Ideally, broodmares should maintain a Body Condition Score (BCS) around 5 to 7 out of 9. Under-nutrition and a BCS less than 4.5 to 5 have been linked to reduced fertility and lower pregnancy rates.
During the last trimester, your mare should be started on a slowly rising plane of nutrition. The ideal diet incorporates good quality, leafy forage along with a commercial concentrate designed for broodmares that contains 12% to 14% protein. Her diet should also contain the proper ratio of calcium and phosphorus and adequate amounts of the trace minerals copper, zinc and manganese to ensure optimal bone development in the fetus. Mares residing in selenium deficient regions of the country (including Eastern Ontario) should receive selenium supplement during late pregnancy to prevent white muscle disease in their unborn foals.
Once she foals, the average mare produces up to 3% of her body weight in milk per day. Because of this substantial output, the postpartum mare requires a steadily rising plane of nutrition and an increased amount of water intake to support her increasing milk production. Peak lactation occurs approximately 6 to 8 weeks after delivery. During this period, a mare requires 1% to 2% of her body weight in good quality, leafy hay daily and a commercial concentrate designed for broodmares. These concentrates typically contain 14% to 16% protein.
Nursing mares should receive a diet containing 0.5% calcium and 0.35% phosphorus and should have free access to fresh water and trace minerals.
An important safeguard during your mare's pregnancy is immunization against Equine Herpesvirus 1 (EHV-1) at the beginning of the 5th, 7th and 9th months of gestation. The EHV-1 strain of Equine Herpesvirus is the leading cause of infectious viral abortions in mares. EHV-1 is typically associated with late-term abortions and the delivery of a well-preserved fetus and outwardly normal placenta. Most horses become infected with EHV-1 during the first year of life. In the majority of cases, the virus becomes latent, just waiting for stress-induced reactivation. Sources of infection for pregnant broodmares include: clinically ill horses shedding the virus in nasal secretions; asymptomatic horses experiencing reactivation of latent infection; or virus laden uterine secretions and placenta/fetus from mares aborting due to EHV-1. All horses in close contact with broodmares - such as barren mares, stallions and teaser stallions - should also be maintained on a rigorous EHV-1 vaccination program. It is important to reduce your pregnant mare's exposure to groups of young horses and any new arrivals that may be shedding EHV-1.
Booster vaccinations 4 to 8 weeks before foaling.
You should booster your pregnant mare 4 to 8 weeks prior to foaling with her regular annual vaccines as decided by you and your veterinarian. This important series of pre-foaling booster vaccinations stimulates the mare to produce high levels of protective antibodies at a time during late pregnancy when she is also producing antibody-rich colostrum. The newborn foal relies on colostrums for absorption of these antibodies during the first 12 to 24 hours of life for protection against a wide variety of viral and bacterial diseases during the early post-natal period.
Deworming your Broodmare
Strategic deworming is another essential aspect of preventive health care. The major gastrointestinal parasites of concern in the mare are large and small strongyles and, in some instances, tapeworms. Another parasite, Strongyloides, can be passed from dam to foal in the milk.
Any deworming program should include active ingredients that are effective against mature parasites and migrating or encysted larvae. In general, it's wise to avoid any unnecessary drug administration, including dewormers, during the first 60 days of pregnancy since this is the time when major organ systems are developing in the fetus.