Nonesterified fatty acids (NEFA) are measured routinely in the study of nutrition and growth physiology. To improve the efficiency with which this variable is measured, a two-reaction, enzymatic-based assay was adapted and validated to quantify NEFA in bovine blood plasma using 96-well microtiter plates. The effects of incubation time, temperature, and of sample volume were examined in addition to possible interfering substances, recovery, reagent stability, and range of linearity. Incubation for 30 min at 21 degrees C for each of the two reactions resulted in maximal slope and r2 values (1.94 and .999, respectively). Percentage of recovery was 107% when using 5 microL and 100% when using 10 microL of heparinized bovine plasma in the assay. Uniform linear standard curves (r2 > .99) were obtained using reagents stored at 4 degrees C for 9 d. An equal volume of 1 mM acetate, propionate, valerate, and butyrate added to plasma did not affect results. The assay was linear from 125 to > 1,000 microEq/L. Intra- and interassay CV for the 5-microL sample volume were 3.6 and 3.7%, respectively. This modified assay provides results comparable to the standard assay yet reduces reagent and labor requirements and increases sample capacity.

Crossbred steers (n = 20; 316 +/- 4 kg BW), each fitted with a ruminal cannula, were used to evaluate the effects of acute acidosis (AA) and subacute acidosis (SA) on DMI, ruminal fermentation, blood chemistry, and endocrine profiles. Animals were blocked by BW and assigned to treatments including 1) intraruminal (via cannula) steam-flaked corn (3% of BW; AA); 2) intraruminal dry-rolled wheat:dry-rolled corn (50:50; 1.5% of BW; SA); 3) offering forage-adapted steers ad libitum access to a 50% concentrate diet (AA control; AC); and 4) offering 50% concentrate diet-adapted steers ad libitum access to a 50% concentrate diet (SA control; SC). Samples of ruminal fluid and whole blood were collected on the day of the challenge (d 0) and 3, 7, 10, and 14 d after the challenge. Daily DMI responded quadratically (P < 0.01) through d 7 for AA and SA steers and increased linearly (P < 0.01) for AC steers. Dry matter intake by AA steers reached a nadir (< 3 kg/d) on d 3 and gradually increased to a level similar to other treatments (7 kg/d) by d 10, whereas DMI by SA steers increased through d 3. Blood pH, bicarbonate, base excess, and total CO2 were decreased (P < 0.03) for AA steers and increased (P < 0.03) for SC steers through d 7. Ruminal pH decreased quadratically (P < 0.01) in AA and AC steers and increased (P = 0.01) in SA steers through d 7. Ruminal total lactate concentration and osmolality responded quadratically (P < 0.01) for AA and AC steers. Ruminal total lactate peaked on d 3 for AA steers and on d 0 for AC and decreased to basal concentrations by d 7. Plasma NEFA concentration increased (P < 0.04) on d 3 and 7 for AA steers. Serum Na decreased (P < 0.05) on d 0 for AA and SA steers and on d 7 and 14 for AA steers. Serum P decreased (P = 0.01) for AA steers through d 7 and decreased quadratically (P = 0.01) for AC steers through d 7. Serum albumin and cholesterol decreased (P < 0.02) for AA and AC steers through d 7. Area under the GH curve decreased (P = 0.02) for AA and AC steers through d 7. Considerable variation was evident in the ability of an animal to cope with a carbohydrate challenge. Results of data modeling generally suggest that serum amylase activity, cholesterol and potassium concentrations, and plasma NEFA concentrations were useful in distinguishing between steers classified as experiencing subacute acidosis or not affected by a carbohydrate challenge.

Twenty (12 Holstein, 8 Longhorn cross) calves (198 kg and 7 mo old) were used in a randomized complete block design to evaluate the effects of dietary forage concentration and feed intake on carbohydrase activities and small intestinal (SI) morphology. Calves were individually fed 90% forage (alfalfa) or a 90% concentrate (50% sorghum: 50% wheat) diet at either one or two times NEm for 140 d and slaughtered; tissues and small intestinal digesta were collected. Increased feed intake increased (P less than .05) pancreatic weight, alpha-amylase and glucoamylase activities in the pancreas, SI length and SI digesta weight. Forage-fed calves gained faster (P less than .01) and had greater (P less than .05) pancreatic protein concentrations, alpha-amylase and glucoamylase activities in the pancreas and greater SI digesta alpha-amylase activities than grain-fed calves did. Increased feed intake increased (P less than .01) mucosal weight/cm small intestine only in forage-fed calves and increased (P less than .05) SI surface/volume only in grain-fed calves. Mucosal weight was greatest (P less than .05) at the terminal ileum, surface/volume was greatest (P less than .05) in the duodenum, and mucosal protein concentration was highest (P less than .05) in the SI mid-section. Mucosal lactase was higher (P less than .05) in proximal segments, whereas mucosal isomaltase was higher in middle and distal segments of the small intestine. For mucosal maltase activity, there was a feed intake x SI sampling site interaction (P less than .05) and for trehalase, a diet x feed intake x SI sampling site interaction (P less than .05). The SI distribution patterns of maltase and isomaltase were similar, as were those of trehalase and lactase. The alpha-amylase activity in the pancreas and SI morphology were influenced greatly by diet composition and feed intake by calves.

Lipid accretion and metabolism during accelerated gain and growth hormone administration were examined in a 29-d trial with 24 beef steers. Treatments in this 2 X 2 factorial design consisted of level of feeding (restricted or ad libitum) and exogenous hormone [pituitary-derived bovine growth hormone (GH) at 38 IU/d or excipient]. Live weight gain was not affected by hormone treatment. Protein content of the 9-10-11th rib section was greatest in steers receiving GH irrespective of feeding level, whereas a reduction of lipid content due to GH was seen only with ad libitum feeding. Restricted-fed steers had the highest plasma concentrations of free fatty acids (FFA), and only at this feeding level did GH treatment result in further elevation of FFA concentrations. In vitro rates of adipose lipogenesis, esterification and lipolysis were greatest in tissue from ad libitum-fed steers. The only effect of GH on in vitro metabolism was a tendency for lower lipolytic rates with ad libitum feeding. GH did not affect adipocyte size. The mechanism for the effect of GH on lipid deposition could not be determined from incubations of adipose slices from chronically treated steers, although enhanced responsiveness to an in vivo lipolytic challenge was observed. By inference, substrate availability appears to determine the productive responses to GH.

Six crossbred steers (261 +/- 18 kg BW) fitted with hepatic portal, mesenteric venous and arterial catheters, and duodenal, midjejunal, and ileal cannulas were used in a replicated 3 x 3 Latin square design to determine the effect of varying levels and site of glucose plus 2-deoxyglucose (2DG) infusion on net portal-drained visceral flux. Steers were fed chopped alfalfa in six equal portions daily at 1.5% of BW. Glucose (0, 9, or 18 g/h) and 2DG (0, 1, or 2 g/h) were infused continuously through the duodenal or midjejunal cannula (two infusion sites) at total glucose plus 2DG infusion rates of 0, 10, or 20 g/h. Arterial and portal blood samples were taken simultaneously at 20-min intervals from 5 to 9 h of infusion. Portal blood flow was determined by continuous infusion of p-aminohippurate and net flux was calculated as venous-arterial concentration (PA) difference times blood flow. Arterial concentration of glucose was not affected (P > .10) by glucose plus 2DG infusion, whereas arterial concentration of 2DG was greater (P < .05) when glucose plus 2DG was infused into the duodenum and increased (linear, P < .10) as amount of glucose plus 2DG infused into both the duodenum and midjejunum increased. Net portal flux and PA difference of glucose and 2DG were greater (P < .05) when glucose plus 2DG was infused into the duodenum. Although 2DG was infused at 10% of the total glucose plus 2DG infusion, it accounted for only 1.7 and .7% of the glucose plus 2DG appearing in portal blood when glucose plus 2DG was infused at 10 and 20 g/h, respectively. We conclude that glucose is more readily absorbed across the proximal-half than the distal-half of the small intestine, and that passive diffusion is a minor route of glucose absorption.