Using the slope ratio assay to determine availability of lysine in canola and cottonseed meals

Abstract

The study was developed to perfect the slope ratio chick bioassay for the determination of available lysine in three canola meals (CM) and one cottonseed meal (CSM) from Australian processors. The lysine bioavailability estimates for the test proteins meals using either LWG or FCR as the criteria for availability were (LWG, FCR): CSM 0.555, 0.609, CM Boree 1.114, 0.919, CM Riverland 0.905, 0.878, CM Melbourne 0.828, 0.876. CM, Boree exhibited the highest lysine availability compared with the other CM sources. Since Boree CM is an extruded extracted meal, this may suggest processing conditions as the main factor affecting availability. The availability of lysine from CM was 49-100% higher than that of CSM. processing conditions for oil extraction and differences in the type of condensed tannins which are present in both meals are responsible for the difference in lysine availability. When compared the availability with the apparent ileal digestibility from a previous study. For CSM, both methods agreed well (slope ratio assay 0.555 c.f. ileal digestibility method 0.515), thus ileal digestibility of lysine appears to provide a reasonable estimate of lysine availability in CSM from Narrabri. The lysine availability of CM from Boree, Riverland and Melbourne were 1.114, 0.905, and 0.828, respectively which were 51, 25, and 20% higher than the lysine ileal digestibilities obtained on similar CM samples using the ileal digestibility method. These results suggest that the two methods compare poorly for CM. The explanation for this outcome is difficult and further investigation is needed.