Walter Gerrits

After completing his PhD on growth modeling in pre-ruminant calves in 1996, Dr Gerrits worked as a research scientist for TNO Nutrition & Food Research Institute. He is a specialist in quantitative animal nutrition and has worked for Wageningen University for more than twenty years, holding a personal chair since 2016 and leading the Animal Nutrition Group since 2021. His research focuses on digestive physiology and macronutrient metabolism in various species, mostly pigs and calves. Dr Gerrits has focused on interactions between nutrition, health and welfare. In whole-body metabolism studies, Dr Gerrits combines indirect calorimetry with stable isotope tracer technology. Understanding digestion kinetics is a key item in his research across species. In pigs, his research has focused on the quantitative impact of suboptimal health on nutrient digestion and metabolism. Twenty-five PhD students have completed their PhD under his supervision with 9 more underway. His publication record comprises more than 170 papers in peer-reviewed journals.

Traditionally, feed ingredients are evaluated based on their measured extent of digestion. Awareness increases that in addition to the extent, the kinetics of digestion affects the metabolic fate of nutrients after absorption, and relative functionalities modifying physiology of the animal. In current feed evaluation system, mostly the extent of nutrient digestibility is considered as the main determinant of the quantity of nutrients that can be absorbed from the diet. But differences in kinetics can be profound. In his presentation, Walter Gerrits explained that kinetics gives a better understanding of the digestion process, the synchronization of nutrients and of the adequate feeding of the colon microbiome, which may have several health implications. He illustrates that dietary regulation of nutrient absorption kinetics primarily takes place in the stomach, being affected by dietary physicochemical properties like water binding capacity and particle size. Then, he demonstrates the importance of dietary fibres in the regulation of digesta transport through the gastro-intestinal tract, focusing on digesta phase separation and retention times in the stomach. Then, Walter Gerrits discusses the impact of dietary proteins flowing into the hindgut and the end-products of protein fermentation that are formed. A whole range of product and metabolites can be produced during protein fermentation and absorbed but little is known on their toxic effect on the body. He concluded that future feed ingredient evaluation should consider hydrolysis rates as true properties of nutrients, physico-chemical properties of ingredients and should account for interactions between ingredients.