Studies on protein utilization by ewes during lactation

Abstract

SUMMARY: A total of 64 Border Leicester × Greyface ewes were offered eight diets comprising four levels of digestible crude protein and two levels of metabolizable energy (ME) intake during gestation. After parturition the ewes on each gestation treatment were offered a high or low level of ME intake at a constant level of crude protein intake. Nitrogen balances were carried out on all ewes during weeks three and four of lactation.Digestibility coefficients and output of nitrogen in the milk measured during the lactation balance periods were not significantly affected by the gestation treatments. Body nitrogen balance during lactation was significantly affected by the level of protein offered during gestation.Empirical equations relating digestible crude protein intake and ME intake to milk nitrogen production and body nitrogen balance indicated that a digestible crude protein intake of 7·9 g/kg W^0·75 per day and a ME intake of 220 kcals/kg W^0·75 per day resulted in the production of 0·70 g milk nitrogen per kg W^0·75 or approximately 100 g of milk per kg W^0·75. The corresponding level of body nitrogen retention was 0·162 g/kg W^0·75 per day and showed no consistent trend due to level of protein intake during gestation.