Studies of weaned lambs before, during and after a period of weight loss. I. Energy and nitrogen utilization

Abstract

Lambs were given a balanced diet immediately after weaning at 6 weeks and grown from 15 to 25 kg on a high level of feeding. They were then underfed for 21 weeks, which caused weight to return to 17 kg, and finally allowed to regain weight on ad libitum feeding. Brief periods of 'maintenance' feeding were interposed in each phase. Nitrogen and energy balances were obtained for successive weeks by measuring food intake and all losses. There was general agreement between these results summed for each phase of the experiment and data obtained from a parallel slaughter trial.

Metabolizable energy was a constant 56% of gross energy or 11.3 MJ/kg dry matter. Estimated energy requirement for maintenance was depressed by 28% after a few weeks of undernutrition, but efficiency of utilizing additional energy was also lowered, cancelling the potential benefit for compensation. There was no difference in efficiency between normal and compensatory growth. Protein contributed 25–40% (varying inversely with body weight) of energy balance during both normal growth and regain but only 10% during prolonged weight loss. There was some evidence of improved nitrogen economy in the first month of compensation.