The effect of a reduction in food intake during late pregnancy on nitrogen metabolism in ewes

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Abstract
Twelve Finnish Landrace × Dorset Horn ewes with a mean litter size of 1·92 and a mean body weight of 75±3 kg were individually penned from 80 days of gestation to parturition and offered a diet with a metabolizable energy (ME) and crude protein content in the dry matter of 9·7 MJ/kg and 11·4% respectively. At 120 days of gestation daily ME intake was abruptly reduced from a mean of 0·48 to 0·25 MJ/kg W0·75for a period of 10 days.The observed increase in the plasma concentration of urea due to the reduction in food intake was better correlated with lamb birth weight (r= 0·87) than was the increase in plasma free fatty acid concentration (r= 0·53) or the decrease in plasma glucose concentration (r= 0·76). Mean daily nitrogen balance decreased from a mean of 5·6 g before food restriction to – 1·8 g after food restriction. Although the effect was not significant, single bearing ewes excreted more total and urea nitrogen in the urine than multiple bearing ewes before food restriction. During food restriction the trend was reversed. The change in urea nitrogen excretion (Y, g/day) that resulted from the reduction in food intake was correlated (r= 0·73,P< 0·01) with lamb birth weight (X, kg); the relationship wasY= 0·54(±0·16)X – 3·48. It was estimated that the daily loss of nitrogen from the maternal body during the period of food restriction was approximately 80% of published values for the urinary nitrogen excretion of fasting non-pregnant sheep.