Feed utilization, energy expenditure and nitrogen metabolism in working female buffaloes (Bubalus bubalis)

Abstract

Four 36-months-old female buffaloes, with a mean liveweight of 345 kg, were used in a study designed to estimate the effect of work (3 h/day) on feed utilization, energy expenditure and nitrogen metabolism. The animals were studied under ambient temperatures and relative humidities ranging from 25.3 to 32.5'C and 45 to 82% respectively, and were fed rice straw (0.8% nitrogen) ad libitum, supplemented with cottonseed meal at 500 g head-1 day-1 to result in a dietary nitrogen content of 1.15%. Work did not affect the digestibility of the feed but tended to reduce (P=0.054) ad libitum intake of its organic matter. Rectal temperatures and respiration rates were increased during work from 37.7 to a peak of 40.8¦C and from 40 to a peak of 130 counts/min respectively. The ratio of working : resting metabolic rate, as calculated from CO2 entry rates, was approximately 2.6. Estimates of energy expenditures from CO2 entry rates showed increases in the working animal by 2.3 to 2.7 times the resting values. Nitrogen balance was reduced in the working animal owing to increased catabolism of amino acids and the resultant increased excretion of urea via the urine. Urea entry rate was increased in the working animal, but the proportion of this that was estimated to be transferred to the digestive tract was not different from that in the non-working animal, although the amount transferred was greater in the working animal. It is suggested that increased muscular activity in the working animal would tend to reduce ad libitum intake of organic matter of a roughage such as rice straw, but could increase digestibility of organic matter possibly through reduction in the rate of passage of digesta and/or through increased amount of urea transferred to the rumen containing lower than an optimal level of ammonia. The increased catabolism of amino acids associated with increased muscular activity is likely to result in a reduced nitrogen balance due to the likely increased urea excretion via the urine. It is also suggested that CO2 entry rate could offer a reasonable estimate of energy expenditure in the resting and the working animal.