247 In Vitro Characterization of Equine Fore- and Midgut Digestion

Abstract

Abstract Considerable advancements can be made in the field of equine nutrition and diet formulation, by improved feed characterization and the development of nutritional models, including in vitro models, to describe nutrient degradation. Methodologically, literature values for in vitro small intestine incubation times are widely variable ranging from 2 to 18 h. While some incubation times are selected to represent approximate mean retention times, conversely, insufficient in vitro incubation times and sampling time points could prohibit or result in inaccuracies characterizing nutrient degradability characteristics, ultimately affecting both degradability and digestion values and their use. The objective of this trial was to assess whether macronutrient degradability plateaus when digested for 2 h in a simulated gastric environment plus 8, 12, or 16 h in a simulated small intestinal environment. To replicate in vivo digestion, a pepsin-pancreatin approach was selected. The first step of this method replicates the gastric environment. Ten g of each test ingredient are weighed into beakers containing 60 mL hydrochloric acid (HCl; 0.1 M) and 0.4 g pepsin (~2,500 U/g) solution. Beakers are then covered and incubated for 2 h at 39 ℃ under constant stirring. One mL aliquots of the digestion liquid are sampled at 0, 5, 10, 20, 30 60, 90 and 120 min after the start of the gastric simulation. Before replicating intestinal digestion, samples are neutralized with sodium hydroxide and the pH is increased to 7. The second step of this method replicates the small intestinal environment. Fifty mL of pancreatin-phosphate buffer (350 U/g protease, 6,000 FIP U/g lipase, 7,500 U/g amylase) is added to the beakers, which are then covered and incubated for either 8, 12, or 16 h at 39 ℃ under constant stirring. One mL aliquots of the digestion liquid are sampled at 0, 5, 10, 20, 30 60, 90, 120, 150, 180 min and thereafter hourly up until the end of digestion (480, 720, or 960 min). Aliquot samples are analyzed for starch via a glucose assay, protein via o-phthalaldehyde assay, and lipids via gas chromatography. A model will is fit to the time point data to determine degradation rates and degradable fractions of the digested samples. Results from these analyses go beyond estimating gross nutrient and digestible nutrient values and inform on the rate of degradation of nutrients of equine feedstuffs and the impact of in vitro methodology. The resulting degradability values will be used in a mechanistic model of equine digestion which will inform precision feeding. Ultimately this will improve how we feed horses to reduce nutrient excretion into the environment and reduce the risk of metabolic conditions such as laminitis.