Doctors Corner – Feb 04

Preparation for Foaling
R. Paul Schwab, D.V.M.
Kulshan Veterinary Hospital

By now most pregnant mares in this area are in the last trimester of pregnancy or may already have a foal on the ground. This article will discuss some of the health concerns and management decisions needed to help insure the delivery of a healthy foal.

The last few months of the mare’s gestation is very important from a nutrition standpoint. A 1200 lb. mare may gain 175-225 lbs. during a typical gestation, most of which is during the last 3 months. Most mares should eat anywhere from 2.25-2.5% of their body weight per day in feed with the bulk of this diet consisting of good quality forage. Protein levels in the mare’s ration should be around 12-14%. Careful monitoring of body condition during this time is crucial. Just because a mare is round doesn’t mean she is fat. It’s important to look at multiple parameters when evaluating body condition including ribs, tail head fat, and cover along the top line of the back. The use of the Henneke body condition scoring system is helpful. Ideally the mare should be moderately fleshy to fleshy.

Another aspect of nutrition that is very important to the late gestation mare is mineral balance, especially pertaining to calcium and phosphorus. The ideal ratio of calcium to phosphorus is 1.2:1 to 1.5:1. Concerns with ratios much higher than this are with developmental orthopedic diseases in the foal such as osteochondritis and limb deformities. Mineral imbalances can also be responsible for problems such as retained placental. To put this in perspective, alfalfa hay can have a ratio of calcium to phosphorus of 5:1. On a pure alfalfa diet, the mare would be getting far too much calcium compared to phosphorus. Mares on a high alfalfa diet should be getting a grain with a high phosphorus content to balance it out. Also vitamin mineral supplements can help balance out the ration. Forage or hay analysis can help your veterinarian or nutritionist look for deficiencies or excesses in the ration.

Vaccinating the mare before and during pregnancy is critical not only for the mare but also for the survival of the foal. This is especially true for mares on large farms with exposure to many diseases and other horses. Rhinopneumonitis vaccination is recommended in most situations because it protects the mare from aborting the foal. Because of it’s short-lived immunity, Rhinopneumonitis vaccine must be given at 5, 7, and 9 months of gestation. It is also recommended to use a Rhinopneumonitis vaccine that is labeled for use in the pregnant mare for preventing abortion.

To protect the foal after birth, the mare should be given vaccinations recommended by your veterinarian for your area about 4 weeks before foaling. In our area that would include Influenza, Rhinopneumonitis, Tetanus, West Nile, and usually Encephalomyelitis (Eastern and Western). If the vaccination history of the mare is unknown, primary and secondary boosters should be given at least 4 weeks before the foal is born. If these guidelines are followed, the colostrum of the mare should have high levels of antibodies to these diseases. Other vaccinations to consider depending on your situation may be Botulism, Rotavirus, and Rabies. As a side note, when giving influenza vaccinations to the mare during the last month of gestation, it is important to use the intramuscular vaccine and not the intranasal vaccine. Although the intranasal vaccine works very well for most horses, it does not stimulate the proper antibodies that go into the colostrum for the foal.

By the last trimester most mares have been palpated for pregnancy by your veterinarian and may not need to be seen again, especially if you give your own vaccinations to your horses. However, a veterinary visit during the last 2-3 months may be beneficial to look at the body condition of the mare, examine for any problems, and make sure she is still pregnant, especially if the only pregnancy exam was done very early. Also if your mare has had a Caslick’s procedure done on her in the past, it will need to be removed during the last 2-3 weeks. (A Caslick’s surgery is the suturing of a portion of the vulva to prevent uterine infection in some mares, especially thoroughbreds from the track). This time may be useful to discuss the foaling procedure itself, abnormalities with foaling, and early postpartum concerns with the mare and foal. Other reasons to call your veterinarian include abnormal vaginal discharge or premature udder development. Early intervention and monitoring of high-risk mares can help them carry their foals to term.