Studies were conducted to define steady state pH, propionic acid concentrations and fluid turnover in the rumen of steers fed every 3 h and to determine whether rates of ruminal propionic acid disappearance were linearly related to their in situ production rates. Ruminally fistulated beef steers (326 +/- 11 kg; n = 3) were fed eight times daily a 54% mixed hay: 46% corn-based concentrate diet to meet maintenance energy requirements. Maximal acceptable variations from the mean at steady state conditions of pH, propionic acid concentrations and specific activity, and liquid flow (Cr marker concentrations) were defined as 4%, 20%, 30% and 10%, respectively, across 4 h of observation. In situ production of propionic acid, determined by pulse-continuous infusion of 1-14C-propionic acid, was 142 mmol/h (CV = 8.4%). The ruminal half-life of propionic acid was estimated to be 1.5 h and the liquid flow rate was 3.8 liters/h. Propionic acid production rates subsequently were elevated by continuous intraruminal infusion of buffered propionic acid. Irrespective of production (basal and infusion) rate, approximately 66% disappeared (i.e., presumed absorption) and 34% passed from the rumen to the lower tract in the liquid phase. Ruminal disappearance of propionate was linearly related with its production rate, and propionate concentrations and production rates also were linearly related. Liquid passage was linearly related to production rate, but there was insufficient evidence to conclude that fractional dilution rate or ruminal volume were similarly related. When ruminal production of propionic acid is elevated, the rumen has additional absolute capacity to remove propionate, but the fractional removal appears to be constant. The digestive tract distal to the rumen is likely an important site of propionate absorption in cattle when propionate production is high.

Disappearance of acetic acid was quantified to determine whether removal of this acid from the reticulorumen is altered when ruminal acetic acid concentrations are elevated. Ruminally fistulated beef steers (n = 3 per experiment; BW = 320 +/- 9 kg) were fed eight times daily a 46% corn-based concentrate:54% mixed hay diet to meet maintenance energy requirements (3.5 kg of DM/d). In situ production of acetic acid, determined by pulsed-continuous infusion of [1-14C]acetic acid, was 530 mmol/h (CV = 12%). Disappearance from the reticulorumen (i.e., presumed absorption) was 460 mmol/h (CV = 2%) or 87% (CV = 2%) of ruminal production. Variation is described within an operational steady state. Acetic acid concentrations were increased by continuous infusion of unlabeled acetic acid into the reticulorumen. Ruminal disappearance (mmol/h) increased when this simulated production was elevated up to and exceeding in situ rates reported previously (530 to 2,700 mmol/h). These data suggest that two-thirds to three-fourths of ruminal acetate production disappeared across the reticuloruminal wall when concentration was elevated; the complement exited from the rumen with the liquid phase. The reticulorumen has an additional capacity to remove acetic acid; however, it does so with an apparent reduced efficiency at higher production rates. Liquid out-flow may affect the efficiency of reticuloruminal disappearance. Sites distal to the rumen become quantitatively important when ruminal acetic acid concentrations are increased.

Studies were conducted to determine the disappearance of propionic acid from the rumen and across the small intestine. Four crossbred beef steers, fitted with ruminal, duodenal and ileal cannulas, were given pulsed-continuous infusions of a nonabsorbable liquid phase marker (CrEDTA) and buffered propionic acid to achieve ruminal propionate productions (RPP) of 142 (basal), 567 and 997 mmol/h. Liquid flows from the rumen, and at the duodenum and ileum (2.75, 3.57 and .92 liters/h, respectively) were not affected by RPP (P greater than .23), although significant differences existed between sites (P = .001), reflecting a net addition of liquid between the rumen and duodenum and a net removal of liquid within the small intestine. Propionate disappearance from the rumen was 40 to 57% irrespective of RPP, with the complement passing from the rumen. Of the propionate that exited the rumen, 93 to 97% disappeared prior to entering the duodenum. Overall removal of RPP prior to the duodenum was 97 to 99% irrespective of RPP. Passage of propionic acid at the duodenum and at the ileum did not differ (P greater than .76) across all RPP, and the overall mean passages did not differ from zero (P greater than .34); similar results were observed for other VFA. These observations indicate that essentially all RPP is removed prior to entering the small intestine. Additionally, net propionate disappearance across the small intestine was undetectable and likely biologically irrelevant. Therefore, VFA absorption does not appear to be a limiting biological process in the beef steer.

This study was conducted to determine the effect of daily recombinant porcine somatotropin (rpST) injection (0 or 120 micrograms/kg BW) and dietary CP level of the feed (14 or 26% CP) on pancreatic characteristics of growing pigs. Daily injection of rpST did not affect pancreatic weight (P = .885) but did decrease pancreatic amylase content (P = .005). The ratios of amylase:protein and amylase:trypsin were also lowered by daily rpST injection (P = .002 and P = .0002, respectively). There were protein x rpST and protein x rpST x sex interactions for the ratio of amylase:chymotrypsin. The CP content of the diet had a greater effect than the injection of rpST on pancreatic characteristics. Pigs consuming the 26% CP diet had significantly higher pancreatic weight (P = .003) and greater total pancreatic chymotrypsin (P = .006) than pigs consuming the 14% CP diet. The ratios of trypsin and chymotrypsin to DNA were also higher in pigs fed the 26% CP diet (P = .007 and P = .005, respectively). These responses were not influenced by sex. Recombinant porcine somatotropin seemed to have a slight effect on porcine pancreatic characteristics; however, dietary protein had a greater effect on pancreatic characteristics in market-weight hogs.

total.desirable. Malic and citric acid concentrations were different between bluestem (Andropogon caucásica) and switchgrass (Panicum virigatum) and two genotypes of tall fescue (Festuca arundinacea). The method has been applied to a more complete genotypical study of tall fescue to be reported elsewhere. ACKNOWLEDGMENTThe technical assistance of Matt Press and the supply of tall fescue samples from Kay Asay, Department of Agronomy, are gratefully acknowledged. LITERATURE CITEDBergmeyer, . V., Ed., "Methods of enzymatic analysis," Williamson, D. H., trans., Verlag-Chemie. Gmbt, Weinheim/