1.Two experiments were conducted to assess the nutritional value of lupin (Lupinus albus)-seed meal for growing pigs. In the first, the availability of lysine was assessed using slope-ratio analysis. In the second, the effects of autoclaving lupin seeds and formulating the diets on the basis of estimated digestible or net energy were assessed.
2. In the first experiment, the availability of lysine in three samples of lupin-seed meal was compared with that in meat-and-bone meal and soya-bean meal. Availability of lysine in the five protein concentrates, using food conversion efficiency on a carcass basis as the criterion of response, was (proportion of total): lupin-seed meal no. 1 0.44, no. 2 0.57, no. 3 0.53, meat-and-bone meal 0.42, soya-bean meal 0.80.
3. Availability estimates, based on protein deposited:food intake, were: lupin-seed meal no. 1 0.82, no. 2 0.73, no. 3 0.70, meat-and-bone meal 0.27, soya-bean meal 0.77. These estimates had higher standard deviations than those based on carcass response.
4. Regressing the measures of response v. lysine intake resulted in estimates of availability similar to, or higher than, the slope-ratio analysis but was associated with greater statistical invalidity and higher standard deviations.
5. The proportion of energy retained in the carcasses was unaffected by the inclusion levels of lysine or soya-bean meal. Energy retention was depressed (P < 0.05) with the three lupin-seed meals and the meat-and-bone meal.
6. In the second experiment, the response of pigs given a diet containing lupin-seed meal was inferior, on a carcass basis (P < 0.05), to that of pigs given a diet containing soya-bean meal formulated to similar total lysine and digestible energy contents.
7. The addition of soya-bean oil to the diet containing lupin-seed meal, to equalize the estimated net energy of the diet to that of the diet containing soya-bean meal, depressed protein deposition (P < 0.05) and increased fat deposition (P < 0.05), indicating that energy was not limiting the growth of pigs given the lupin-seed-meal diet.
8. Autoclaving the lupin-seed at 121°for 5 min had no effect on the growth of pigs, indicating that the low availability of lysine was not due to the presence of heat-labile anti-nutritional factors.