Hay is just dried grass but there are several things to consider when making the transition from pasture to hay.
Typical Fall Pasture with Grasses Going Dormant
As grasses mature and develop their seed heads, fiber fractions progressively increase while more easily digested carbohydrates, protein and even minerals drop. The horse can compensate for a while by concentrating on grass that is still green and eating more but eventually the quality of the pasture becomes more like straw and the horse’s condition obviously suffers. You want to step in before that point.
Begin offering hay when grass growth has stopped and areas are turning brown. Unless the hay was baled off fields being grazed, it is a diet change and should be made gradually.
Hay is basically “grass jerky” and much lower in moisture. To keep intestinal contents flowing easily and facilitate digestion and fermentation, water consumption will have to increase substantially. Try to keep hay feeding areas close to water supplies and make sure salt is freely available. You can also sprinkle salt onto moistened hay to help guarantee intake. Use 1 oz (2 tablespoons) per horse.
Hay has other key nutritional differences besides lower water content. Omega-3 fatty acids comprise 50% of the fat content in fresh grass and are lost very rapidly when hay is cured and stored. This omega-3 shortage is exacerbated by the fact all other feed ingredients in the equine diet are also low in omega-3 and high omega-6. To boost omega-3 intake, feed flax seed, 2 to 8 oz/day.
Other major losses when grass is cured include vitamins C and E. The horse can manufacture vitamin C and never develops full blown vitamin C deficiency but levels may not be optimal for health off pasture. This is especially so for exercising horses and horses with allergic or lung disease. Supplementation with 3 to 5 grams/day of vitamin C is reasonable.
Vitamin E is a key antioxidant for protecting cell and organelle membranes throughout the body. It is particularly important in the nervous system, muscles and immune system. Minimum recommended intake is 1 IU/lb of body weight which can be increased to 2 IU/lb for exercising horses and immune system support.
Careful attention to nutrients missing from hay can help keep the bloom on your horse when they come off pasture.
Eleanor Kellon, VMD