Metabolite flux across portal-drained viscera, liver, and hindquarters of hyperinsulinemic, euglycemic beef steers.

Metabolic response to i.v., exogenous insulin was characterized in three younger (355 d old, 340 kg BW) and four older (480 d old, 456 kg BW) beef steers. The steers had chronic indwelling catheters to allow measurement of blood flow and net flux of metabolites across portal-drained viscera (PDV), liver, and hindquarters (HQ). Daily N and ME intakes provided at least 1.8 times maintenance requirements. Net flux was measured before and after each steer received intramesenteric infusions of insulin, which ranged from 5 to 80 mU.h-1.kg BW-1, and intrajugular infusion of glucose to maintain euglycemia. Nonlinear fits of data provided predictions of maximal glucose entry (Rmax) for glucose infused, liver glucose release, HQ glucose uptake, and total glucose entry (TGE, sum of glucose infused plus liver release). Differences in BW could account for differences (P < .05) in Rmax for TGE between older steers (688 mmol/h) and younger steers (493 mmol/h). Plasma insulin needed to elicit half-maximal response (ED50) for TGE tended (P < .17) to be greater for older (82 mU/L) than for younger steers (49 mU/L). The decrease in liver glucose release in response to infusion of insulin was greater (P < .01) for older (-170 mmol/h) than younger (-106 mmol/h) steers. The ED50 for liver production of glucose tended (P = .13) to be greater for older (45 mU/L) than for younger (5 mU/L) steers. At 80 mU.h-1.kg BW-1, liver extraction of insulin decreased to approximately 50% of control extraction, and arterial insulin concentration was at least 9.4 times control concentrations. The PDV release and liver removal of L-lactate and propionate were not reduced by insulin infusion, although liver glucose release was 51 and 76% of control for younger and older steers, respectively. We concluded that older steers tended to be less sensitive than younger steers to the effects of insulin on glucose metabolism.

Effects of diet and housing density on growth and stomach morphology in pigs.

Two experiments were conducted to evaluate the impact of housing density on the stomach morphology of growing pigs and determine whether there was an interaction between housing density and diet. All diets were corn-soybean meal based. In Exp. 1, 42 barrows (41.0+/-.95 kg BW) were allotted either individually or three pigs per pen to evaluate the effects of crowding on stomach lesions. Pen space per pig was 1.54 and .51 m2, respectively. All pigs were fed a finely ground and pelleted diet (610 microm) for 6 wk. The ADG decreased (P<.05) for the pigs housed three per pen during wk 4 to 6 only. There was no effect of housing density on feed intake or gain/feed ratio. Neither visual nor histological ulcer score differed between the two treatment groups. No stomachs were graded as normal. In Exp. 2, 80 barrows (39.8+/-.9 kg BW) were allotted either two or four pigs per pen. Pen space per pig was .77 and .39 m2, respectively. Half of the pigs in each housing situation were fed a coarse meal diet (1,050 microm), and half of the pigs were fed a finely ground and pelleted diet (577 microm) throughout the 49-d experimental period. Throughout the trial, pigs housed two per pen gained at a greater rate (P<.05) than pigs housed four per pen. From d 14 to the end of the trial, pigs consuming the finely ground and pelleted diet gained at a greater rate (P<.05) than pigs fed the coarse meal diet. The differences in ADG were reflected in final body weight. Stomach weight as a percentage of body weight was higher for animals on the coarse meal diet. Visual and histological ulcer scores were similar, and both were higher (P<.001) on the finely ground and pelleted diet, indicating greater damage. There was no effect of space restriction on stomach morphology. These data show the major effect of diet type on stomach lesions with no interaction with space restriction.

Effects of diets differing in propensity to promote gastric lesions on defense systems in gastric mucosae.

The objectives were to characterize biochemical changes, focusing on the antioxidant defense system, in stratified squamous and oxyntic mucosae in pigs fed diets with differing propensity to promote gastric lesions. Barrows (n = 24; 48.7+/-1.0 kg BW) housed in individual pens were used in the experiment. Barrows were fed a corn-soybean meal diet. Half of the animals were fed the diet as a coarsely ground meal (CGM; average particle size = 886 microm), and half were fed the diet as a finely ground pelleted (FGP; average particle size = 528 microm) feed. Initiation and termination of the experiment were staggered over a 3-wk period. Diets were fed for 6 wk. Visual evaluation of the stratified squamous mucosa of the proximal stomach showed increased (P<.001) damage in animals fed the FGP diet. These results were supported by histological evaluation. Thiobarbituric acid-reacting substances (TBARS), indicative of peroxide generation, relative to amount of protein were higher (P<.001) in stratified squamous than in oxyntic mucosa, and, per unit of tissue, TBARS were highest in stratified squamous mucosa of animals fed the FGP diet. Glutathione peroxidase activity followed a pattern similar to that of peroxides. Prostaglandin E2 was higher (P<.004) in stratified squamous than in oxyntic mucosa. In contrast, the activity of catalase was higher (P<.001) in oxyntic mucosa and was not affected by diet. The data show differences in the production of peroxides, the antioxidant defense system, and PGE2 between stratified squamous and oxyntic mucosae. Generation of prooxidants and the antioxidant defense system may play a role in the predilection of ulcers for the stratified squamous mucosal region of the pig stomach.

Comparison of insulin infusion sites on metabolite net flux and insulin kinetics in growing euglycemic beef steers.

Four beef steers (average BW, 246 kg) were used in a split-plot design with five bovine insulin (I) infusion rates (5, 10, 20, 40, and 80 mU.kg-1.h-1) in the main plot and two infusion sites, mesenteric (M) and jugular (J) veins, in the subplot. Steers were fed a medium-energy diet at .235 Mcal of ME/kg BW.75 daily in 12 equal feedings at 2-h intervals. Catheters were placed in the mesenteric, hepatic-portal, and hepatic veins and in the abdominal aorta. Blood was sampled from the arterial, portal, and hepatic catheters at 20-min intervals for 1 h before I infusion. Glucose was infused intrajugularly to maintain euglycemia during the I infusion, with arterial glucose monitored at 10- to 15-min intervals. After at least 2.5 h, blood was again sampled at 20-min intervals for 1 h. Blood flow was determined by downstream dilution of p-aminohippurate. Arterial I concentrations (+/- SE) at the greatest I infusion rates were 183.5 +/- 10.46 (J) and 179.0 +/- 6.64 (M) microU/mL. Portal I concentration tended to be greater during M than during J infusion (e.g., J, 199.9 +/- 10.48 vs M, 225.8 +/- 8.99 microU/mL at the greatest dose). Hepatic glucose production at the larger three I doses reached a plateau near 40% of the preinfusion production rate (.57 +/- .02 mmol.kg-1.h-1 vs J, .23 +/- .029 and M, 27 +/- .037). Urea N concentration decreased, but portal uptake or hepatic release of urea N was largely unaffected by I dose or site of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of nutrient interchange and oxygen use among portal-drained viscera, liver, and hindquarters of beef steers from 235 to 525 kg body weight.

Our objective was to quantify changes in supply and use of nutrients and O2 by large-frame, multicatheterized beef steers as they grew from 235 to 525 kg BW. Steers consumed 5.25 to 9.87 kg DM/d of a 62% concentrate diet that provided 126 to 217 g N/d and 1 kg ADG. Steers were assigned to three groups (eight, nine, and eight steers each) that divided the BW range into thirds. Weights at first sampling for the three groups were 236, 319, and 445 kg, respectively. Each group was sampled twice. Groups were killed after the second sampling. Tissue weights and hindquarters (HQ) contents of fat, protein, and ash were measured. Blood flow, oxygen uptake, and net uptake or release of metabolites were regressed against functions of BW.75 to assess changes during growth. Blood flow in all tissues except liver and oxygen use by all tissues decreased per unit tissue weight as BW.75 and age increased. Changes with age per unit liver weight were as follows: decreased uptake of propionate and lactate, increased uptake of alpha-amino N and glutamine, decreased production of urea and glutamate, and increased production of acetate and beta-hydroxybutyrate. Glucose and urea production per unit liver weight was constant. Changes with age per unit HQ weight were as follows: increased uptake of glucose, decreased uptake of alpha-amino N and glutamate, decreased release of lactate, and increased release of glutamine. Weight of the portal-drained viscera (PDV) increased from 91 to 97 g/kg EBW as BW increased from 236 to 522 kg; PDV fat increased from 375 to 552 g/kg PDV tissues. Liver decreased from 16 to 12 g/kg EBW. Hindquarters decreased from 286 to 266 g/kg EBW; HQ protein was 200, 197, and 200 g/kg HQ tissue for Groups 1, 2, and 3, respectively. Corresponding fat was 131, 182, and 177 g/kg HQ tissue. Changes in net flux reflect changes in nutrient partitioning and tissue deposition as steers grew and aged.

Physiological responses in swine treated with water containing sodium bicarbonate as a prophylactic for gastric ulcers.

Maintenance of gastric pH above 4.0 aids the prevention of bile acid-mediated ulcerative damage to the pars esophageal tissue in pigs. One means of doing so is the addition of buffering compounds, such as sodium bicarbonate, to the water supply; however, any potential physiological effect of buffer consumption has yet to be determined. Experiment 1 tested the acute effects of buffer addition to the water supply on systemic acid-base and electrolyte balance in swine (BW 40.7 +/- 3.0 kg). Consumption of water calculated to a 200 mOsm solution with sodium bicarbonate for 24 h increased (P < 0.05) blood Na+, HCO3(-), and pCO2, although these effects were all within physiologically tolerable levels. Urine pH and Na+ excretion increased (P < 0.001) following the consumption of NaHCO3, with Na+ concentration almost threefold higher in treated pigs compared with controls. Experiment 2 determined the chronic systemic effects of buffer consumption by measuring blood and urine variables, with pigs consuming NaHCO3-treated water throughout. Water consumption increased (P < 0.001) during buffer consumption, although intake levels remained within normal ranges. Blood pH levels were not affected by long-term consumption of dietary buffer; however, blood HCO3(-) (P < 0.05), Na+, and pCO2 (P < 0.01) increased. Urine pH and urine Na+ concentration increased (P < 0.01) in buffer-treated compared with control animals. Results indicate that sodium bicarbonate can safely be added to the water supply for pigs, with no clinically relevant alterations in acid-base balance because the animals readily compensate for buffer intake.

Insulin sensitivity and responsiveness of portal-drained viscera, liver, hindquarters, and whole body of beef steers weighing 275 or 490 kilograms.

Our objective was to quantify effects of age, weight, and body composition on responsiveness (Rmax or Rmin) and sensitivity (ED50) of several parameters of glucose metabolism to insulin in growing beef steers. Steers ate equal-sized meals every 2 h; the diet contained 62% concentrate and sustained 1 kg ADG. Treatments were euglycemic clamps at 10, 20, 40, 80, 160, and 320 mU.h-1.kg BW-1 of insulin infused into a mesenteric vein of seven younger (275 kg BW) and seven older (490 kg BW) steers. Most steers received three of the six treatments; two extra steers were added to compensate for missing data. Steers had blood vessel catheters and ultrasound flow probes that allowed measurement of net uptake or release of glucose and insulin by portal-drained viscera (PDV), liver, and hindquarters (HQ). Steady-state glucose infusion rate (SSGIR) was intrajugular glucose infused during treatments to maintain euglycemia. Within age groups, Rmax or Rmin and ED50 were estimated by nonlinear regression of glucose flux on arterial plasma insulin concentrations. Steers were killed after sampling, tissues were weighted, and HQ content of fat and protein was determined. Those data were used to predict tissue weights and HQ composition at the time of the euglycemic clamps. Predicted EBW (243 vs 444 kg), liver (4.24 vs 6.19 kg), and HQ (73 vs 122 kg) were heavier for older than for younger steers. Fat in HQ was higher for older than for younger steers (173 vs 134 g/kg), but protein was similar (198 g/kg). The ED50 (mU of insulin/L of plasma) for SSGIR (237 +/- 65 vs 113 +/- 22), liver glucose release (89 +/- 22 vs 44 +/- 11), total glucose entry (418 +/- 184 vs 125 +/- 20), and HQ glucose uptake (488 +/- 151 vs 243 +/- 78) was higher for older than for younger steers. The Rmax (mmol glucose.h-1.kg tissue-1) for SSGIR (2.68 +/- .22 vs 2.09 +/- .23) and HQ (3.08 +/- .33 vs 2.46 +/- .30) was higher for younger than for older steers. Liver glucose release decreased in response to insulin; Rmin (mmol glucose.h-1.kg liver-1) was higher for younger (36.0 +/- 6.9) than for older (24.7 +/- 3.2) steers. We conclude that as steers grew older, heavier, and fatter, their peripheral tissues and liver became less sensitive and less responsive to insulin.

Portal blood flow in beef steers: comparison of techniques and relation to hepatic blood flow, cardiac output and oxygen uptake.

We compared two techniques for measuring blood flow through portal-drained viscera (PDV) of beef steers and measured portions of cardiac output and total oxygen uptake attributable to PDV and hepatic tissues. Four steers (198 +/- 2 kg), equipped with chronic catheters in appropriate vessels, a transit-time ultrasound probe around the hepatic portal vein and a temporary cardiac output thermodilution catheter, were fed a 60:40 hay: concentrate diet. Treatments, designed to alter blood flow, were: 12 equal meals every 2 h (CNTL); CNTL plus 2 mg clenbuterol in one meal (CLEN); and a 65-h fast (FAST). Blood flow through PDV was measured by dilution of p-aminohippurate (PAH) and transit-time ultrasound. Hepatic blood flow was measured by PAH dilution and cardiac output was measured by thermodilution. Blood flow measured by transit-time ultrasound was consistently slower (45%, P less than .01) than blood flow measured by PAH dilution. Necropsy revealed anatomical constraints that precluded proper placement and function of the flow probes. Cardiac output (liters/h) was greater (P less than .05) for CLEN (3,082) than for CNTL (1,655) or FAST (1,047). Percentage of cardiac output flowing through PDV and hepatic tissues was less (P less than .05) for CLEN (23 and 24%) than for CNTL (31 and 38%) or FAST (32 and 38%). Whole body oxygen uptake (mmol/h) was greatest (P less than .05) for CLEN (4,220), intermediate for CNTL (2,999) and least for FAST (1,965). Percentage of oxygen uptake attributable to hepatic tissues was greater (P less than .05) for FAST (31%) than for CLEN (18%), with CNTL intermediate (24%). Percentage of oxygen uptake attributable to PDV (22%) was not affected (P greater than .05) by treatments.

Effects of dietary clenbuterol on metabolism of the hindquarters in steers.

The objective of this study was to measure acute (d 1) and chronic (d 9) effects of dietary clenbuterol on heart rate, blood flow, oxygen uptake, and net uptake/release of metabolites in the hindquarters of growing steers. The design was a single reversal with two 9-d periods of control or 8 mg clenbuterol/d with 5 d between periods. Within 2 h of initial consumption of 2 mg clenbuterol (d 1), heart rate and blood flow doubled and arterial plasma concentrations of glucose, L-lactate and nonesterified fatty acid (NEFA) increased, whereas alpha-NH2 N and NH3 concentrations decreased, demonstrating an acute response. Uptake of oxygen increased and net uptake of alpha-NH2 N decreased. Net release of both L-lactate and NEFA increased. On d 9, there were no acute responses to clenbuterol consumption; however, heart rate, blood flow, and NEFA concentration remained chronically elevated, and plasma concentrations of acetate and propionate decreased compared with control feeding. Net uptake of alpha-NH2 N, oxygen and release of L-lactate by the hindquarters chronically increased on d 9 of clenbuterol feeding. Changes in both blood flow and arteriovenous (AV) concentration difference contributed to changes in uptake/release. The chronic metabolic changes and oxygen uptake were consistent with increased N retention in the hindquarters through increased protein synthesis, decreased use of acetate and increased reliance on NEFA for cellular energy. In conclusion, the data show that the perturbation of homeostatic regulation by dietary clenbuterol on d 1 evolved to establishment of homeorhetic regulation by d 9 that is consistent with increased skeletal protein accretion in growing steers.

Technical note: comparison of techniques for measurement of oxygen uptake by cattle.

The objective of this study was to compare techniques for measuring whole-body O2 uptake of steers. Oxygen uptake provides a basis for evaluating metabolic energy expenditure. We measured O2 uptake as the product of the difference in O2 contents of incoming and exhaust air times air flow through a respiration calorimeter (head box). Additionally, we used catheters and thermistors placed into the blood vessels near the heart to measure cardiac output and whole-body O2 uptake. The cardiac output measurement system used thermodilution to measure the blood flow rate through the pulmonary artery. Catheters placed in the pulmonary artery and in the aorta provided respective samples of oxygen-depleted and oxygen-enriched blood. The product of blood flow rate times blood oxygenation by the lungs provided the basis for calculating total O2 uptake. Four sets of simultaneous measurements with the two techniques were made on eight steers weighing from 272 to 528 kg. Oxygen uptake was not different (P > .20) for the two techniques. Overall (mean +/- SEM) O2 uptake measured by cardiac output (117.2 +/- 7.0 L/h) was 97 +/- 3% of O2 uptake measured by respiration calorimetry.

Level of nutrition and splanchnic metabolite flux in young lambs.

Splanchnic metabolite flux was measured in young lambs given access to a high-concentrate diet either ad libitum (ADLIB) or at a maintenance level (MAINT) for 21 d. Net fluxes of urea N (UN), ammonia N (NH3 N), alpha-amino N (AAN), amino acids, glucose (G), and lactate (L) across the liver and portal-drained viscera (PDV) were measured in 11 crossbred ram lambs (35 kg) surgically fitted with indwelling catheters in the portal, hepatic, and mesenteric veins and mesenteric artery. During the 21-d period, daily N and ME intakes were 24.6 and 10.7 g N/d and 3.02 and 1.28 Mcal/d, respectively, for ADLIB and MAINT lambs. Intakes, thus, were 42% lower for MAINT than for ADLIB lambs. Net portal fluxes of UN, NH3 N, AAN, and L in MAINT lambs were 46%, 84%, 50%, and 74%, respectively, of that in ADLIB lambs. Expressed as a percentage of N intake, the proportion of AAN absorbed by the PDV was higher in MAINT lambs (P less than .05) than in ADLIB lambs. There was no net portal glucose absorption in either group of lambs; however, net hepatic glucose production in MAINT lambs was 48% of that in ADLIB lambs. There was net utilization of glutamine by the PDV; net glutamine flux in MAINT lambs was 49% of that in ADLIB lambs. The liver utilized AAN and NH3 N and produced UN. Splanchnic tissues modulate metabolite flux following changes in feed intake in young ruminants.

Changes in gastric contents in pigs fed a finely ground and pelleted or coarsely ground meal diet.

The objective was to characterize the change in stomach contents in relation to time after feeding between pigs consuming a restricted amount of a finely ground and pelleted (FGP) or coarsely ground meal (CGM) diet. Particular interest was placed on the concentration of organic acids and ammonia, the products of microbial fermentation. Thirty barrows were ranked by weight and assigned to a postfeeding time of 2, 4, 6, 8, or 12 h and either the FGP or CGM diet. Initiation and termination of the experiment were staggered over a 2-wk period. The treatment period was 42 d. Percentage of dry matter was higher (P<.01) in the stomach contents of pigs on the CGM diet. Concentrations of pepsin and protein were higher (P<.05) and ammonia tended to be higher (P = .10) in the proximal stomach of pigs fed the FGP diet. In contrast, concentrations of acetate and L-lactate were higher (P<.05) in the proximal stomach of pigs fed the CGM diet. All pigs on the CGM diet had stomachs that graded as normal on visual inspection. There was variable damage to the stomachs of pigs on the FGP diet. Measurement of chromium concentration in the stomach after an oral dose of Cr-EDTA clearly demonstrated the mixing that occurs between the proximal and distal stomach by 2 h after feeding in pigs consuming the FGP diet, whereas a gradient was maintained in pigs consuming the CGM diet. Thus, components normally secreted in the distal stomach return to the proximal stomach. These data show that components secreted in the distal region, such as acid and pepsin, may play a role in initiating damage to the stratified squamous mucosa. High concentrations of organic acids in the stomach of pigs on the CGM diet were not associated with damage to the stratified squamous mucosa in the esophageal region.

The influence of high-nitrogen forages on the voluntary feed intake of sheep.

The objective of this research was to examine the effect of high concentrations of nonprotein nitrogen (NPN) on the voluntary food intake of sheep fed high-quality grasses. Wether lambs (n = 6 per treatment) were fed dried switchgrass (Panicum virgatum L.; Exp. 1) or dried tall fescue (Festuca arundinacea Schreb.; Exp. 2). In both experiments, urea was added to the dried forage at 0 (control), 12, or 24 g of N/kg of DM to increase the NPN concentration. Acid detergent fiber concentrations were 305 g/kg of DM in both experiments, although DM digestibility was 663 and 618 g/ kg of DM in Exp. 1 and Exp. 2, respectively. Voluntary feed intake of the control forage was 28.2 and 19.1 g/ kg of BW in Exp. 1 and Exp. 2, respectively, and decreased for the high-urea treatments to 25.2 and 16.2 g/kg of BW in Exp. 1 (P = 0.07) and Exp 2 (P = 0.03), respectively. Total feed N concentrations increased from 29.5 g to 45.7 g of N/kg of DM in Exp. 1 (P < 0.01) and from 28.4 to 55.9 g of N/kg of DM in Exp. 2 (P < 0.01). Nonprotein N concentrations increased from 28.3 to 53.8% of the total N in switchgrass diets (Exp. 1; P < 0.01), and from 26.4 to 64.0% in tall fescue diets (Exp. 2; P < 0.01). Plasma urea concentrations of the lambs increased from 3.1 to 6.6 mM (Exp. 1; P < 0.01) and from 2.9 to 5.8 mM (Exp. 2; P < 0.01) as the amount of urea added to the diets increased. These changes resulted in an increase in plasma osmolality from 298 to 307 mOsm/kg (Exp. 1; P = 0.04), and from 299 to 307 mOsm/kg (Exp. 2; P = 0.06). Increasing feed N and NPN concentrations through the addition of urea caused a significant decrease in the voluntary feed intake of sheep fed tall fescue and switchgrass. These responses showed no significant cause-and-effect relationship between voluntary feed intake, plasma urea concentrations, and plasma osmolality.

Absorption, plasma flux and oxidation of L-leucine in heifers at two levels of intake.

Four Hereford X Angus heifers (379 +/- 11 kg) with indwelling hepatic portal vein, iliac artery and mesenteric vein catheters were used in a switchback design to measure net portal absorption of leucine at two levels of energy intake, 130 and 260 kcal metabolizable energy.(kg.75.d)-1. Nine hourly measurements were made through two consecutive 4-h feeding periods on each heifer at each intake level. In separate experiments, N balance was determined and 6-h continuous infusions of L-[1-14C]-leucine were used to measure total plasma flux and oxidation of leucine with two of these heifers, one at each level of intake, and one additional Hereford heifer at both levels of intake. Net portal absorption of leucine increased with increasing intake from 5.4 to 12.4 mmol/h, and was associated with average leucine flux and oxidation rates of 30.7 and 4.7 mmol/h at low intake and 49.9 and 8.8 mmol/h at high intake. Protein synthesis (flux - oxidation) and protein accretion (N balance X 6.25) averaged 1,367 and 39 g/d at low intake and 2,156 and 219 g/d at high intake, respectively. Percent contributions of absorption and oxidation to total leucine flux were 17.6 and 15.3 at low intake and were 24.9 and 17.6 at high intake, respectively.

Nitrogen and protein metabolism and metabolites in plasma and urine of beef steers treated with somatotropin.

The objectives of this study were to determine the effects of daily injection of bovine somatotropin (bST) on the metabolism of N and 1-[14C]leucine and on hormone and metabolite concentrations in growing beef steers. Injection of bST increased N retention (P less than .05) primarily through decreased (P less than .10) urinary N excretion. Plasma concentration of somatotropin, insulin and glucose increased (P less than .01) and of urea-N (P less than .01) and alpha-amino-N (P less than .10) decreased with bST compared with excipient injection. Total leucine flux was not altered by treatment; however, the partition of flux was. Leucine oxidation decreased (P less than .05) and leucine used for protein synthesis (P less than .10) increased, with bST compared with excipient injection. During excipient injection, 10.3 g protein were synthesized for each gram crude protein deposited, whereas during bST injections only 6.4 g were required. The average maximum contribution of myofibrillar protein degradation to whole body protein degradation, calculated from excretion of 3-methylhistidine, was 16%. Although the ratio of protein deposition/protein synthesis was low for both excipient- and bST-injected steers, the incremental efficiency of protein deposition was 50%, reflecting a dilution of protein synthesis required for turnover and a proportionately greater increase in protein synthesis than protein degradation with bST injection. In growing beef steers, bST stimulated whole body protein synthesis and decreased leucine oxidation. The change in partition of leucine flux, but not of total flux (irreversible loss), demonstrates a chronic redirection in metabolism consistent with homeorhetic control. These data from steers injected with bST suggest mechanisms by which bST affects metabolism during normal growth.

Effects of feed physical form and buffering solutes on water disappearance and proximal stomach pH in swine.

The effects of the physical form of feed on water disappearance and the effects of buffered water on proximal stomach pH in swine were determined in two experiments. In Exp. 1, 32 barrows were used to evaluate the water disappearance in pigs fed a finely ground and pelleted diet vs those fed a coarsely ground and mashed diet for ad libitum consumption over a 2-wk interval. There were four replicates with eight pigs per replicate. Average daily water and feed disappearance did not differ (P = 0.06 and P = 0.10, respectively). However, average daily water to feed ratio was higher for pigs on the pelleted diet (4.21+/-0.31 L/kg vs 3.04+/-0.33 L/kg; P = 0.02). The higher ratio for the pelleted diet indicated that this may be the cause of a more fluid digesta allowing reflux of irritants from the distal stomach to damage the pars esophageal region of the proximal stomach. In Exp. 2, four barrows (25+/-2 kg) had gastric cannulas surgically implanted into the proximal region of the stomach. Pigs were given ad libitum access to a finely ground and pelleted diet. The experimental design was a Latin square. Water treatments included water (control), 200 mOsm NaHCO3, 250 mOsm NaHCO3, and 250 mOsm mono-dibasic sodium phosphate. Pigs were given a 4-d adjustment period, and pH measurements began on the morning of the 5th d and continued for 24 h under normal feeding conditions. Feed was removed and measurements were continued for 16 h. Buffered water raised the pH of the proximal region of the stomach compared to the control (P < 0.001). Average pH while consuming the water treatments was 3.65+/-0.11 (n = 4) for water control, 4.86+/-0.11 (n = 4) for the 200 mOsm NaHCO3, 4.63+/-0.11 (n = 4) for the 250 mOsm NaHCO3, and 4.59+/-0.14 (n = 3) for the 250 mOsm mono-dibasic sodium phosphate. Buffers also raised the pH of the proximal region of the stomach for the fed (P < 0.001) and the feed restriction (P < 0.01) phases of the trial. Water disappearance rates in pigs given NaHCO3 were higher than in the control (P < 0.01). Average daily water disappearance for the treatments was 9.13+/-0.74 L for the control, 13.56+/-0.74 L for 200 mOsm NaHCO3, 13.77+/-0.74 L for the 250 mOsm NaHCO3, and 10.33+/-0.95 L for the phosphate buffer. The proximal pH of the stomach was increased by adding buffers to the water supply. Addition of NaHCO3 buffers also caused increased water disappearance.

Evaluation of a role for prolactin in growth and the photoperiod-induced growth response in sheep.

An experiment was conducted to determine whether prolactin is involved in growth or in mediating the photoperiod-induced growth response in sheep. Prolactin was manipulated by im injections of 2-Br-alpha-ergocryptine (CB154) or sc injections of ovine prolactin (oPRL) and by two light:dark regimens (16L:8D and 8L:16D). Fifty-six wether lambs (two/pen) were allotted to one of four treatments for a 9-wk growth study. Treatments were: 1) 16L:8D, placebo injections; 2) 16L:8D, CB154 injections; 3) 8L:16D, placebo injections and 4) 8L:16D, oPRL injections. Daily injections of CB154 (.1 mg/kg body weight.75), oPRL (.8 mg/kg body weight.75) or placebo were in 1 ml volume. Animals were fed ad libitum a complete mixed diet. At wk 8, plasma prolactin concentrations at 3 to 6 h postinjection were 214, 3, 90 and 228 ng/ml for treatments 1, 2, 3 and 4, respectively. Pattern of feed intake, measured at 8-h intervals for a 48-h period, was affected by photoperiod. Animals exposed to the 16L:8D photoperiod consumed 40.0, 42.4 and 17.6% of their total daily feed intake during the first 8 h of light, second 8 h of light and 8 h dark interval, respectively. Those exposed to the 8L:16D regimen consumed 55.2, 22.2 and 22.6% during their 8-h light interval, first 8 h of dark and second 8 h of dark, respectively. Both cumulative gain and feed intake were greater in 16L:8D control animals than in those animals receiving CB154.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of photoperiod and prolactin on body composition and in vitro lipid metabolism in wether lambs.

An experiment was conducted to determine the possible effects of photoperiod and prolactin on the physical and chemical composition of body weight gain. Prolactin was manipulated by im injections of 2-Br-alpha-ergocryptine (CB154) or sc injections of ovine prolactin (oPRL) and by two light:dark regimens (16L:8D and 8L:16D). The four treatments employed were: 1) 16L:8D, placebo injections; 2) 16L:8D, CB154 injections; 3) 8L:16D, placebo injections and 4) 8L:16D, oPRL injections. After a 9-wk growth study, animals were slaughtered at similar body weights over the next 2-wk period. Weight of intestines was directly related and weight of pelt inversely related to circulating concentrations of prolactin. Content of N and lipid in the carcass was not influenced by treatment. However, N content of the noncarcass components was elevated (P less than .01) in animals receiving CB154. In vitro rates of acetate incorporation (nmol X 100 mg tissue-1 X 3 h-1) were higher in subcutaneous than in perirenal adipose tissue (1,920 vs 777; P less than .001). Rates for treatments 1, 2, 3 and 4 were 1,770, 953, 1,350, respectively. The rate for treatment 1 was greater than that for treatments 2 (P less than .001) and 3 (P less than .05). There was no stimulation of lipogenesis in response to insulin added to the incubation medium. In vitro rates of glycerol release (nmol X 100 mg tissue-1 X 2 h-1) were higher in perirenal than in subcutaneous adipose (135 vs 81; P less than .001). The respective treatment rates were 120, 84, 104 and 124, with treatment 1 being greater (P less than .05) than treatment 2. Epinephrine addition elevated glycerol release (156 vs 60; P less than .001). Differences for in vitro lipid metabolism between the perirenal and subcutaneous depots were independent of differences in cell size. Overall, these data indicate that the increased body weight gain due to extended lighting was not accompanied by detrimental effects on carcass composition. Nor was there any clear relationship between circulating concentrations of prolactin and in vitro lipid metabolism.

Eicosapentaenoic and docosahexaenoic acids increase insulin sensitivity in growing steers.

An experiment was conducted to determine the effect of dietary n-3 long chain PUFA on insulin sensitivity in growing steers. Steers (n = 12, initial BW = 336.3 kg, SEM = 7.7) were adapted to a basal diet that was 70% concentrate mix and 30% orchardgrass hay. Steers were fed a daily amount of 0.26 Mcal ME per kg BW (0.75). After 3 wk steers were transitioned to 1 of 2 treatment (Trt) diets (n = 6 per diet) containing added Ca salts of fatty acids at 4% of DM using a source of fat that was enriched in n-3 fatty acids, including eicosapentaenoic acid and docosahexaenoic acid (FOFA), or a source of fat without n-3 fatty acids and a greater percentage of C16:0 and C18:1 (LCFA). Three intravenous (i.v.) glucose tolerance tests (IVGTT) were conducted, 1 during the basal diet, and 2 after transition to treatment diets at time 1 (T1; d 4 Trt) and time 2 (T2; d 39 Trt). Three i.v. insulin challenge tests (IC) were conducted the day after each IVGTT. Measurements on the basal diet were used as covariates. For IVGTT, there was a diet by time interaction (P < 0.05) for glucose area under the response curve (AUC). The AUC50 (mM glucose × 50 min) at T1 was less (P = 0.02) for LCFA (126.2) than FOFA (151.8), AUC50 at T2 tended to be greater (P = 0.07) for LCFA (165.9) than FOFA (146.0). Preinfusion insulin concentration was greater (P < 0.001) before the IVGTT and IC for steers fed LCFA (40.4 and 40.2 µIU/mL) than for steers fed FOFA (23.7 and 27.1 µIU/mL), respectively. Glucose clearance did not differ between treatments. For IC, minimum glucose concentration was greater (P = 0.02) and glucose AUC150 was less (P < 0.01) for steers fed LCFA than for steers fed FOFA. Values for glucose concentration were 1.8 mM and 1.5 mM and for AUC150 (mM glucose × 150 min) were 203.1 and 263.6 for steers fed LCFA and FOFA, respectively. Insulin clearance (fraction/min) was greater (P < 0.01) for steers fed LCFA (0.121) than FOFA (0.101). The insulin AUC60 (µIU/mL × 60 min) postinfusion was less for LCFA (17,674) than FOFA (19,997), and tended to be greater (P = 0.06) at T1 (19,552) than T2 (18,119). Plasma NEFA concentrations at T2 during IVGTT were greater (P < 0.05) in steers fed FOFA than in steers fed LCFA. The results indicated that supplementing with long-chain n-3 PUFA (FOFA) increased insulin sensitivity in growing steers compared with feeding a supplement with greater concentration of SFA (LCFA).