The nutritive value of lupin-seed and dehulled lupin-seed meals as protein sources for growing pigs as evaluated by different techniques

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Four experiments were conducted to determine the effect of dehulling lupin-seed meal ( Lupinus angustifolius cv. ‘Gungurru’) on its nutritional value, relative to soya-bean meal, for growing pigs. In addition, a number of different techniques for assessing nutritional quality were compared—ileal digestibility by cannulation and slaughter techniques, total tract digestibility by total collection and partial collection using a marker and amino acid utilisation by nitrogen balance and slaughter techniques. In all experiments, the meals were fed as the sole protein concentrate in sugar-based diets. Compared with lupin-seed meal, the dehulled lupin-seed meal (kernel) had a higher (g kg −1) crude protein (405 vs. 311), lysine (20 vs. 16), ileal digestibility of amino acids (lysine, 0.88 vs. 0.82) and digestible energy content (16.3 MJ kg −1 vs. 13.1 MJ kg −1) but lower crude fibre (51 g kg −1 vs. 172 g kg −1). In the growth experiment, diets were formulated to 0.36 g ileal digestible lysine MJ −1 digestible energy. Six diets were compared: lupin-seed meal, kernel, soya-bean meal, soya-bean meal plus lupin hulls, and lupin-seed meal and soya-bean meal supplemented with lysine (to confirm that lysine was first limiting in the first four diets). Diets were given at three times energy requirements for maintenance to growing pigs over the 20–45 kg growth phase. Growth response of the pigs given the lupin-seed meal diet was greater than those given kernel or soya-bean meal ( P < 0.05). The addition of hulls to the soya-bean meal diet improved ( P < 0.05) growth response and there was no significant difference between the lupin-seed meal or soya-bean meal plus hulls diet ( P > 0.05). Protein deposition rates were similar to the growth responses. Lysine retention as a proportion of ileal digestible intake was: lupin-seed meal 0.70, kernel 0.68, soya-bean meal 0.64, soya-bean meal plus hulls 0.69. Ileal digestibilities were similar with the two techniques although the slaughter technique was unsuitable with the highly digestible soya-bean-sugar diets. Lysine retention was higher with the nitrogen balance technique, relative to the slaughter technique. Overall the results indicate that L. angustifolius cv. ‘Gungurru’ lupin-seed meal is of high nutritional value, and that dehulling the meal lowered the nutritional value for growing pigs.