by Dr Derek Cuddeford, Royal (Dick) School of Veterinary Studies, University of Edinburgh
Both horses and ruminants are members of the ungulate group of animals which can be subdivided into the order Perissodactyla or odd-toed ungulates and the order Artiodactyla, the even-toed ungulates. The bodyweight of members of the latter is borne about equally by the third and fourth toes and includes pigs, hippos, camels, deer, giraffes and of course sheep, goats and cattle. The sub-order amongst the Artiodactyla is the Ruminantia characterized by animals that chew their food, swallow it and then later regurgitate it for further chewing as in “chewing the cud” (this is no reference to yours truly!). The bodyweight of the Perissodactyla is almost all borne by the third toe and these animals have relatively simple stomachs relying on fermentation in the large intestine to degrade plant material rather than the complex four-chambered stomach possessed by ruminants. We are familiar with members of this group which includes rhinos and of course horses, donkeys, and zebras; the latter three belonging to the family Equidae.
When answering the question posed one must consider firstly the basics of the digestive process in both species. Ruminants spend half the time chewing when they eat compared to horses (8h vs 16h) but, whilst ruminating and chewing the “cud” they spend the same amount of time (8h) as when eating. Thus, in total horses and ruminates chew their food for about the same overall length of time. The swallowed bolus is exposed to random fermentation in a ruminant’s stomach (via enzymes produced by the microorganisms present) over quite a long period of time (akin to being in a waiting room) before being made available to the enzymes of the host animal in the small intestine. This means that food is effectively predigested and substrates such as starch may be fully degraded prior to entering the small intestine. In marked contrast horses thoroughly process their food (grinding) before swallowing it. Residence time in the stomach is short and thus it merely acts as a sort of transit lounge although there is a very small amount of fermentation. Food entering the small intestine of the horse is only predigested to a very small extent so that a substrate such as starch is very similar to the form in which it was ingested. It is clear from the foregoing that the digestive strategies of the horse and ruminant animal are very different. However, what is so interesting is that they are both herbivores and thus adapted to survive on forage. It should be remembered that certain members of the Ruminantia have a specialized mouth shape that enable them to browse. A good example is the narrow incisor arcade of the giraffe that allows it to gather leaves of the thorny Acacia tree without damaging its face; it can be very selective helped by the fact that its tongue is 18 inches (45cm) long. The wide flattened incisor arcade of the horse is designed for grazing but, given the chance, they will browse your neighbour’s beech hedge to extinction. Whilst they may not be as selective as a giraffe they are very selective compared to a cow. The top lip of a cow is fairly immobile whereas as that of a horse is incredibly flexible allowing the horse to pick and choose what it eats. When cows graze they just put their heads down and hoover up everything that is available including odd nails and even bits of barbed wire. Of our domestic ruminants it is only really the goat which will browse, eating anything from knickers on the washing line to any hedge or plant that it can get its teeth into; nothing is sacred when it comes to goats!
Forages that are fed to ruminants include grass and all grass products in the form of silages (big bale, clamp and tower silages), hays (field-cured, barn dried) as well as legumes such as clovers, sainfoin and alfalfa. The other major forage type is whole-crop maize silage. In addition to these traditional forages ruminants are also fed potatoes, swedes, turnips and other root crops as well as industrial byproducts such as sugar beet pulp, distillery and brewery grains. All of the foregoing are safe to feed to horses provided of course that care is taken over the feeding routine (meal frequency and size) and that appropriate adaptation is allowed as well as regulating the quantity fed. For example ad libitum hay/silage would be alright but ad libitum potatoes would not be a good idea. Some of the above feeds can play a part in the daily ration of a horse whereas other materials can constitute the whole ration.
All the cereal types routinely fed to ruminants can be fed to horses although they should be cooked (micronized, steam-flaked, extruded) with the exception of oats which are best fed raw. Again, these materials can only form part of the horse’s daily ration.
Compound feeds produced for ruminants contain, in most cases, the same raw materials as used to produce horse compound feeds and thus in theory ruminant compounds could be fed to horses. However, any medicated feed (those produced under a veterinary written direction) produced for a specific medicinal purpose should not be fed to any horse or pony. Of course, ruminant animals are produced for their milk or meat so substances such as dioxin which can get into the food chain can be a serious worry; never more so than after the serious flooding in Germany during summer 2013 when grazing areas were polluted. Feed produced in farm animal feed mills is often contaminated with substances that are prohibited in the competitive horse industry and since cows do not feature in the Derby very often this is not a problem in the Agricultural Industry. Simple examples would be caffeine and theobromine residues whose presence in a horse feed and thus in the horse would lead to disqualification in a competition if the horse was blood-tested. Another major worry in a farm animal feed mill would be the risk of cross-contamination resulting from the production of pig, poultry and ruminant products through the same equipment. For example coccidiostats are commonly used in poultry diets and can be fatal for horses whilst farm animals are not considered to be at risk from such substances. Thus, if your horse is not involved in competitions and in the light of the provisos mentioned above it would be alright to feed ruminant products but you would have to be very clear about the provenance of the product used.
Check the label
One could of course turn the question on its head and ask “Is it safe to feed horse compounds to ruminants”? The answer is perhaps rather surprising. Feeding competitive horse and stud/breeding diets to sheep and goats would almost certainly kill them! This is because some horse owners seem to want to ignore current scientific knowledge and insist that ridiculously high levels of copper are included in such diets. There is a belief that high levels of copper will prevent/cure bone lesions in growing horses and that performance horses will benefit as well. Thus, most feed manufacturers include levels of copper that will supply well in excess of established need. No-one dares take a stand on this for fear of losing market share in a very competitive industry and so all feed manufacturers oversupply copper in certain of their products.
Finally, most ruminant feeds can be fed to horses whilst some horse feeds cannot be fed to certain ruminants. Take a look at some bag labels on horse feed and see what it says…