Grass or Alfalfa. Timothy or Orchard. Grain hays. Is Bermuda safe? There is plenty of room for confusion in selecting a hay.
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Legume hays, which include Alfalfa, Clover and in some areas Perennial Peanut and Birdsfoot Trefoil, are different from grass and grain hays by being high in protein, very high calcium with proportionally low phosphorus and magnesium and about 30% higher calorie yield.
If feeding Alfalfa as the only hay, the mineral profile is difficult to balance without feeding a large amount of plain grains or brans but can be brought into reasonable balance for an adult horse using those high phosphorus feeds. The mineral ratios are more critical for growing animals. Alfalfa and grain diets are also calorie dense so the horse will have longer periods with nothing to eat unless there is a high work load needing high calories.
The extra calcium is eliminated in urine and forms calcium carbonate crystals. Over time these can accumulate as bladder “sludge” and cause irritation, especially in aged geldings. Formation of actual stones may also result. Excess protein is stripped of its nitrogen and burned for energy. The nitrogen is eliminated in the urine as urea, which bacteria in the environment convert into ammonia. Ammonia in stalls is a potent respiratory tract irritant. The need to eliminate the higher amount of urea also results in a higher urine output.
Alfalfa does have its place. It can be added to diets with poor quality hay to boost low protein or mineral levels. It is also a useful addition to many diets for pregnant, lactating or growing horses which have high protein and calcium requirements.
Nitrate is a compound plants use to manufacture protein but in high levels can be toxic. Nitrate may accumulate in grasses with overfertilization of nitrogen or manure and when grasses are stressed by drought or inadequate nutrients for growth. Some hay types are particularly prone to high nitrate levels and should be avoided if there are options. These include Sorghum, Sudan, Johnsongrass and Pearl Millet.
High levels of simple carbohydrate (sugars, starch) are an issue for horses with insulin resistance and can occur in virtually any type of hay. You always have to analyze to know for sure. That said, more mature cuttings are likely to be lowest while grain hays (oat, barley, rye) tend toward highest levels.
Other countries have problems such as low protein in tropical grasses and several fungal toxins in some regions. Here in North America, the major issue of that type is fungal toxins in Tall Fescue, which can cause problems with pregnancy, birth and lactation.
Otherwise, the quality of grass hays depends more on growing conditions, growth stage and curing conditions during harvest than on the type of hay. Grass hays should be cut in their vegetative stage which means they are still growing and have not started to develop seed heads. Nutrient levels and digestibility are highest at this time. Rapid drying/curing to low moisture levels preserves nutrient levels and avoids issues with molding during storage.
The vast majority of horses will thrive on a high quality grass hay. Adding some alfalfa is beneficial for pregnant, lactating and growing horses which have very high protein and calcium needs. Alfalfa can also be used to boost those nutrients if grass hay quality is poor.
Eleanor Kellon, VMD