Is your horse nutritionally wise?

IMG_8747Certainly not in the caloric sense! Put your horse in a field with a good crop of ryegrass and it will eat and eat. The net result is that it will become obese and the likelihood is that the animal will become insulin resistant and increasingly at risk of developing laminitis. As with ourselves, over fatness predisposes to disease so, over eating is definitely unwise.

What about nutrient wisdom? Frequently owners will observe horses licking and/or eating soil and will jump to the conclusion that the horse's diet is deficient in something, usually a mineral. There is limited evidence to show that herbivores may have an "appetite" for salt and phosphorus. In the case of the latter, phosphorus deficient dairy cattle have been observed to eat bones. This might be considered as a depraved appetite. The consumption of non-conventional food items is classified as pica and mostly these items would be regarded as non-nutritive. For example, foals are frequently observed to eat faecal material. Horses do not have the ability to select nutrients as a means of preventing disease. They rely on us to provide a balanced diet so one can provide self-help blocks such as Paddock Likits to promote an adequate nutrient intake.

What about the horse's ability to discriminate between plants and within plants? Horses are selective grazers/browsers and have distinct preferences which may be based on "mouth feel", taste, hardness, texture etc. We all know that horses tend to prefer sweet tastes, mint etc but preference for something does not indicate wisdom. Chomping through a packet of Polos might be nice and even a little naughty but it cannot be classified as wise. Horses may preferentially eat seed heads, buds etc before devouring the whole plant. Certainly horses select between pasture plants and will avoid grazing white clovers that contain a cyanogenic glucoside. This chemical complex releases a small amount of cyanide when the plant cell is damaged by a herbivore; a natural protection against slugs but also horses! It is not that the horse recognises cyanide as a danger but rather, it is the bitter taste of the cyanide that deters it from eating more. Where these white clovers grow they are evident in the pasture once the grasses have been grazed off as little mounds. Other sources of toxins are readily eaten (ragwort) or browsed (yew). Grazing studies have been conducted to determine if horses would select against the former when there was a plentiful supply of grass. Unfortunately, the horses failed to demonstrate any nutritional wisdom and ate some ragwort. What an animal eats can be as a simple result of preference, previous experience and/or social learning.



Written by Dr Derek Cuddeford at 14:39, 31 August 2012
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