The effect of a hindgut fermentation on urea metabolism in sheep nourished by intragastric infusion

Abstract

SUMMARYFour female sheep nourished wholly by infusions of volatile fatty acids, buffer and minerals into the rumen and casein into the abomasum were given, in addition, infusions of fermentable carbohydrates into the terminal ileum. The ileal infusions consisted of (1) water alone, (2) 25 g starch + 50 g cellulose, and (3) 50 g starch + 50 g cellulose. Measurement of nutrient digestibility and nitrogen retention were made over 5 days and the kinetics of urea metabolism were measured over 24 h by means of a single injection of ['4C]urea. Endogenous urinary nitrogen excretion was measured over a subsequent 5 days when casein was omitted from the infusion mixtures. Increases in hindgut fermentation resulted in a significant increase in faecal nitrogen excretion (P < 0 01) and a corresponding reduction in urinary urea nitrogen excretion (P < 0 05). The ileal infusions did not significantly affect urea irreversible loss rate or urea pool size and were also without effect on plasma urea or rumen ammonia concentrations. Urea degradation in the gastrointestinal tract increased by about 2 g/day in progressing from lowest to highest level of hindgut infusion but differences between treatments were not statistically significant. Endogenous urinary nitrogen excretion was not affected by hindgut fermentation and averaged 206 mg N/(kg0 75 day) over the three treatment groups. Faecal nitrogen excretion however increased progressively with increase in ileal infusions (P < 0 05) and was similar to that seen when nitrogen input was adequate. It is concluded that changes in hindgut fermentation can alter the partition of nitrogen excretion between faeces and urine but the quantities involved are small relative to the total exchange of urea across the digestive tract. The rumen appears to be an important site of urea degradation even when microbial fermentation is absent.

Urea degradation in sheep nourished by intragastric infusion: effects of level and nature of energy inputs

“…The linear relationship between urea degradation and ILR in this experiment (Table 5) was almost identical to that reported in our previous work (Oncuer et al 1990 (Table 3). Indeed, it is interesting to note that there are remarkably few reports in the literature in which a measured increase in urea degradation has been shown unequivocally to result in a net gain of N to the host animals (Norton et al 1982 b;Whitelaw et al 1990).…”

“…The methods for the estimation of urea in urine and plasma, total N in faeces, urine and casein and osmotic pressure (OP), VFA proportions, NH3 and urease in rumen fluid were as described by Whitelaw et al (1990) and Oncuer et al (1990). Plasma glucose concentrations were measured by the method of Trinder (1969) and the concentrations of total purine bases in urine were assayed by the method of Chen, Mathieson, Hovell & Reeds (1990b).…”

“…Urea degradation in the GI tract did not differ between the two dietary situations and we have therefore used the sheep nourished in this way as a model for the study of dietary factors thought to be associated with the process of urea recycling (Oncuer, Milne & Whitelaw, 1990). A prime advantage of this method of feeding is that all nutrient inputs can be precisely controlled and can be varied independently of each other when required.…”

Effect of fat supplementation on nitrogen utilisation of lambs and nitrogen emission from their manure

“…Apparently, the hindgut of ruminants is able to compensate to a large extent for a reduced ruminal digestion. An increased microbial protein synthesis in the hindgut, although not contributing to the metabolic protein supply, is associated with correspondingly lower urinary N losses as well (Oncuer et al, 1990). Kü lling et al (2002), comparing ruminally active dietary lauric acid with presumed inactive stearic acid noted higher faecal fibre contents at unchanged urine N proportion of manure N and no effects on gaseous N losses from manure during storage.…”

The effect of a rumen microbial fermentation on urea and nitrogen metabolism of sheep nourished by intragastric infusion

“…1 to identify the sites of NH3 absorption and it is not possible from the information available to validate the sizes of the urea N subpools identified; indeed, it is unlikely that these exist as separate entities. Oncuer et al (1990) and Whitelaw & Milne (1991) have discussed the possible sites of urea and NH3 transfer and absorption in the gut of animals nourished by intragastric infusion and have concluded that the rumen is probably the major site for this activity both in the presence and the absence of a rumen microbial population. We see no reason to depart from this conclusion at the present time.…”