Influence of continuous intravenous lysine and methionine infusion on N balance in growing sheep fed diets that differ in ruminai degradable protein

Abstract

The effect of continuously infused lysine and methionine with glucose on nitrogen retention in young wethers (average liveweight 31.3 kg) fed diets with different protein degradation in the rumen in two 4 × 4 Latin squares design was investigated. The wethers of a particular Latin square were fed at a level of 1.2-times their maintenance energy requirement either with a diet based on ground barley and urea (B+U), with high degradable intake protein (HDIP) or a diet based on cracked maize and maize gluten meal (M+MGM), with high undegradable intake protein (HUIP). The wethers of each Latin square were continuously infused (jugular) with control solution (Control), or with L-lysine (Lys), DL-methionine (Met) or their combination (Lys+Met). Infusion rates for the above mentioned amino acids were 3.0, 1.5 and 3.0 g+1.5 g lamb-1 day-1, respectively, estimated to be about 50% of maintenance. Glycine was added to the infusion solutions to equalise the total N infused. Glucose (12 g kg B W0.75d-1) was also supplemented in the infusion solution to minimise endogenous gluconeogenesis. The average digestibility coefficients of DM and N were 73.6 and 60.2% for the B+U and 78.4 and 63.5% for the M+MGM diets, respectively, and were not affected by infusion treatments. The continuous infusions of Lys, Met and Lys+Met improved N retention, irrespective of the diet, by 30, 34 and 36%, respectively. The effect, however, depended on the diet. When the diet contained the HDIP (about 80%), based on barley and urea, N retention increased by 13, 20 and 29%, respectively with Lys, Met and Lys+Met infusions. Feeding a HUIP diet (about 60%), based on maize and maize gluten meal, increased N balance by 43, 44 and 40%, respectively with Lys, Met and Lys+Met infusions.