Effect of heat on the apparent ileal digestibility and availability of lysine in field peas for growing pigs.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 EFFECT OF HEAT ON THE APPARENT ILEAL DIGESTIBILITY AND AVAILABILITY OF LYSINE IN FIELD PEAS FOR GROWING PIGS R. J. VAN BARNEVELDA, E. S. BATTERHAMA, and B. W. NORTON B *NS W Agriculture, Wollongbar Agricultural Institute, Wollongbar, N.S.W. 2477. BDept of Agriculture, The University of Queensland, St Lucia, Qld 4072. In meals of low lysine availability, such as cottonseed meal, reduced ileal digestibility only accounts for part of reduced availability (Batterham et al. 1990). It is possible that heat applied during processing affects lysine in such a way that some of it is apparently digested in a form that is unavailable to the pig. The aims of this study were to confirm the above hypothesis, and to determine the relationship between apparent ileal digestibility and availability of lysine in field peas subjected to a range of heat treatments. Field peas (var. Dundale) were heat-treated at either 110, 135, 150, or 165OC using forced-air dehydrators. The apparent ileal digestibility was determined in pigs fitted with simple T-piece cannulae in the terminal ileum. Diets were sugar-based and contained 40% of the respective field peas. Lysine availability in the field peas was assessed with a slope-ratio assay (Finney 1964). Diets were wheat-based and were formulated to contain graded levels of standard (free) and test (field pea) lysine. They were equalised for fibre and digestible energy, and all other essential amino acids were added to ensure a 15% excess relative to lysine. The pigs were fed frequently (3 h) on a 3 times maintenance (0.5 MJ DE wkgoe7') feeding regime (adjusted weekly) over the 20 to 45 kg growth phase, and were then slaughtered. Linear regression coefficients of response of feed conversion efficiency (FCE) on an empty-body basis to increasing dose level of test protein and standard lysine were calculated and the ratio of the linear regression coefficients, test protein:standard lysine, provided an estimate of availability of the lysine in the test protein. Table 1. Apparent ileal digestibility and availability of lysine (proportion of total) in raw and heat-treated field peas Preliminary results show a linear decrease in ileal digestibility (PcO.05) and availability (PcO.05) with increasing heat treatment (Table 1). They also reveal a much greater reduction in availability than ileal digestibility when heat is applied. The higher availability in the raw peas compared to the ileal digestibility may be due to either the fact that apparent digestibility was determined using diets containing only low levels of crude protein, and hence true digestibility may be substantially underestimated, or imprecision in the slope-ratio assay. These results indicate that with increasing heat application to protein concentrates, lysine availability is affected to a greater extent than ileal digestibility. Therefore, ileal digestibility is not a reliable indicator of availability with heat-treated meals. BATTERHAM, E. S., ANDERSEN, L. M., BAIGENT, D. R., DARNELL, R. E.: and TAVERNER, M. R. (1990). Br. .I. Nutr. 64: 663-7. FINNEY, D. J. (1964). ` Statistical Method in Biological Assay.' 2nd Edn. (London: Griffin.) 290