Some effects of nutrition and heat stress on urea excretion by pregnant sheep

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Abstract
Renal clearance of urea and creatinine were measured at mating time and near lambing time in three groups of seven sheep, the groups being given differing amounts of food. On each occasion the measurements were made at normal ambient temperature (20°C) and in a hot environment (35°). The ewes on the lowest feeding level were severely undernourished in late pregnancy. Urine flow and the composition of blood and urine were quite variable, with standard deviations equal to 10–20% of mean values. Renal clearance of urea was greater at the highest feeding level (29–41 ml/min) than at the other levels (19–26 ml/min). Heat stress caused it to increase by 6–12 ml/min at mating time but had no effect in advanced pregnancy. Actual excretion of urea varied similarly. Urea clearance was a relatively constant fraction of creatinine clearance (40–50%).– It is concluded that apparent nitrogen economy or urea conservation by the pregnant ewe subjected to heat stress or caloric undernutrition is not evident at the renal level. It is suggested rather, that nitrogenous moieties of oxidized protein may be re-utilized.

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