Influence of sucrose supplementation on nitrogen kinetics and energy metabolism in sheep fed with lucerne hay cubes

Abstract

SummaryThe effects of sucrose supplementation on nitrogen kinetics and energy metabolism were examined in sheep fed lucerne hay cubes using a15N isotope dilution method and balance and respiration trials in Tsukuba, Japan in 1988. Sheep were fed lucerne hay cubes (1183 g DM/day), with or without 204 g/day sucrose, at 2 h intervals from continuous feeders. Supplementation with sucrose decreased urinary N excretion (P< 0·01), resulting in an increase in N retention from – 1·1 to + 2·0 g N/day (P< 0·01). Supplementation with sucrose resulted in no change in faeces and methane energy, a decrease in urinary energy (P< 0·01) and an increase in heat production and energy balance (P< 0·01). Sucrose supplementation also resulted in lower rumen ammonia (P< 0·05) and plasma urea concentrations (P< 0·05) and reduced urinary urea excretion (P< 0·01). The fermentation of sucrose in the rumen resulted in a decrease in rumen pH (P< 0·01) and in the acetate: propionate ratio (P< 0·05). Sucrose supplementation increased the proportion of urea transferred to the rumen (P< 0·05), non-ammonia N (NAN) concentration in the rumen (P< 0·001) and NAN flow from the rumen to the lower digestive tract (P< 0·001). Urinary allantoin excretion rate increased with sucrose supplementation (P< 0·05). The plasma glucose concentration was unchanged but plasma insulin concentration was increased with sucrose supplementation (P< 0·05). The influence of energy-rich supplements, such as sucrose, on N kinetics and the mechanism of the increase in N retention with sucrose supplementation are discussed.