Feeding The Broodmare: Eating for Two

such as alfalfa or alfalfa grass mix is introduced to the diet as a means of helping the mare maintain condition. But from the ninth month of pregnancy on concentrates will almost certainly be needed in the diet to satisfy increased energy and protein requirements during the final trimester and to combat other factors that tend to arise at this time and threaten her with weight loss. Protein needs increase from 8 percent crude protein in early and midgestation to 10 percent in the ninth month and 11 percent in the 11th month energy requirements increase by about 20 percent from those of early pregnancy.
Another challenge to the broodmares ability to maintain condition during late gestation is the fact that the fetal foal as it begins to grow more rapidly will increasingly compress the mares digestive tract causing her appetite to decrease at a time when she most needs the nutrients from the food she consumes. Smaller meals fed with greater frequency can help keep her feed intake steady because they wont overfill the mares digestive system making her uncomfortable. 
The quality of the feed and its effect on broodmare diet should be taken into consideration. Broodmares typically enter the final trimester during the winter months when available forage tends to be of lower quality. Good quality forage should be the basis of all feeding programs but it is especially important when the mares diet is supplying nutrients to the fetal foal as well as to her own body.
A body condition score that remains within the optimal range of 5 and 7 is usually a good indication that a broodmares energy and protein requirements are being met by her feeding program but it doesnt necessarily mean that all of her nutrient needs are being satisfied. Deficiency in certain minerals and vitamins may not be reflected in the mares appearance.
The most crucial macrominerals in a broodmares diet are calcium phosphorus and magnesium. Calcium and phosphorus in particular are critical to the healthy development of the fetus. In the final trimester an 85 percent increase in the amount of calcium and a 100 percent increase in the amount of phosphorus in the mares diet are recommended to meet the fetal foals increased uptake of these minerals in late gestation. Phosphorus deficiencies are more common in late pregnancy while calcium deficiencies are more likely to occur during lactation.
Trace minerals copper zinc manganese iron