Mineral requirements of growing horses

The mineral requirements of weanlings have received some attention in recent years. but much more work is needed. Calcium is oi concern because of its need for bone formation but also because excessive amounts can decrease utilization oi other minerals, The calcium to phosphorus ratio must also be considered. A range of ratios of 1:1 to 3.1 seems to be reasonable. The National Research Council (NRC, 1989) suggested that growing horses, 4 to 12 months old with a mature weight of 500 kg,would need 29-36 g of calcium daily. Some authors have suggested that NRC calcium values are too low whereas some have suggested NRC are too high. It is concluded that at this time there is not sufficient evidence to significantly change the NRC calcium requirements. The biggest range in recommendations is probably for copper and zinc. The NRC(1989) recommended dietary concentrations of 10 and 40 mg/kg of dry matter, respectively. Others have suggested that much higher copper and zinc concentrations are needed to prevent osteochondrosis. Reasons for differences among experimental results need to be determined.