An experiment was conducted to determine the utilization of ileal digestible threonine by growing pigs. Three threonine-deficient diets (0.22 g ileal digestible threonine/MJ digestible energy (DE)) were formulated using cottonseed meal, meat-and-bone meal and soya-bean meal respectively, as the only source of threonine in the diet. An additional three diets were formulated with supplements of threonine to confirm that threonine was limiting in the first three diets. The growth performance and retention of threonine by pigs given the six diets over the 20–45 kg growth phase was then determined. Growth rates (g/d) of the pigs given the three diets formulated to 0.22 g ileal digestible threonine/MJ DE were significantly different (P < 0.001): cottonseed meal 417, meat-and-bone meal 452, soya-bean meal 524 (sed 13.6). The response of pigs to the addition of threonine confirmed that threonine was limiting in these diets. Crude protein (nitrogen x 6.25) deposited by the pigs (g/d) was significantly higher (P < 0.001) for those given soya-bean meal (75), relative to meat-and-bone meal (62) and cottonseed meal (47) (sed 3.3). The proportion of ileal digestible threonine retained by pigs given the three protein concentrates was: cottonseed meal 0.44, meat-and-bone meal 0.59, soya-bean meal 0.64 (sed 0.024). These results indicate that values for the ileal digestibility of threonine in protein concentrates are unsuitable in dietary formulations as the assay does not reflect the proportion of threonine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the threonine is absorbed in a form(s) that is (are) inefficiently utilized.

One hundred and eight New Zealand × Californian growing rabbits (nine per diet) were used to determine the nutritive value (digestible energy (DE), digestible protein (DCP) and digestible acid-detergent fibre (DADF)) of five protein concentrates. In assay 1, the effect of the type of basal diet (BD) (7·6 or 10·0 MJ DE per kg dry matter (DM) for BD1 and BD2 respectively) and the substitution level (150, 300 and 450 g/kg) on nutritive value of soya-bean meal was studied. According to the results of assay 1, one basal diet (BD2) and one substitution level (300 g/kg for sunflower 380, gluten meal and extruded soya-bean meal or 500 g/kg for sunflower 320) were selected in assay 2 to determine their nutritive value.

The effect of the basal diet and the substitution level on the nutritive value of soya-bean meal was evident only for the values calculated from BD1 and the lowest level of inclusion. The data obtained by difference at the highest level of inclusion and by extrapolating the linear equations were very similar (16·32 v. 16·35 MJ DE and 387·62 v. 388.58 g DCP per kg DM for BD2), but the standard errors were lower (0·52 v. 0·72 for DE and 6.76 v. 8.95 for DCP) in the former. The DE values obtained for sunflower meal 320 and 380, extruded soya-bean and gluten meal were 10·29, 14·37, 18·58 and 20·57 MJ/kg DM respectively; protein digestibilities were high (with coefficients from 0·80 to 0·90) except in the case of sunflower-320 (0·73). A stepwise regression analysis was made to predict the nutritive value from chemical composition including values from literature. For prediction of DE, the variables selected were: crude fibre, ether extract and ash, obtaining a determination coefficient of 0·935. The protein digestibility was independent of variables employed.

Two experiments were conducted to determine the utilization of ileal digestible lysine by pigs. In the first, the apparent ileal digestibility of amino acids in cottonseed meal, meat-and-bone meal and soya-bean meal was determined in pigs fitted with‘T'-shaped cannulas. In the second experiment, three lysine-deficient diets were formulated to 0.36 g ileal digestible lysine/MJ digestible energy (DE), with lysine contributed from the three protein concentrates as the only source of lysine in sugar-based diets. An additional three diets were formulated with supplements of lysine to verify that lysine was limiting in the first three diets. The growth performance and retention of lysine by pigs given the six diets over the 20–45 kg growth phase were then determined. The apparent ileal digestibility of lysine in the three protein concentrates (proportion of total) was: cottonseed meal 0.74, meat-and-bone meal 0.78, soya-bean meal 0.89. Growth rates (g/d) of the pigs given the three diets formulated to 0.36 g ileal digestible lysine/MJ DE were significantly different (P < 0.001): cottonseed meal 377, meat-and-bone meal 492, soya-bean meal 541. The response of pigs to the addition of lysine confirmed that lysine was limiting in these diets. Crude protein (nitrogen× 6.25) deposited by the pigs was significantly higher (P < 0.001) for those given soya-bean meal (77 g/d), relative to meat-and-bone meal (66 g/d) and cottonseed meal (38 g/d). The proportion of ileal digestible lysine retained by pigs given the three protein concentrates was: cottonseed meal 0.36, meat-and-bone meal 0.60, soya-bean meal 0.75. The results indicate that values for the ileal digestibility of lysine in protein concentrates are unsuitable in dietary formulations as the assay does not reflect the proportion of lysine that can be utilized by the pig. It appears that, with heat-processed meals, a considerable proportion of the lysine is absorbed in a form(s) that is (are) inefficiently utilized.