Effects of isoenergetic quantities of a low‐starch muesli feed high in fat and fibre vs. oat grains on the glycemic and insulinemic responses and feed intake patterns in sport ponies

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Compound feeds rich in ‘dietetic fibre’ are gaining popularity, particularly for performance horses, including sport ponies. These feeds can provide a more balanced diet (Richards et al., 2006) because grains are no longer fed in isolation. It is also supposed that they prevent gastric and intestinal problems in particular in sport horses predisposed to gastric ulcers due to high stress levels (Bergero et al., 1998). Nicol et al. (2005) described an impact of a diet high in fat and fibre (FF) vs. starch and sugar on the behaviour of young horses after weaning. Overall, the horses received a FF diet appeared less stressed. Nevertheless, cereal grains serve as an important energy source in which starch breakdown and absorption as glucose in the small intestine is desired. Because pancreatic amylase activity is particularly low in horses in a species comparison, precaecal starch digestion is restricted with clear differences between grain types and a reliably high digestibility with oat grains only (see for example Wolter and Gouy, 1976; Arnold, 1982; Heintzsch, 1995; Meyer et al., 1995). Previous studies described an impact of thermal processing of diverse types of cereal grains on precaecal digestibility of starch (Meyer et al., 1995; Julliand et al., 2006; Zeyner, 2008) and glycemic as well as insulinemic responses in horses (Vervuert et al., 2003, 2004, 2007, 2008). Särkijärvi and Saastoamoinen (2006) found a tendency of decreased digestibilities due to heat treatment. Bochnia et al. (2015a,b) confirmed the huge diversity of starch morphology in oats, barley and maize and further described sophisticatedly diverse morphological characteristics of distinct oat varieties, which might also influence metabolic responses. The glycemic index (GI) influenced by diverse treatments of cereal grains can provide information on the blood glucose concentrations induced by different foods after ingestion (Rodieck and Stull, 2007).
In addition to the obvious benefits of glucose provision from starch digestion in the small intestine, frequent ingestion of high‐glycemic diets and the subsequent downregulation of insulin receptors in target tissues might lead to a state of insulin resistance (Treiber et al., 2005), which should be assessed as critical if the condition becomes chronic. Concentrates that do not induce high postprandial (PP) glycemic and insulinemic responses and have a low GI are thus required, particularly for animals with impaired insulin sensitivity such as equine metabolic syndrome or polysaccharide storage myopathy (Williams et al., 2001; Zeyner et al., 2006). This strategy, however, may also be advantageous for healthy growing and adult horses, helping them to avoid the possible detrimental consequences associated with metabolic stress. Special diets for horses which include different ingredients with low GI as an energy source, such as chopped hay (alfalfa, timothy, GI < 55; Rodieck and Stull, 2007), dried carrots, or oil can influence feed intake behaviour because the majority of them requires a more intense chewing process (Bonin et al., 2007; Bochnia et al., 2008; Bochnia, 2009). The variable likely to affect chewing frequency (CF) and intensity (CI) are the nature of the food, especially its fibre content and particle size (Leue, 1941; Baker, 2002; Bonin et al., 2007).The body size and particularly the species and breed of the animal are also important influencing variables (horses: Meyer et al., 1975; cattle: Bae et al., 1983; mammals in general: Druzinsky, 1993; Shipley et al., 1994; Gerstner and Gerstein, 2008). A comparison of the literature examining chewing frequencies in horses and ponies (Meyer et al., 1975; Shingu et al., 2001; Brüssow, 2006; Bochnia, 2009) seems to be in line with the general trends reported by Shipley et al. (1994) for mammalian species, who reported an interspecific trend of decreased CF with increasing bwt.
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