Interactions between dietary carbohydrate and nitrogen and digestion in sheep

Abstract

Rumen fermentation, duodenal digesta flow and N balance were studied in three sheep fed diets which contained urea or fishmeal as nitrogen supplement and either barley straw, barley + corn starch or molassed wheat straw (60% molasses) as carbohydrate source.The molar composition of rumen volatile fatty acids (VFA) with straw diets was high in acetate (64-68%), with barley diets high in propionate (32-36%) and with molasses diets high in butyrate (28-34%). Rumen ammonia concentrations (RAC) were low and constant with fishmeal diets (< 10 nun) but varied with carbohydrate source with urea diets. RAC was very high (24 nun) after feeding molasses + urea.With barley and molasses diets 73-75 % of digestible dry matter (DDM) was digested in the stomach, but only 54-59 % with ground and pelleted straw diets. For all diets less N passed the duodenum than was eaten. The lowest daily duodenal N passage was with molasses + urea. Daily urinary N output was highest (P < 0-01) for this diet and nitrogen balance lowest.Daily intakes of amino acids differed widely between diets but differences in duodenal passage were not so great. Molasses + urea provided the lowest values for daily duodenal amino acid flow. The amino acid content of duodenal N (min amino acid/16 g N) was relatively constant despite broad variation between diets. Digesta alanine and valine (mM/16 g N) were higher for barley than for straw diets (P < 0-05). Digesta methionine (mi/16 g N) was lower for fishmeal than for urea diets (P < 0-01).Very little sucrose reached the duodenum with any diet. It was concluded that the form of energy-yielding nutrient inuflenced duodenal N flow by affecting ammonia-N capture in the rumen, but that the amino acid content of duodenal N was little affected. The interaction between molasses and urea was not beneficial to efficient use of urea-N in this work when molasses was the major carbohydrate component of the diet.

Effect of different levels of Quebracho tannin on nitrogen utilization and growth performance of Najdi sheep fed alfalfa (Medicago sativa) hay as a sole diet

“…In spite of the reduction of MNS in QT3, alfalfa hay treated by QT at the level of 1 and 2% had slightly enhanced MNS by about 3% in QT1 ( P > 0.05) and 6% in QT2 ( P < 0.05) as compared to that of QT0, respectively. Oldham et al. (1977) found that the efficient utilization of degraded N requires that the energy from the fermentation of dietary OM must be supplied at a rate which matches the synthetic abilities of the rumen microbes.…”

“…In spite of the reduction of MNS in QT3, alfalfa hay treated by QT at the level of 1 and 2% had slightly enhanced MNS by about 3% in QT1 (P > 0.05) and 6% in QT2 (P < 0.05) as compared to that of QT0, respectively. Oldham et al (1977) found that the efficient utilization of degraded N requires that the energy from the fermentation of dietary OM must be supplied at a rate which matches the synthetic abilities of the rumen microbes. The slight improvement of MNS in QT1 and QT2 might be due to a greater microbial synthesis through the increment of energy supply as a result of increasing fiber digestion (Table 2) and the reduction of excess N release in the rumen (Table 1).…”

Food intake and diet selection in sheep: the effect of manipulating the rates of digestion of carbohydrates and protein of the foods offered as a choice

“…The avoidance of excess eRDP could protect them from an excessive load of NH3. This risk of NH3 escaping into the peripheral circulation is lower when the carbohydrate source of the foods is a rapidly fermentable one, rather than a slowly fermentable one, since in the presence of the former, rumen NH3 resulting from N degradation can be taken up at a faster rate by the rumen microbes (Oldham et al 1977;Sinclair et al 1993Sinclair et al , 1995. The fact that the diet selections by R f l H and SJSH animals did not result in a certain, similar level of rumen NH3-N concentration, should not be taken as contradicting the above suggestions.…”

THE EFFECT OF DIET, INTRARUMINAL pH AND OSMOLARITY ON SODIUM, CHLORIDE AND MAGNESIUM ABSORPTION FROM THE TEMPORARILY ISOLATED AND WASHED RETICULO‐RUMEN OF SHEEP

“…Intake of high levels of easily fermentable carbohydrates leads to an alteration of microbial activity and composition in the rumen contents. In particular, production rate, molar ratio and concentration of short-chain fatty acids are influenced by the diet (Sutton, 1968(Sutton, , 1969Oldham, Buttery, Swan & Lewis, 1977;Baldwin & Allison, 1983).…”