Nutrition for Pregnant Mares Throughout Gestation

I have just purchased a QH mare who is due to foal the first part of March. As this is our first foal, what if any supplements would you recommend for the mare at this point in her pregnancy. I am an OB-Gyn Nurse Practitioner and know how important adequate quality intake is for both. Thanks, DH, Texas

Dear DH,

Since the average length of pregnancy in the mare is 338 – 343 days or about 11 months, your mare is heading into her last trimester. Up to now, she has done just fine on the same nutritional program you would use for any horse: a complete and balanced diet fed at a rate of 1 – 2% of her body weight daily based on high-quality forage. Of course, fresh water and loose salt is always available. But during the last four months of gestation the foal grows rapidly, requiring the mare’s diet to change in three key areas: energy, protein and vitamins/minerals.

A pregnant mare’s energy requirements gradually increase after the seventh month of gestation, so you should gradually begin to supply her with more calories. Of course, if she’s already overweight, then this step may not be necessary. Aim to keep her in good flesh but not too heavy (between a 5 and a 6 on the Henneke Body Condition Scoring scale, where 1 = emaciated and 9 = obese). It may be tempting to just add an extra scoop of grain to her ration, but fat or beet pulp are safer sources of calories.

Adult horses in maintenance as well as mares in early gestation only need an 8% crude protein diet. But during the last trimester when the foal is building lots of tissue, that level will need to be upped to 10 – 12%. Instead of simply increasing the amount of grain in the diet, which can lead to problems, begin swapping out flakes of grass hay for flakes of alfalfa hay, which are higher in protein.

Feeding alfalfa hay also provides the additional calcium that mares need in late gestation. Other minerals of interest include selenium–especially if you are in a selenium-deficient area of the country–and copper, which may have a protective effect against developmental orthopedic diseases such as osteochondritis dissecans or OCD. Also, make sure your mare gets plenty of Vitamins A and E particularly if she does not have access to fresh grass. A multi-vitamin/mineral supplement  made especially for mares may be a good choice now.

One final bit of advice: during the last trimester the foal takes up quite of bit of room in the mare’s abdomen. Just when she should be eating more there’s no room for food! Try to feed smaller meals more frequently so she takes in the nutrition she needs without becoming uncomfortable. Now just work with your veterinarian to make sure your mare’s other health needs are met (deworming, vaccination, hoof and dental care) then provide careful monitoring until the Big Day!