, glucose increased (P less than .05) 21.4% compared with controls. Growth hormone increased (P less than .05) 449 to 948% from 8 to 12 hr after SF administration. Administration of SF at 1 mg/kg of body weight was associated with increased plasma GH.

The effects of subclinical NH3 toxicity on circulating and regulatory hormone concentrations were investigated in seven Hereford steers. Ammonium chloride (NH4Cl) was infused via a right jugular vein catheter at a rate of 12 mumol NH4Cl.kg BW-1.min-1 for 240 min. This was preceded (PRE) and followed (POST) by saline infusions of 120 and 180 min, respectively. Blood samples were taken at 20-min intervals via a left jugular vein catheter. Metabolite and hormone concentrations during NH4Cl and POST periods were compared to PRE values using the Student's t-test procedure. Plasma NH3 was elevated rapidly (P less than .001) and peaked at 503 micrograms/dl 220 min into NH4Cl infusion. Plasma urea-N and glucose increased (P less than .001) 39 and 12%, respectively, during NH4Cl infusion and remained elevated 180 min POST. Whole blood L-lactate concentrations peaked (P less than .05) at 18% above PRE between 160 and 240 min into the NH4Cl infusion and gradually returned to PRE values, whereas pyruvate levels were not altered (P greater than .10). Plasma nonesterified fatty acids peaked (P less than .001) at 94% above PRE levels 40 min into NH4Cl infusion, thereafter declining to PRE concentrations. Whole blood acetoacetate and beta-hydroxybutyrate concentrations were not altered (P greater than .10) by NH4Cl administration. Plasma insulin concentration decreased (P less than .05) 26 to 46% during NH4Cl infusion and increased (P less than .05) 89 to 122% during POST. Plasma glucagon levels were not altered by NH4Cl infusion, so molar insulin:glucagon ratio changes resembled those of insulin. Plasma epinephrine, norepinephrine and dopamine did not vary (P greater than .10) with treatment. These results support the hypothesis that the hyperglycemia observed during hyperammonemia may result from an under-utilization of glucose by insulin-sensitive tissues.

Two trials were initiated to determine if slaframine (SF) can be used to alter fluid digesta flow and fermentation patterns in the rumen. In trial 1, a preliminary experiment, four Dorset X Barbados Black-belly ruminal-cannulated wethers (avg weight 41.6 8.7 kg) given ad libitum access to a pelleted concentrate/hay diet were injected intramuscularly with 0, 12, 24 or 48 micrograms SF/kg body weight (BW) in a 4 X 4 Latin-square design. Ruminal fluid dilution rate was determined using a single intraruminal infusion of polyethylene glycol (7 g), followed by seven hourly ruminal fluid samples. The administration of 48 micrograms SF/kg BW increased (P less than .10) ruminal volume and outflow by 27 and 25%, respectively, compared with controls. In trial 2, two Hereford and two Angus ruminal cannulated steers (avg weight 568 +/- 93 kg) were injected with 0, 6, 12 or 24 micrograms SF/kg BW at 8-h intervals over a 24-h period in a 4 X 4 Latin-square design. Steers were fed a concentrate diet at twice maintenance in 24 equal portions daily. Ruminal fluid dilution was measured using a single intraruminal infusion of cobalt-ethylenediamine tetraacetic acid (20 g) administered 9 h after the initial SF injection. Ruminal fluid was collected each hour during 8 to 24 h after the initial SF injection and analyzed for pH, osmolality and volatile fatty acids (VFA).(ABSTRACT TRUNCATED AT 250 WORDS)

Four esophageal- and ruminal-cannulated Angus steers (avg weight, 308 kg) were used to investigate how salivation is affected by the administration of purified slaframine (SF; 1-acetoxy-6-aminooctahydroindolizine), a cholinergic secretagogue isolated from Rhizoctonia leguminicola. Steers were fed a concentrate diet at twice the net energy requirement for maintenance in hourly increments. In trial 1, a single injection of SF was administered to four steers intramuscularly at 0, 6, 12 and 24-micrograms/kg body weight (BW) in a 4 X 4 Latin-square design. Saliva was collected via esophageal cannula at 15-min intervals 30 min after each feeding, weighted, sampled and reinfused via ruminal cannula over a 10-h period. At 12- and 24-micrograms SF/kg BW, salivary flow was 31 to 43% greater (P less than .01) than at 0- or 6-micrograms SF/kg. Response peaked within the first 3 h and returned to baseline levels at 8 h. Buffering capacity and pH of saliva were not different (P greater than .10); however, osmolality and Na concentration increased and K concentration decreased (P less than .10) as salivation rates increased. Feed intake of steers did not appear affected at any level of SF administration. In trial 2, 0-, 12- and 24-micrograms SF/kg BW were repeatedly administered intramuscularly to three steers in a 3 X 3 Latin-square design at 8-h intervals for 24 h. Salivary flow was measured and sampled over the entire 24-h period, as in trial 1. Flow rates were increased 50 to 70% (P less than .01) by SF treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Eighteen multiparous and 9 primiparous Holstein cows were used to determine the effects of a 13 and 23% crude protein concentrate on milk fat depression during early lactation. Beginning on d 22 postpartum, cows were fed a high fiber diet (27% acid detergent fiber) for 3 wk and then switched to a low fiber diet (9 to 10% acid detergent fiber) for 6 wk. Crude protein percentages calculated from dry matter consumption were 13.5 and 17.9% during the high fiber period and 12.7 and 22.3% during the low fiber period. Daily milk and fat yields for both primiparous and multiparous cows were greater for the high protein treatment. The magnitude of decline in milk fat percentage (from high to low fiber) was greater for the low protein treatment, as determined by nonlinear regression. The high protein treatment was more effective in reducing the severity of milk fat depression in primiparous cows than in multiparous cows. Dietary crude protein had no effect on milk protein or solids-not-fat percentages, rumen volatile fatty acid molar proportions, or serum acetate concentration. The mechanism by which the high protein ration minimized the fat depression response to low fiber rations by primiparous cows is unknown.