Oat hay is gaining acceptance, especially along the West Coast where alfalfa is so plentiful and grass hays are more scarce.
Oat hay is a grass hay, and its energy/calorie and protein levels are similar to timothy, which averages at around 9% protein. Alfalfa’s protein content is closer to 17%.
The vitamin A level in oat hay is higher than other grass hays. Ten pounds of oat hay per day will fulfill an adult horse’s vitamin A requirements with some to spare.
The phosphorus level in most all hays is about the same, but calcium varies widely from alfalfa’s 56 g/10 lbs. down to oat hay’s 13. A horse’s ideal calcium:phosphorus ratio is about 1.6:1. Oat hay is about 1.3:1.
Magnesium is higher in oat hay than in other grass hays, but when you look at the ratio of calcium to magnesium, which should be 2:1, oat hay comes in at about 1.1:1 because of its low calcium level. Oat hay does contain less potassium than alfalfa and timothy but not enough less to make it of any particular advantage to a horse with HYPP.
On the trace-mineral front, oat hay severely lacks copper, and information isn’t available on oat hay’s selenium and iodine levels.
However, the easiest way to get a good start on correcting oat hay’s mineral problems is to mix it with alfalfa. Feed one pound alfalfa for every five pounds of oat hay. At about 18.5 pounds/day for a 1,000-pound horse at maintenance, the major minerals will be good.
With this mix, ratios of calcium to phosphorus and calcium to magnesium come back into line, at 2:1 and 1.7:1. There’s a little cushion/extra in the magnesium content, but it’s within safe levels and helps balance the high calcium:magnesium ratio in many commercial grain mixes.
Selenium and iodine levels should either be checked through a hay analysis or presumed to be deficient based on trends for your geographical region (consult your local agricultural extension agent) and supplemented at a rate of 1 to 2 mg/day of each, at maintenance.
Oat hay supplies an excessive amount of manganese in the oat-alfalfa hay mixture. Zinc is at NRC-required levels for total amount, but it is too low compared to the manganese level for a proper zinc-to-magnesium ratio.
Copper also remains deficient, despite the boost from the alfalfa. so you’ll need to supplement copper, about 50 mg/day for each 18 pounds of the mixed hays.
Feeding an all-purpose mineral supplement sounds like a good idea, but it may not be enough to fix the copper and zinc deficiencies. It will likely bring the copper up, but it may also elevate the levels of the other trace minerals, making the ratios of these minerals to each incorrect and may even interfere with absorption of the others. We think your best bet is to find separate copper and zinc supplement sources.