Prevention of Acidosis and Laminitis Associated with Grain Feeding in Horses

Abstract

It is well known that if horses consume large quan tities of rapidly fermentable carbohydrate in the form of starch or sugars they may develop laminitis. The pathway linking fermentable carbohydrate intake and damage to the lamellae of the hoof is not well under stood. It is, however, almost certain that the primary effect of high levels of sugars and starches in the gut is a rapid fermentation and the development of acidic conditions particularly in the cecum and colon. Severe acidosis in the gut, characterized by the accumulation of lactic acid and reduced concentration of volatile fatty acids, does not occur uniformly in all animals given an equal amount of grain (Aitchison et al. 1987). This variation between animals in the development of acidosis within the gut in response to high levels of grain is similar to the variation between animals in development of laminitis (Garner et al. 1977) in re sponse to carbohydrate overload. This provides further indirect evidence that gut acidosis may be the primary event leading to laminitis. The accumulation of lactic acid during rapid fer mentation can be controlled by antimicrobial feed ad ditives active against the gram positive bacteria such as Streptococcus bovis and Lactobacillus sp., which are primarily responsible for production of lactic acid at low pH. The feed additive virginiamycin has been shown in vitro (Nagaraja et al. 1987) and in studies in sheep (Godfrey et al. 1992) to be effective in control ling the accumulation of lactic acid. We have devel oped a formulation of virginiamycin for horses that retains its activity in the hindgut and, through its particulate nature, is also retained in the cecum. The aim of the experiment reported here was to investigate the control of laminitis using this formulation in horses given free access to a high-grain diet. Materials and Methods. Twelve standardbred horses weighing an average of 496 ±13 kg (mean ±SE) were used in the experiment. These horses came from a background of training and harness racing and were of unknown age. Before the start of the experiment, all animals were given a detailed clinical and lameness examination and were treated against intestinal par asites. Only animals that were completely sound and in good health were used in the experiment. There were three dietary treatments and four horses per treatment. The three groups were balanced for body weight. The three pelleted diets contained 85% ground maize, 13% soybean meal and 2% minerals and vitamins providing 13.9 MJ/kg digestible energy and 120 g/kg crude protein (Glen Forrest Stockfeeders, Perth, Australia). Two of the diets contained a feed additive containing virginiamycin (as Founderguard™