Horses are non-ruminant herbivores (hind-gut fermentors). Their small stomach only has a capacity of 2 to 4 gallons for an average-sized 1000 lb. horse. This limits the amount of feed a horse can take in at one time. Equids have evolved as grazers that spend about 16 hours a day grazing pasture grasses. The stomach serves to secrete hydrochloric acid (HCl) and pepsin to begin the breakdown of food that enters the stomach. Horses are unable to regurgitate food, so if they overeat or eat something poisonous vomiting is not an option.
Horses are also unique in that they do not have a gall bladder. This makes high fat diets hard to digest and utilize. Horses can digest up to 20% fat in their diet, but it takes a span of 3 to 4 weeks for them to adjust. Normal horse rations contain only 3 to 4% fat.
The horse's small intestine is 50 to 70 feet long and holds 10 to 23 gallons. Most of the nutrients (protein, some carbohydrates and fat) are digested in the small intestine. Most of the vitamins and minerals are also absorbed here.
Most liquids are passed to the cecum, which is 3 to 4 feet long and holds 7 to 8 gallons. Detoxification of toxic substances occurs in the cecum. It also contains bacteria and protozoa that pass the small intestine to digest fiber and any soluble carbohydrates.
The large colon, small colon, and rectum make up the large intestine. The large colon is 10 to 12 feet long, and holds 14 to 16 gallons. It consists of four parts: right ventral colon, sternal flexure to left ventral colon, pelvic flexure to left dorsal colon, and diaphragmatic flexure to the right dorsal colon. The sternal and diaphragmatic flexures are a common place for impaction. The small colon leads to the rectum. It is 10 feet long and holds only 5 gallons of material.
Read the feed labels
You must read the labels when purchasing feed. By law the ingredients are listed in order, starting with the most abundant. If the first ingredient listed is a type of forage product, then you are buying a complete feed (mostly hay in a bag).
The biggest misconception I come across in people feeding thin horses for weight gain is the use of a complete bagged feed such as Equine Senior. This is great for older horses with poor dental health that have difficulty in chewing or digesting hay. Another option is to buy alfalfa cubes or pellets and add in grain for weight gain or to get away from hay dust allergens.
Equine Senior is 14% Crude Protein and 5.5% Fat. In order for a 1,000 pound horse to gain weight as this being the sole ration, you will need to feed approximately 20 pounds per day.
If the first ingredient is a grain product this will indicate that this is a more potent feed source and will require feeding smaller volumes such as sweet feeds.
Sweet feeds vary from around 12-32% Crude Protein and 5-12% Fat. Suggested amount for a 1,000 pound horse is usually around 2-7 pounds per day.
Other feeds to increase weight gain include: dried beet pulp, can be fed up to 6-8 pounds per day. Corn oil, starting with _ cup 2x/day and can gradually work up to 1 cup 2x/day. There are many over the counter weight supplements to choose from. May also switch from grass hay to more alfalfa in the diet.
There are many ways to promote weight gain for your horse. You do not have to use every above mentioned ingredient, just choose what is most economical and practical for you. Since all horses are not created equal, consult with your veterinarian as to what would be best for your horse.
1. Forage is the base! Always try to feed the most forage possible then add concentrate.
2. Feed at a rate of 1.5 to 2% of the horse's body weight (1000 lb. horse = 20 lbs.).
3. Feed by weight not volume! A 1 lb. scoop of oats does not equal 1 lb. of corn.
4. Stomachs are small so concentrates, if used, should be fed twice a day if not more with no more than 0.5% body weight per feeding.
5. To maintain body weight, most horses need only good forage, water, and a mineral block.
6. Store feed properly: it should be kept free of mold, rodents, or contamination.
7. Keep Ca:P ratios around 2 parts Ca to 1 part P.
8. Feed on a set schedule (horses are creatures of habit and are easily upset by changes in routine).
9. Change feeds gradually over 7-10 days (horses' stomachs cannot cope with drastic changes in feed; could cause colic).
10. When work or exercise decreases, decrease the grain.
11. Be aware of the pecking order in your horse's pen- are they getting their feed?
12. Examine teeth at least once a year to make sure they are able to chew feed properly.
Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or firstname.lastname@example.org.