PICKY EATERS.qxd:Jerkins feature.qxd
4/10/08
What drives appetite? The mechanisms involved in controlling feed intake and appetite are very complex, but have been studied extensively in humans and other species. Similar work in this area in horses is limited but progressing. The hypothalamus appears to be the critical area of the brain that is involved in the regulation of food intake, and it represents the body’s thermostat, helping to regulate body temperature. This area of the brain produces a number of protein-like chemicals (peptides) that help to control feed intake, through either stimulatory or suppressive effects on appetite. The hypothalamus also responds to a number of chemicals, hormones and nutrients circulating in the blood, and some of which have previously been investigated in horses. Leptin produced by adipose tissue, insulin produced by the pancreas, ghrelin and obestatin produced in the gut and triiodothyronine (a thyroid hormone) produced by the thyroid gland are all involved in regulation of feed intake and appetite (Dhillo 2007). In addition, the products of carbohydrate, fat and protein digestion are also known to be involved in the regulation of appetite.
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Some early work that was carried out by Ralston and co-workers in the 70s and 80s explored the effects that blood glucose and insulin have on feeding behavior in horses. Perhaps not surprisingly, they reported that the elevation in glucose and insulin concentrations in blood, which are seen following consumption of a cereal based concentrate feed, appear to delay further feeding (Ralston 1986). Some research has also been carried out on the role of leptin, which is a hormone produced by the adipose tissue, in horses. The function of leptin is to suppress appetite, and circulating levels of leptin are increased with increasing body fat content. Therefore, one would expect that in fit lean racehorses, circulating leptin concentration would be reduced, in order to drive appetite and achieve feed intake sufficient to meet the increasing energy demands of training. This certainly appears to be the case, with the circulating level of leptin being lower in young fit Standardbred racehorses compared to mature unfit Standardbred horses (Gordon et al. 2007). In this same study, these authors also reported that ghrelin and obestatin, which are both reported to stimulate appetite, were also significantly greater in the fit versus the unfit
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