Protein has been identified as a major reason that people purchase a horse feed, with anecdotal explanations offered for the poor prediction of response of horses to their rations, particularly in the sport horse market. The current research identifies through hierarchical cluster analysis that the myriad of riding feeds offered on the South African market fall into only four simple categories on the basis of wet chemistry. Feeds were subjected to the in vitro gas production technique (IVGPT) described by Pell and Schofield (1993), using equine faecal inoculum. Gas profiles, corrected for control fermentation profiles in the absence of substrate, were fitted to the model described by Campos et al. (2004) to derive GP kinetics. Gas production kinetics, and information in respect of pH, degradation efficiency, lag time and apparent and true digestibilities were obtained. The feeds were tested for glycaemic response in miniature horses using the hexokinase method with deproteinization using an auto analyser (Roche Diagnostics). Blood glucose parameters of feeds (mean, peak, slope and time to peak and area under the curve) in each group were compared by analysis of variance and regression with covariates. In vivo analysis of rates of passage and digestibility using using post-prandial percentages of acid insoluble marker collection was used to study the gastrointestinal process, to indicate foregut and hindgut compartmental flow. The need to balance nitrogen levels with a proportional supply of fermentable carbohydrate contradicts widely used protein intakes in the horse. In vitro fermentation was used in an analysis of nutrient synchrony, to identify optimal fermentative capacity for utilization of horse feeds. The characteristics of horse feeds were related to requirement and were composited in an analysis of the representation of horse feeds that would best reflect optimal utilization in the horse, to produce a method of feed characterisation that would lead to the optimal prediction of response of horses to feeds offered to South African horses. / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.