The ideal calcium to phosphorus ratio for horses is 2:1. Most clovers and medics (including lucerne) have ratios in excess of 2:1. Most grasses have calcium to phosphorus ratios of 1:1. However, the lusher a grass is the lower the calcium to phosphorus ratio.
In some cases the ratio may be 0.8:1. Pastures that are over-fertilised with effluent run-off and are very lush can be a problem. Including grasses, clovers and medics in the pasture mix will overcome this problem.
Horses grazing some tropical grasses for extended periods can suffer `Big Head’ disease or Osteodystrophia fibrosa. These grasses are buffel grass, green panic, setaria, kikuyu, guinea grass, para grass, pangola grass and signal grass. The cause of the problem is a high level of oxalates.
Calcium oxalate is insoluble and unavailable to the horse. There needs to be more calcium than oxalate in the pasture for the calcium to be available. Oaten chaff has 0.11 percent calcium with 0.08 percent oxalate and 100 percent of the oaten chaff calcium is available. However, Narok setaria has 0.27 percent calcium and 1.6 percent oxalate.
It has a calcium to oxalate ratio of 0.1:3. Because oxalate dominates, it means none of the calcium is available to the horse. Mineral supplement mixtures that provide the required amount of calcium to phosphorus should be made available to horses grazing setaria, buffel and kikuyu pastures.
Good mixtures are 1 kilogram of rock phosphate mixed with 1.5 kilograms of molasses or 1 kilogram of a mixture of 1.33 kilograms of ground limestone and 0.66 kilograms of dicalcium phosphate mixed with 1.5 kilograms of molasses. Alternatively, supplement with a feed that is a good source of calcium such as lucerne hay.
Fodder crops:
Fodder crops are usually grown in rotation with pastures providing feed when pastures are not actively growing.
Winter:
For winter feed the most acceptable or preferred crops in order are triticale, barley, ryegrass and oats. Horse breeders have accepted for many years that barley was the most acceptable but recent observations at Hawkesbury Agricultural College indicate that triticale is the most acceptable.
Saia oats, one of the most productive oats, is totally unacceptable to horses until it goes to seed. The horses will then selectively eat the seedheads. Berseem clover, a winter/spring growing legume, has been sown with ryegrass as a pasture.
In the County of Cumberland it is gown as a winter forage crop for horses; baled wet it is fed to thoroughbred racehorses in work at the major racetracks in Sydney.
Summer:
Summer feed has often been a problem on breeding stud farms. Farmers have experimented with various crops with little success. The most common summer forage crops are shirohie and japanese millet, pearl millets, hybrid millets, hybrid forage sorghums and sudan grass. They grow actively from November to March.
Horses do not like grazing the millets, hybrid sorghums and sudan grass. They prefer to graze summer grasses that might be growing in the paddock. The millets have an advantage over the hybrid sorghums and sudan grasses in that they do not cause prussic acid poisoning.
The hybrid Sudan grasses are the best sorghum, sudan grass options because they have lower prussic acid and thinner stems with more leaf. Always check with the seed company for recommended grazing and cutting heights.
In areas of south-western United States, forage sorghums are reported to cause an increasing number of cases of `Cystitis syndrome’ in horses. The condition causes irritation of the urethra and vagina in the mare, and of the urethra in the stallion and gelding. Another symptom is muscular incoordination in the rear quarters. So far as is known, sudan grass hay, if properly cured, may be used without danger.
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