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Feeding Herbivores



     The feeds we give to herbivores are not the same as those for carnivores.  People, pigs, fish, cats and dogs are carnivores, which require their food to be easily digested.  We require our protein to be balanced in the amino acid content, our vitamins to be pre-manufactured for us and our carbohydrates to be easily digested.  Herbivores do not compete with humans for food sources; people cannot survive by eating grass or hay.  Omnivores are animals that eat animal and vegetable substances.  Herbivores manufacture their own food from raw materials.  Most herbivores do not require the vitamin supplementation that carnivores need.  A lot of nutritional vitamin products are oversold to the horse and pet herbivore owner.  Mineral supplementation and some vitamins such as A, D & E are required in the diet of a herbivore, if the forage is inadequate in these items.  If the animal has a disease or is fed improperly to develop a secondary nutritional problem, then the underlying cause should be corrected and the animal placed on a proper diet.  If an animal is sick, then probiotics (live bacteria) can also help herbivores and carnivores.  There are also products called prebiotics, which area non-digestible food carbohydrates which can help limit the number of bad bacteria in the colon of monogastric animals (carnivores); we have another handout on probiotics, prebiotics and synbiotics.  With chronic digestive problems altering the diet or removing some foods is the best medicine.  Adult herbivores can manufacture all their own B and K vitamins.  Until their digestive system is developed most immature herbivores cannot live on forages; they usually require milk as their source of nutrition.  Baby ruminants should be considered a monogastric animal their first 6 months of life.  Calves, lambs, kids, foals and other similar herbivores under 3-4 months of age will die on a grass only diet.  Immature ruminants can digests grains but not forages.  This explains why young ruminants can eat a diet high in grain while they are young, then as their rumen matures they can later die from the same high grain diet if the fermentation process is altered (bloat).  For young growing livestock we may recommend alfalfa hay, for adult herbivores we usually recommend grass hay over alfalfa hay, unless they are cattle.  Guinea pigs, rabbits, goats, sheep, llamas and other animals can develop bladder stones from a high calcium and mineral diet.  This can be a medical emergency if the stone does not allow the male patient to urinate.  (Females have a larger urethra and rarely “block up”).

     Cattle, sheep, goats, cervids, camelids, horses, rabbits, birds, hamster and guinea pigs are all herbivores.  Llamas and alpacas are related to camels, while deer and elk are of the cervid family.  Livestock such as cattle, sheep and goats are ruminants; the cervid digestive system is similar to a ruminant.  Ruminants have four stomachs, camelids have 3 stomachs.  For ruminants the forage first goes into the reticulum where metal and other objects can catch in this “honeycomb area”.  The nearby rumen accepts the food for initial digestion and fermentation.  Ruminating or regurgitation of the food for more chewing allows a ruminant to go out and forage, then return to a safe area to further digest their feed.  Ruminating and “chewing the cud” are similar terms.   The third stomach, or abomasum, has many plies of tissue to absorb water from the fermentation vat of the rumen.  The abomasum, or fourth stomach, is the true stomach of the cow, similar to ours.  Both the camelid and ruminant digestive systems are also called forgut fermenters.  The other herbivore species listed above are called hindgut herbivores, and they have only one stomach. 

     The true stomach secretes acids and enzymes to help digest food.  After leaving the stomach the food enters the small intestines, where the digestible food materials are absorbed.  The large intestine absorbs the water before the food enters the rectum.  The “one stomach herbivore animals” do not ferment their food in the foregut (stomach) but instead in the hindgut.  Horses, pocket pets (gerbils to guinea pigs), rabbits and birds are these hindgut fermenters species.  The intestines of a herbivore can be up to 20x the length of the animal.  Herbivores have a longer intestinal tract than the carnivores and omnivores that do not ferment their food as effectively.  Birds, horses, rodents and other hindgut fermenters manufacture and digest their food in the large intestine and the caecum.  The caecum is essentially our appendix, but much larger and more developed.  For this discussion it really does not matter where the food is digested, but to realize herbivores eat plant materials, the plant food is digested and broken up into smaller nutrients, which then feeds a bacterial fermentation process.  The herbivore essentially digests (eats) the bacteria, protozoa, simple sugars, acids and other products from this digestion process.  (When liquor is made we essentially ferment a grain into a nutrient that is more digestible).

     Beware of oversold products for your herbivore animals.  If the hay is green there is enough vitamin A in the forage as a general rule.  A lot of bacterial products are sold to pep up mature horses; a product containing only lactobacillus is such an item.  Lactobacillus is used to make yogurt from milk.  Do adult horses drink milk products?  This example is a little exaggerated as young horses and calves do need this species of bacteria.  Adult herbivore animals under stress and improper feeding can benefit from these cultures, but the removal of the underlying stress should be sought out as the treatment.  Yet the normal population of bacteria needed for each forage may vary.  A probiotics and/or a prebiotic will not prevent a problem if the diet is imbalanced; too much carbohydrates fed at once can cause digestive upsets, especially in herbivores.  Our current knowledge has not been developed enough to thoroughly know the exact bacteria populations needed for every species and every type of diet.  Most of these good bacteria are established naturally in the intestines of herbivores.  It is when we suddenly change feeds that we need to be concerned.  Switching from hay to a grain diet too quickly can lead to enterotoxemia, colic and other severe problems because the feed is improperly digested.  When new foods are introduced to a herbivore it takes a few weeks for the bacterial population to be able to digest the new food.  The bacteria that digest grains are not the same bacteria as the ones who digest hay.  ALWAYS take a few weeks to adjust a herbivore to a new, unrelated food.  If a highly fermentable food, such as a grain, is introduced into a herbivore who does not have the good bacteria established to ferment the grain, the result is an overgrowth of bad bacteria.  These bad bacteria, such as clostridium perfringens, are normally found in small populations within the intestinal tract of animals.  Once the bad bacteria become the main population of the intestines, bloat and colic result.  You may hear that some bad bacteria, such as salmonella and E. Coli, can be removed from the intestines with antibiotics that selectively destroy these gram negative bacteria.  The good bacteria AND the clostridium are gram positive bacteria.  You cannot eliminate all the bad bacteria without destroying all the good bacteria; a process to sterilize the intestinal system is not indicated routinely, unless there is a need to (i.e. a bacterial diarrhea).  Once the good bacteria are gone, the yeast and bad bacteria resistant to the antibiotic used will overpopulate the intestines, possibly causing the patient to die.  Even if you tried to remove all the bad bacteria, within a few days the patient would be exposed to the bad bacteria again from the environment.  The good bacteria normally suppress the bad bacteria.  We have a separate handout on probiotics and prebiotics.

     The most common problems related to herbivore feeding are to give a fermentable diet which the animal is not adjusted to.  As humans we emotionally try to believe that grain is a better food for our pet horses, livestock, rabbits and other herbivores because WE would prefer to eat grain than hay.  Nature has developed their digestive system to the food they found in the wild.  Overuse of supplements and grains are to be avoided to prevent problems.  We feel a complete diet needs to be achieved, but in a manner that is safe for the animal.  Herbivore diets should be consistent in their food type and the frequency of feeding times.  It is hard to believe that a few cups of whole corn can cause colic in a horse, or raisins as treats for chinchillas or gerbils can also upset their digestive system and cause death.  Raisins, garlic, grapes, chocolate are also toxic to dogs and possible other animals, but not people.  Onions are toxic to cats, horses and other animals.  Sheep are unique in that the level of copper and/or copper to molybdenum cannot be high, thus supplements with a high level of copper sold for cattle, pigs, poultry and other species can be toxic to sheep.  Always read the label, as there are some low copper level products which are safe.  Each species is different.  We like to give a variety of treats to our carnivore pets (cats and dogs), which have different digestive systems than a herbivore.  Treats for herbivores should be more consistent with their diet; more fiber than sugar.  Animals are not people, their taste differences are not the same nor do they emotionally care if the food treat is hay, a carrot or if it is a sugar cube, if they like all of these foods.

     When thinking of herbivores and their diet, think of them as a fermentation tank, similar to wine making.  If you suddenly change the diet, the fermentation products and bacteria may be altered (for the worse in some incidences of highly fermentable foods).  


The Staff at the Nelson Road Veterinary Clinic




    There are many other handouts on the various feeds, hay and forages for herbivores from traditional livestock and birds to pocket pets such as guinea pigs.  Poisonous plants, dysbiosis, prebiotics, probiotics are also a consideration with herbivores.