Feeding Mares During Late Pregnancy by Dr John Kohnke

A balanced adequate ration
Most mares in Australia are bred in the spring to midsummer period when mares cycle more frequently and fertility is at its optimum. This means that most mares, allowing for their 11 month period of pregnancy, are in the last trimester of pregnancy (last 3 months or 8-11 month of pregnancy) in the mid winter to mid spring season.

Early foaling mares therefore pass through their last 3 month of pregnancy during the colder winter months, often with less available pasture and hence energy, protein and mineral intake, unless they are supplemented with hard feed, hay and calcium and phosphorus and a range of trace-minerals to make up shortfalls in their diet.

Nutritional needs of late pregnancy
Studies have shown that the unborn foal must be able to receive adequate energy, protein, bone minerals, trace-minerals and vitamins through the placenta to fuel its rapid growth of doubling its weight and a 47% gain in size during the last trimester of pregnancy.

The young foal also needs to store reserves of calcium, copper, zinc, iron and vitamin A in its liver to supplement the relatively low level in mare’s milk during early lactation after foaling.

Many grass based pastures are unable to provide adequate bone minerals and soil deficiencies of trace-minerals including copper, zinc, manganese, selenium and iodine are widespread in the major horse raising areas in Australia.