Nitrogen utilization and digestibility by growing steers and goats of diets that contain monensin and low crude protein.

Two digestion and metabolism experiments were conducted to determine effects of monensin in low-protein diets. Monensin supplementation (27 mg/kg of diet dry matter) of steers (303 kg) fed 8.7% crude protein increased (P less than .01) apparent N digestibility and N retention and decreased (P less than .01) percentage of N apparently absorbed lost in urine. Apparent digestibilities of dry matter, gross energy and acid detergent lignin were increased (P less than .05). Digestibilities of neutral detergent and acid detergent fibers were not affected by monensin. In growing wether goats (15 kg) fed 8.5% crude protein, monensin (23 mg/kg of diet dry matter) improved (P less than .01) apparent N digestibility and apparent N absorption. However, urinary N excretion also increased (P less than .05), resulting in no difference in N retention. Monensin did not affect digestibilities of dry matter or gross energy. Efficiency of feed conversion and average daily gain were improved with monensin supplementation of growing goats fed a low-protein, high-roughage diet. Monensin resulted in typical shift of acetate-to-propionate ratio in both experiments. Results suggest that improved N utilization may account for some benefits of feeding monensin.

Isolation-perfusion of ovine hind limbs. IV. Effects of level of activity on amino acid and glucose metabolism.

Twenty-one wether lambs averaging 30.0 kg were utilized in a study to determine the influence of level of muscular activity (via electrical stimulation) on metabolism of amino acids and glucose of isolated-perfused hind limbs. Treatments consisted of: (1) control, (2) low electrical stimulation and (3) high electrical stimulation. Mean perfusion flow rate was unaffected by treatment or time of perfusion. Perfusion pressure and hematocrit were increased (P less than .05) by stimulation. Glucose levels decreased from a pretreatment average of 44.7 to 41.3, 26.8 and 20.0 mg/dl for treatments 1 to 3, respectively. Lactic acid levels increased from the pretreatment mean of 37.7 to 46.7, 63.8 and 69.4 mg/dl, respectively. Plasma-free fatty acids were utilized from the perfusate at .84, .76 and .68 meq X liter-1 X min-1, respectively. Perfusate urea N levels were unaffected by treatment or time of sampling, but perfusate ammonia levels increased in all treatments (ammonia levels for treatments 1 to 3 increased by .50, 1.09 and 1.47 mg/dl, respectively). Perfusate amino acid changes suggested a flux of some amino acids from muscle to perfusate due to electrical stimulation, but perfusate branched chain amino acid concentrations decreased in all treatment groups. Fifty microcuries of 14C-lysine were included in the initial perfusate. Total perfusate radioactivity in all treatments declined with time, reflective of lysine uptake by the muscle. Total perfusate lysine concentration changed less markedly, suggesting that muscle is contributing to maintenance of plasma amino acid levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetate and propionate production in the cecum and proximal colon of lambs.

A modified single-injection isotope dilution technique measured acetate and propionate production rates in the cecum and proximal colon of 14 lambs fed a forage (hay) or high corn (concentrate) diet. The modified isotope dilution appeared to have merit. Volatile fatty acid pool sizes were stable and apparently absorption of fermentation products occurred to prevent end product inhibition. Propionate pool sizes were greater (P less than .01) while acetate pool sizes were not significantly greater when lambs received the concentrate diet. Apparent acetate production was higher (P less than .05) in lambs fed the concentrate diet than in forage-fed lambs (239.4 vs 189.5 mmol/d, respectively). Apparent propionate production was also greater (P less than .01) when lambs were fed the concentrate diet rather than the forage diet (431.4 vs 180.7 mmol/d, respectively). These results indicate that acetate and propionate produced in the cecum and proximal colon may be a considerable source of energy and glucose precursors for the growing lamb.

Carbohydrate fermentation in the large intestine of lambs.

In one of two experiments, six 4-mo-old wethers fitted with ileal and cecal cannulas were fed three levels of concentrate (0, 40 or 80% corn) with forage in a replicated 3 X 3 Latin square design. Chromic oxide was fed as a marker. Quantities of starch recovered at the ileum and digested in the large intestine increased (P less than .05) with increased starch intake. Quantities of acid detergent fiber (ADF) recovered at the ileum increased with increased ADF intake; however; ADF digestion (grams) in the large intestine was highest (P less than .05) when the 80% corn diet was fed. Cecal total VFA concentrations, butyrate molar proportions and lactic acid concentrations were highest (P less than .05), and cecal acetate to propionate (C2:C3) ratios and pH values were lowest, in lambs fed 80% corn. In Exp. 2, 14 wethers (4-mo-old) were fed a forage (alfalfa hay) or a concentrate (80% corn) diet containing chromic oxide as a marker. Digesta grab samples were obtained by surgical procedure. The amounts of starch recovered at the abomasum and ileum and the amounts digested in the rumen, small intestine and large intestine were greater (P less than .05) when lambs were fed the concentrate. Large intestinal total VFA concentrations and butyrate molar proportions were higher (P less than .01) when the concentrate diet was fed; pH values were lower (P less than .01). Lambs fed the concentrate diet had lower (P less than .01) large intestinal and ruminal C2:C3 ratios of VFA.