Media Room: Info Sheets

Aug 14th, 2008

Grain Feeding Practices and their effect on Hindgut Health in Racing Thoroughbreds

NERIDA RICHARDS

Equilize Horse Nutrition Pty Ltd, PO Box 373, Nicholson  VIC  3882 nerida@equilize.com.au

Thoroughbred horses in training are commonly fed large quantities of cereal grains on a daily basis. A survey was conducted to provide detailed and current information on grain feeding practices within the thoroughbred racing industry and to determine the likely impact of these practices on the horses' hindgut environment.

Seventy two thoroughbred trainers in country and metropolitan regions of NSW were surveyed on a face to face basis. During the survey visit, grain and chaff portions of the diet were weighed and samples of grain and faeces were collected. Grains were analysed for in vitro starch digestibility (Bird et al. 1999) Faeces were analysed for pH, dry matter, starch content, nitrogen content, volatile fatty acid and lactic acid concentrations.  

Results of the survey showed that oats, corn and commercial premixed diets were the grains most commonly fed to thoroughbred horses, with 80.6%, 73.6% and 73.6% of trainers feeding these grains respectively. Barley was fed by one third of thoroughbred trainers. The use of processed grains was uncommon with only 20% of grains being fed in a processed form. On average, horses were fed 7.3 kg of grain/day. Oats (3.6 kg/day), premixed feeds (2.5 kg/day) and corn (1.7 kg/day) were fed in the greatest quantities.

Mean faecal pH was 6.5 but values as low as 5.5 were observed. Twenty seven percent of faecal samples had a pH lower than 6.2, which is considered below the optimum pH for cellulolytic and lactate utilising bacteria (Leek, 1993). Eighty percent of faecal samples had an acetate: propionate ratio lower than 4.7: 1, which is the level expected during fibre fermentation (Leek, 1993). There was a strong negative relationship between faecal propionate concentration and faecal pH (R²=0.76, n=49). This relationship suggests that the decline in pH is due to the fermentation of starch by amylolytic bacteria, who characteristically produce more propionate during fermentation than cellulolytic bacteria (Leek, 1993). Faecal lactate concentrations were variable, ranging from 0.05 mmol/L to over 3 mmol/L.

In an attempt to establish a relationship between the amount or type of grain fed and measured faecal parameters, it was observed that neither the amount of oats (average in vitro starch digestibility 61%) or commercial feeds (average in vitro starch digestibility 59%), nor the total quantity of grain fed to individual horses/day held any significant relationship to the concentration of organic acids in the faeces. Likewise, the amount of chaff fed had no significant effect on faecal parameters. In contrast, the total quantity of corn (average in vitro starch digestibility 36%) fed to individual horses/day was positively related to total faecal acid concentration (R²=0.28, n=49). Over 90% percent of corn was fed to horses cracked or whole.

The results from this survey demonstrate that grain feeding practices are resulting in some degree of hindgut starch fermentation and acidosis in over one quarter of horses studied. These digestive upsets will possibly reduce a horse's ability to perform athletically and could also end a horse's career if complications such as laminitis develop. The survey results also indicate that many of the problems are caused by feeding grains with a low small intestinal digestibility. The careful selection of grains with superior small intestinal starch digestibility characteristics or the use of alternative low starch, high energy feeds should become a priority for trainers who wish to avoid these problems.

Bird, S. H., Rowe, J. B., Choct, M., Stachiw, S., Tyler, P., and Thompson, R. D. (1999). In vitro fermentation of grain and enzymatic digestion of cereal starch. Recent Advances in Animal Nutrition 12, 53 - 61.

Leek, B. F. (1993). Digestion in the Ruminant Stomach. In "Dukes Physiology of Domestic Animals" (M. J. Swenson and W. O. Reece, eds.), pp. 387 - 416. Comstock Publishing Associates, London.