A study of protein utilization by weaned lambs

Abstract

SUMMARYFifty weaned store lambs approximately 7-month-old were used in an experiment designed to assess their protein requirements and utilization. At the beginning of the experiment a random sample of 10 animals were slaughtered and their loin joints analysed. The remaining 40 were allocated at random to four dietary treatments (T1, T2, T3, T4) comprising four crude protein intakes at a constant energy intake. The experiment was divided into two periods. During period 1 (48 days) the dietary crude protein intakes were 58 (T1), 111 (T2), 170 (T3), and 198 (T4) g/day with a mean digestible organic matter intake (DOMI) of 578 g/day. During period 2 (55 days) the corresponding crude protein intakes were 89, 157, 215, 251 and the DOMI was 678 g/day.Digestibility and nitrogen balance trials were carried out on two animals from each treatment in period 1 and on six animals on each treatment in period 2. At slaughter the loin joints from five animals on each dietary treatment were chemically analysed.The only significant effect on live-weight gain of varying protein intake was a lower gain on the lowest protein intake (T1) in period 1. It was estimated that the optimum ratio of digestible protein intake (g) to digestible energy intake (meals) for live-weight gain in period 1 was approximately 30 : 1 and in period 2 approximately 21 : 1. There was a significant increase in killing-out percentage with increasing crude protein intake. The digestibility of dry matter and nitrogen increased with increasing crude protein intake. There was a significant quadratic relationship between the apparently digested nitrogen intake in g/day (X) and nitrogen retained in g/day (Y). The regression equation wasY= −0·008X2+ 0·537X+ 0·682Liver copper levels decreased with increasing crude protein con-centration in the diets.

Influences of diet and body condition on the nitrogen utilization in the cow

“…The nature of the relation existing between, on the one hand, nitrogen intake or digestible nitrogen and, on the other hand, urinary nitrogen or nitrogen balance has been investigated previously. It was expressed as an equation of the type Y = a + bX + cX 2 (Elliott & Topps, 1964;Robinson & Forbes, 1970;Uhlemann & Poppe, 1970) or of the type Y = a + bX (Orskov & Fraser, 1969;Walker & Cook, 1967;Wallace, Knox & Hyder, 1970). We subjected our results to linearity and curvilinearity tests, and we found that the relations were linear (equations (1)-W).…”

The effect of pattern of protein intake and level of energy intake on the performance and nitrogen utilization of the ewe

“…Wool growth rates. These were based on mid-side clips and were carried out as described by Robinson & Forbes (1970).…”