An investigation on the impact of feed grain anti-nutrients on monogastric animal digestion with a focus on exogenous feed enzymes

Supplementation of monogastric animal feed with exogenous enzymes has become standard practice with many positive impacts observed in animals and the environment. Recently there has arisen a need to investigate the effects that anti-nutrients, specifically those found in sorghum grain, might have on the activity of the exogenous feed enzymes. Consequently, we sought to better understand the role played by one anti-nutrient, polyphenols, and its role in muted exogenous phytase and protease performance in monogastric diets containing sorghum. Polyphenols from three commercially relevant sorghum grains, and two commercial tannin extracts, were first characterised to better understand the anti-nutrients of interest. Metabolomic analyses revealed a complex polyphenol-like environment which lacked the traditional, large polyphenol anti-nutrients of historic sorghum grains. A multi-method approach allowed for layers of complexity to be revealed and indicated that simpler spectral methods were better suited for fingerprinting than mass spectrometry. The polyphenol extracts were next tested as in vitro inhibitors of exogenous protease and phytase activity. The two commercial tannins, grape seed and quebracho wood, strongly inhibited both enzymes at low concentrations. Sorghum polyphenol extracts had a weaker effect on both enzymes, particularly the protease. Finally, the extracts were incorporated into a standard poultry diet in a simulated in vitro digestion model to measure their effects on nutrient digestibility. In this complex environment, all extracts had minimal effects on both protein and phosphorus digestibility. A rapid mass spectrometry method was trialled to fingerprint the supernatant of different diets with varying degrees of success. The results found in this work indicate that while modern sorghum grains may have minimal impact on exogenous enzyme activity, attention is needed at the metabolite level to determine which anti-nutrients may be implicated in sorghum’s performance variability.