Effect of Cooking Grain on Starch Digestion in Horse Feed

Effect of Cooking Grain on Starch Digestion in Horse Feed


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

The digestion of starch from raw cereal grains is often limited in the equine small intestine, with the feeding of raw grains frequently leading to hindgut starch fermentation and acidosis. To overcome the negative consequences of hindgut acidosis, which include colic and laminitis, grain processing methods that utilise heat, moisture and pressure have been developed to modify the starch structure in cereal grains and improve starch digestion in the small intestine.

The modification of cereal grain starch by these processing methods has been shown to enhance small intestinal starch digestion in the horse in vivo (Meyer et al. 1993; Richards 2003). However, recent studies (Richards 2004) have shown that some horses may lack the necessary concentration and activity of glycanase enzymes in their small intestine to effectively digest processed cereal grains. With this being the case it is possible that when heat processed cereal grains are fed, starch may still be delivered undigested to the hindgut.

A study was designed to quantify the enzyme digestion and fermentation characteristics of unprocessed and processed cereal grains. Two in vitro assays (Bird et al. 1999; Richards 2003) were used to simulate the small intestinal and equine hindgut fermentation characteristics of cereal grains commonly fed to horses. The results for corn and rice are presented below.

The heat processed grains were an average of 446% more enzymatically digestible than unprocessed grains (Table 1). In addition processed grains fermented faster in caecal fluid, producing up to 221% more lactic acid than their respective unprocessed counterparts (Table 1). The results of this study suggest that for horses with low glycanase activity and a corresponding limited capacity to digest starch in the small intestine, the feeding of processed cereal grains is potentially more hazardous than the feeding of raw cereal grains. The study also suggests that it may be beneficial from both a health and feed utilisation perspective to feed processed cereal grains in conjunction with glycanase enzymes to ensure the starch is completely digested in the small intestine.

Table 1:    Total starch, in vitro enzyme starch digestibility and in vitro fermentation characteristics of unprocessed corn, extruded corn, unprocessed rice and extruded rice. Enzyme digestibility was determined by incubating ground grain with amylase and amyloglucosidase at 39?C for 15 minutes. Fermentation characteristics were determined by fermenting ground grains in equine caecal fluid for 4 hours. The pH, volatile fatty acid concentrations and total lactate concentrations of the caecal fluid were measured at the conclusion of four hours.



  Extruded corn


    Extruded rice

Starch (%DM)





Starch digestion (% in 15 mins)





Caecal fluid pH





Total lactate (mmol/L)





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. Rec Adv in An Nut 12, 53 - 61.

Meyer, H., Radicke, S., Kienzle, E., Wilke, S., and Kleffken, D. (1993). Investigations on preileal digestion of oats, corn and barley starch in relation to grain processing. In "13th Eq Nut & Phys Symp", pp. 92 - 97, Florida.

Richards (2003) Enhancing Starch Digestion in the Equine Small Intestine. PhD Dissertation, UNE.

Richards, N. Choct, M. Hinch, G.N. Rowe, J.B. (2004) Examination of the use of exogenous a-amylase and amyloglucosidase to enhance starch digestion in the small intestine of the horse. An Feed Sci & Tech 114, 295 - 305