I . A slope-ratio assay was developed with growing pigs to determine the availability of lysine in five protein concentrates. The basal diet contained 5.2 g lysine/kg and six levels of lysine, in 500 mg/kg increments, were used to determine the pig's response to standard lysine. The protein concentrates were incorporated into the basal diet to provide five levels of total lysine, again in 500 mg/kg increments, at the expense of wheat starch. A daily feeding scale based on live weight was used to ensure similar nutrient intakes. Pigs were fed at three-hourly intervals to ensure the utilization of free amino acids in the diets. Four pigs were allotted to each dose level and response was assessed over the 20-45 kg growth phase.2. Potency estimates for available lysine in the five protein concentrates varied, depending on whether live-weight gain or carcass gain was used as the criterion of response. Carcass gain was considered more appropriate as it was not influenced by variation in gut fill. Availability of lysine in the five proteins, using carcass gain/d were (proportion of total) cottonseed meal 0'39, fish meal 0.89, meat-and-bone meal 0.50, skim-milk powder 0.88 and soya-bean meal 0.87.3. Rat slope-ratio assay results for available lysine in the five protein concentrates were in general agreement with those from the pigs. In contrast, thedifferences in available lysinewere not detected by thechemical Previous work (Batterham et al. 1978) showed that for growing pigs, the content of available lysine in locally produced cottonseed meal, two meat meals and sunflower meal was approximately 60% less than that in rapeseed meal, skim-milk powder and soya-bean meal. Similar differences were detected with a slope-ratio assay with rats but not with the chemical Silcock available-lysine assay as developed by Roach et al. (1967). In view of these differences, it seemed appropriate to attempt to quantify the available lysine content of the major protein concentrates for pigs and to evaluate the efficiency of some of the different techniques for estimating available lysine. This paper reports the results of a slope-ratio assay that was developed with growing pigs to determine the availability of lysine in five protein concentrates. Lysine availability in these proteins was also estimated by a slope-ratio assay with rats, the Silcock available-lysine technique and by ihe direct fluorodinitrobenzene (FDNB)-available-lysine assay (Carpenter, 1960).Pig slope-ratio assay Diets. For the pig assay, five protein concentrates were assayed in the one experiment. This involved the use of thirty-two diets; the basal diet (blanks), six diets to determine the pig's response to standard lysine and twenty-five for the five protein concentrates (five/ protein concentrate). The basal diet contained (g/kg) : wheat 730, wheat gluten 50, L-lysine monohydrochloride (anhydrous) I .03, DL-methionine 0.30, L-threonine 0.70, mineral and vitamin premix 5, bone flour 30, and starch 182.97 (Table I). The wheat was a high-protein

I. The availability of lysine in nine vegetable-protein concentrates was assessed using the slope-ratio assay for growing pigs and rats. Diets were equalized for crude fibre using solka floc to minimize any possible effects of variation in fibre content on availability estimates.2. The availability of lysine in the nine proteins for pigs, using food conversion efficiency (FCE) on a carcass basis as the criterion of response were (proportion of total): cottonseed meal 0.39, lupin (Lupinus angustijolius) seed meal no. 1 0.37, no.

2. The efficiency of utilization of free lysine with once daily feeding relative to frequent feeding was 0.53 using carcass gain as the criterion of r:sponse (P < 0401), and 0.56 using food conversion efficiency on a carcass basis (P c 0401). These estimates were lower than estimates of 0.67 using live-weight gain (P c 0.01) and 0.77 using food conversion ratio on a liveweight basis (P < 0.05). 3. The results indicate that current estimates of the lysine requirements of pigs that are based on responses to supplements of free lysine undsr once daily feeding regimens may be 10-30% over-estimated, as a result of incomplete utilization of the free lysine.

1. The availability of lysine in seven vegetable protein concentrates was determined using the slope-ratio assay with growing pigs and rats and with two chemical techniques.2. With pigs, estimates of availability were lower using carcass compared to live-weight values, but there was no consistent effect of including food intake in the criterion of response. Availability estimates, using food conversion efficiency on a carcass basis were (proportion of total) linseed meal -0.23, lupin-seed meal 0.74, rapeseed meal no. 1 0.97, no. 2 0.77, sunfiower meal no. 1 0.59, no. 2 0.66, no. 3 0-54.3. Availability estimates for lysine with rats were also lower using carcass compared to live-weight values. Estimates based on food conversion efficiency were higher than those based on weight gain. Availability estimates in lupin-seed meal and sunflower meals were in general agreement with the pig estimates, whilst that with linseed meal was considerably higher (0.82). Assays were not conducted with rapeseed meal due to problems of food rejection with this meal. Batterham et al. (1979) reported the development of a slope-ratio assay for available lysine in protein concentrates with growing pigs. Availability estimates using this assay indicated substantial differences in the availability of lysine in cottonseed meal (0.43) and meatand-bone meal (0.49) compared to fish meal (0.89), skim-milk powder (0.85) and soya-bean meal (0-84). These. differences were also detected by slope-ratio assays with rats but not by the chemical Silcock available-lysine assay (Roach et al. 1967) nor by the direct fluorodinitrobenzene (FDNB) available-lysine test (Carpenter, 1960). This paper reports the determination of available lysine in a series of vegetable protein concentrates using the slope-ratio assay with pigs and rats. The protein concentrates were also analysed with the Silcock (Roach et al. 1967) and direct FDNB (Carpenter, 1960) available-lysine assays to determine if these techniques were applicable in these meals. Previous work (Batterham et al. 1979) had also indicated that slope-ratio values based on carcass values were more applicable with pigs than those based on live-weight values; this aspect was also examined for slope-ratio assays with rats.

I. Eight protein concentrates were compared on a total lysine basis in lysine-deficient diets for pigs during the 20-45 kg growth phase. Each diet was also supplemented with free lysine to verify that lysine was the first limiting amino acid.2. With fish meal, skim-milk powder, rapeseed meal and soya-bean meal growth rates and feed conversion efficiencies were similar and superior (P < 0.05) to those produced with cottonseed meal, two meat meals and sunflower meal.3. The response to added free lysine confirmed that lysine was the first limiting amino acid in all diets except skim milk, where the growth response was not significant (P < 0.05). 4.The growth response of the pigs indicated that the availability of lysine in cottonseed meal, the two meat meals and sunflower meal was reduced by approximately 60% compared to that in the other protein concentrates.5. Rat bio-assay estimates of the availability of lysine in the protein concentrates were in general agreement with those calculated from the response of pigs. There was little relationship between the Silcock estimates for lysine availability for the cottonseed, meat meals or sunflower meal relative to either the rat bio-assay estimates or the response of pigs.Lysine is normally the first limiting amino acid in cereal-based diets for growing pigs (Braude, Mitchell, Myres, Newport & Cuthbertson, I 972). This limitation is usually overcome by the inclusion of protein concentrates. The availability of lysine in these concentrates may be reduced if severe heat is used during processing. Consequently, techniques for estimating lysine availability have been developed. The most widely adopted of these are based on reactions with the free €-amino group of lysine (e.g. Carpenter, 1960; Roach, Sanderson & Williams, 1967).Recent indications are that lysine availability is largely unaffected when modern processing procedures are properly applied. For example, Milner & Westgarth (1973) reported values of 0.93-0.97 for availability of lysine in a selection of protein concentrates. Taverner & Rayner (1975) also reported values from 0.81 to 0.91 for available lysine in vegetable proteins processed by either expeller or solvent extraction; in subsequent pig experiments, both total and available lysine values were closely correlated with pig performance. Thus, if lysine availability is relatively unaffected during processing, then total lysine values are the most convenient method for formulating diets. In the work reported here, total lysine was evaluated as a predictor of the lysine status of a range of protein concentrates. EXPERIMENTAL Pig dietsDiets were formulated to contain 6. I g lysine/kg, with the protein concentrates contributing 3 g/kg and wheat 3.1 g/kg ( Table I). These diets contained approximately 75 % of the estimated requirements of pips for lysine (Agricultural Research Council, 1967). The cottonseed, rapeseed and sunflower meals were 'prepress' solvent-extracted ; the soya-bean meal was solvent-extracted ; the skim-milk powder was spray-dried and the fish m...