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Glucose absorption via the sodium glucose-linked transporter (SGLT)-I, decreases the glucose concentration in the ruminant forestomach and may ameliorate or prevent ruminal lactic acidosis. Because acidotic ruminants show increased sympathetic activity, the possibility of adrenergic modulation of SGLT-1 was investigated. Glucose uptake into ovine ruminal epithelia was measured in Ussing chambers after the addition of 200 [micro]mol/L [sup.14]4C-labeled glucose to the mucosal solution. Glucose uptake decreased (P < 0.05) by >50% in comparison with control after mucosal addition of the SGLT-1 inhibitor, phlorizin (100/[micro]mol/L). Serosal preincubation with 100 [micro]mol/L epinephrine increased (P < 0.05) the phlorizin-sensitive glucose uptake in the absence and presence of indomethacin (10 [micro]mol/L). The effect of epinephrine was simulated by [beta]-(100 [micro]mol/L isoproterenol) and [beta][sup.2]-receptor agonists (10 [micro]mol/L terbutaline), as well as by direct stimulation of adenylyl cyclase (10 [micro]mol/L forskolin). The serosal addition of methoxamine, clonidine, dobutamine or,BRL 37344 had no effect. Inhibition of protein kinase A with 2 [micro]mol/L H 89 completely abolished the stimulation of glucose uptake by epinephrine. We conclude that ruminal SGLT-1 can be stimulated via [beta][sub.2]-dependent generation of cyclic adenosine monophosphate. KEY WORDS: * glucose absorption * cAMP * epinephrine * rumen * sheep

Results obtained during the past decade indicate clearly that protozoa are actively involved in the degradation of dietary and microbial proteins in the rumen. Because of the great ability of protozoa to ingest the particulate matter suspended in the rumen, protozoa are more active in degrading insoluble than soluble proteins. This indicates that studies carried out using lysed and sonicated protozoa are not appropriate for quantifying the actual contribution of protozoa to protein degradation in the rumen. In vivo trials have confirmed that duodenal flow of both undegraded dietary protein plus bacterial protein generally is increased by defaunation. The decrease in ruminal ammonia concentration consistently observed after defaunation accounts for the lower urinary nitrogen (N) excretion found in defaunated animals, whereas the increase in fecal N excretion in the same animals probably results from a shift of plant cell wall digestion from the rumen to the large intestine. Total N excretion is not altered significantly by defaunation. A summary of literature data indicates there are contradictory effects of defaunation on ruminant performance. This implies that animal response to defaunation may depend on the specific nutrient-limiting performance on the one hand and on the modifications of digestion and metabolism resulting from defaunation on the other. Different methods are proposed to either eliminate or decrease the numbers of ruminal protozoa or to alter their makeup. However, none of these approaches has been tested under practical feeding conditions. J. Nutr. 126: 1335S-1346S, 1996. INDEXING KEY WORDS: rumen, nitrogen, digestion, metabolism, protozoa

Microbial protein supply to the duodenum should be maximized for efficient use of feed protein and energy. High producing ruminants often are fed significant concentrations of cereal grains and fat in their diets. Increasing starch in the diet decreases ruminal pH, which often decreases extent of ruminal fiber digestion and also may decrease efficiency of microbial protein synthesis because of energy-spilling reactions. In contrast, higher grain feeding increased efficiency of microbial protein synthesis in some studies because ruminal passage rate was increased. Ruminal degradation of carbohydrates and protein must be synchronized for optimal microbial efficiency, but the microbes appear to withstand transient periods of asynchronous nutrient supply in many cases. Protozoa extensively prey upon bacteria, and a higher proportion of protozoa than bacteria lyse within the rumen, recycling significant amounts of protein. Feeding moderate amounts of unsaturated fat appears to reduce, especially on relatively low forage diets, protozoal numbers and the extent of intraruminal recycling. Indirect and direct calculations have been derived from models to estimate microbial protein transactions within the rumen; however, models need further definition and more detailed inputs from published literature to further their predictive ability. J. Nutr. 126: 1347S-1354S, 1996. INDEXING KEY WORDS: rumen, nitrogen, microbial protein synthesis, intraruminal recycling, rumen models

In vivo and in vitro studies of sheep rumen were made in the preweaning period, or 42 days, to determine its development pattern. Observations show that the rumen, which is about 80% of stomach mass, undergoes great physical and metabolic changes in this period. Its wet weight grows linearly with body weight from birth and three times faster from day 28 to 42. By day 14, rumen cells undergo a glucose oxidation rate to CO2 1.8 times faster than those of mature cells. By day four, the cells go into peak butyrate oxidation to CO2. By day 42, butyrate overtakes glucose oxidation by a 10-fold rate increase.