Forages such as hay and silage can vary considerably in their nutritional value to the horse. Factors like the species and variety of the forage, stage of growth when cut and method of preservation, influence the nutritional value.
It has been suggested that yeast supplements can improve digestibility, and thus help the horse make the most of lower quality forages. However, there have been conflicting reports about their value.
Laura Morgan, working with Dr Josie Coverdale and others in the department of Animal and Dairy Science, at the University of Georgia, Athens, looked at the effect of adding a yeast culture supplement to diets of varying forage quality.
Healthy adult horses were used in the study. They were fed a commercial grain mix, with or without a yeast supplement, with either high or low quality Bermuda grass hay. Bermuda grass is a common pasture grass found in tropical and sub-tropical regions around the world. The "lower quality" hay was, in fact, typical of hay used for feeding horses. The yeast culture*, containing Saccaromyces cerevisiae, was added to the morning grain mix.
Horses were fed according to body weight. The grain and forage rations were fed at 0.43% and 1.35% of body weight respectively. After allowing time for the horses to adapt to each diet, the scientists analysed fecal samples to calculate the digestibility of the diet.
They found that the quality of the forage influenced how efficiently the horses digested it. Diets based on high quality forage were more digestible than those containing low quality forage. Horses tended to eat more (on dry matter basis as a percentage of body weight) when fed the lower quality forage.
Overall, adding the yeast culture to the diet did not affect grain or hay intake (on a percentage of body weight basis). Nor did it influence digestibility.
But, the scientists did notice an effect when they looked specifically at the low quality diet. The yeast culture tended to increase the dry matter (DM) digestibility. It also tended to increase dry matter intake, and increase the digestibility of NDF (neutral detergent fiber – a measure of the fiber content of the feedstuff), hemicellulose and crude protein.
They suggest that supplementation with yeast culture can be used to improve the digestibility of diets containing low quality forage.
Equine Science Update
Effect of yeast culture supplementation on digestibility of varying forage quality in mature horses.
LM Morgan, JA Coverdale, MA Froetschel, I Yoon.
J Equine Vet Sci. (2007) 27, 260 - 265