Maintenance of normal gut function is achieved through a combination of good management practices and individual animal nutrition. Supplemental products also form part of that combination. The horse has evolved to require a minimum amount of dietary fibre as a food source for the micro-organisms located in the caecum and large intestine, collectively called the hindgut. In addition, horses can digest very little starch at any one time and consequently, the small intestine struggles to deal with concentrate meals (coarse mixes, straights etc) containing more than 3-4g starch per kilogram of body weight per meal – commonly known as starch overload. For example, a 500kg horse should be offered no more than 1.5-2kg of starch per meal. Any starch that escapes digestion in the small intestine will end up being fermented by microbes in the hindgut (particularly the caecum) resulting in the increased production of lactic acid.
Disruption of normal hindgut function by less than adequate dietary fibre or excess dietary starch often reduces the ability of the hindgut to maintain a near-neutral pH, which can lead to acidic conditions, often referred to as acidosis. Gut disturbances such as acidosis, are one of the many factors implicated in colic. Additionally, many microbes in the caecum cannot survive this low pH (particularly the fibre-digesting bacteria) and die, releasing bacterial endotoxins into the blood stream increasing the risk of laminitis. Acidosis actually relates to a lowering of blood alkali reserves (this means a lack of buffer to compensate for the increased acidity) and many horses suffer from a sub-clinical form, particularly those in hard work, coupled with limited access to forage. In this situation it may be prudent to consider a supplement or additive to help beneficially modify the hindgut environment.
Live strains of the yeast, Saccharomyces cerevisiae, are used in animal nutrition to enhance fibre digestion in both ruminants and non-ruminants. These strains have the ability to metabolise nutrients in an anaerobic environment and promote the growth of beneficial bacteria, including those that can utilise lactic acid. One particular strain, 1026, is effective at stimulating fibre-digesting and lactic acid-utilising bacteria. This in turn, creates a more stable gut environment, reducing the risk of gut disturbances, such as acidosis leading to laminitis and potentially, insulin resistance. Studies have demonstrated improved fibre digestibility and increased caecal pH in horses on high starch diets receiving a live yeast culture, Yea-Sacc® from Alltech, compared with unsupplemented horses. This higher pH stabilises the caecal environment, which is conducive to improved feed efficiency and prevention of gut disturbances. Increased fibre digestion was also noted by Jouany et al. 2008, irrespective of whether the diet was high in fibre or starch.
The impact of live yeast appears to go beyond simply increasing fibre digestion in some cases. Increased utilisation of phosphorous in horses supplemented with S. cerevisiae cultures, such as Yea-Sacc, has been described, which may be of interest when feeding the aged horse.
Beneficial effects have also been seen in mares during gestation with regard to milk quantity and quality, resulting in faster growing foals. As the foetus grows in size during the 3rd trimester of gestation, the room available for food in the mare is significantly reduced, which can result in loss of body condition. Improving nutrient digestibility at this stage is important to minimise loss of condition of the mare. Due to the mode of action of supplements, such as Yea-Sacc, energy, fibre, calcium and phosphorous digestibility are all increased. Higher milk yields (+5-15%) and nutrient content (more energy and protein) have also been demonstrated in horses, as well as other species. Foals receiving milk from these supplemented mares tend also, to grow more quickly than those from unsupplemented dams.
One digestive problem that frequently occurs in young animals is diarrhea, resulting in poor hydration status and ill thrift. As the feeding of antibiotics as a prophylactic measure is restricted in some countries, research has been conducted into more natural solutions. The feeding of
mannanoligosaccharides (MOS) to reduce the threat of harmful bacteria has attracted much attention in both the horse and livestock industries. MOS are derived from the outer cell wall of yeast and are known to have the capacity to bind these harmful bacteria, preventing them sticking to, and colonising, the gut wall. As a result, the strain on the animal’s immune system is reduced and more energy can be directed towards growth. It has been demonstrated that supplementing the mare with MOS (Bio-Mos® from Alltech) resulted in higher immunoglobulin (antibody) concentrations in the colostrum, providing the nursing foals with greater defence against disease and, consequently, increasing their growth rate.
Maintaining gut health minimises the risk of gut disturbances, respiratory and performance problems. Natural solutions include digestive enhancers in the form of live yeasts. However, there is no doubt that a holistic approach to feeding is conducive to maximising gut function and one must never forget the basic rules of feeding.