What Is the Best Feed for a Pregnant Mare? A Complete 6-Step Canadian Guide

What is the best feed for a pregnant mare? The short answer: a fortified, broodmare-specific concentrate combined with quality grass hay, with the amount and nutrient density adjusted by trimester light through month eight, then increasing through the final trimester to support rapid fetal growth.

Most of the mistakes broodmare owners make come from treating pregnancy as one continuous nutritional state rather than a process that changes dramatically over eleven months.

This guide gives you a complete 6-step framework, covering hay, calcium and phosphorus, omega-3s, vitamin E, and exactly what to avoid, so you can feed your mare with confidence from confirmation to foaling.

Six Steps to Feeding a Pregnant Mare

Here is the complete framework feed recommendations for pregnant mare programs are built around, broken into six practical steps:

Step 1 - Feed at Maintenance Through Month 4

Except for a modest increase in vitamin A and vitamin E, pregnant mares can be fed to meet their normal maintenance requirements through the first four months of gestation. Good-quality pasture or hay, roughly 1.5 to 2% of body weight, meets virtually all of her needs during this stage. No special concentrate is required yet.

Step 2 - Begin Increasing Nutrition at Month 5

Research from the National Research Council shows that nutrient requirements increase starting at month 5 of gestation, earlier than the month-8 mark traditionally assumed.

 From this point, energy needs rise by roughly 0.5 to 1 Mcal of digestible energy per day through month 11, alongside increasing protein, calcium, and phosphorus needs.

Step 3 - Switch to a Fortified Broodmare Concentrate

By month 5, plain hay and pasture generally cannot supply the elevated protein, calcium, phosphorus, copper, and zinc your mare now needs.

This is where a broodmare-specific concentrate becomes essential. Our Hi-Pro Step 1 - Start Right is formulated specifically for mares in late gestation and lactation, soy-free, highly digestible, and fortified with the exact minerals broodmares need most.

Step 4 - Maximize Forage Quality, Not Just Quantity

Forage should remain the foundation of the diet throughout pregnancy, typically 10 to 12 kg per day for a 500 kg mare.

As nutritional demands rise, upgrading to a richer hay, such as a timothy/alfalfa mix, often does more good than simply feeding more of a lower-quality hay. See our Timothy Hay vs Alfalfa Hay for Horses guide for how to choose the right forage for a broodmare's elevated needs.

Step 5 - Balance Calcium and Phosphorus Precisely

Calcium and phosphorus needs roughly double by late gestation. Getting the ratio right, not just the total amount, is critical (covered in detail below).

Step 6 - Monitor Body Condition Monthly and Adjust

Mares typically gain 9 to 16% of their starting body weight over the full pregnancy, with 65 to 75% of that gain occurring in the final three months. Check body condition score monthly and adjust feed accordingly. Overnutrition is actually more common than undernutrition in well-cared-for broodmares, so resist the urge to simply feed more to be safe.

How Much Hay Should a Pregnant Mare Eat?

Forage is the most important part of a broodmare's diet and should meet the majority of her energy and protein needs in early-to-mid gestation when fed in adequate amounts. For a 500 kg mare, that works out to roughly 10 to 12 kg of hay per day.

For a complete breakdown of daily hay needs by body weight and life stage, read: How Much Hay Does a Horse Eat in a Day?.

As pregnancy advances and her stomach capacity becomes physically limited by the growing foal, splitting her daily ration into 3 or more smaller meals rather than 1 to 2 large feedings improves digestive efficiency and reduces colic risk.

Should I Feed Alfalfa to Pregnant Mares?

Feeding alfalfa hay during late gestation can help provide the additional calcium a mare needs that pure grass hay often cannot supply on its own.

Many broodmare programs use a grass/alfalfa mix specifically for this reason, getting the benefit of alfalfa's calcium and protein while keeping overall energy density manageable.

The caution: alfalfa is not automatically appropriate for every mare. Easy keepers, mares prone to weight gain, or mares with metabolic concerns should be monitored closely if alfalfa is introduced. Work with your vet to confirm the right ratio for your mare's body condition.

Why Do Pregnant Mares Need Calcium and Phosphorus?

During the last 90 days of pregnancy, research-based guidelines call for roughly 0.45% calcium and 0.35% phosphorus in the total diet, compared to about 0.3% calcium and 0.2% phosphorus during early gestation maintenance. That is nearly double the requirement by the final trimester.

Just as important as the total amount is the ratio between the two. Calcium and phosphorus should ideally sit at roughly a 2:1 ratio.

Failing to provide this balance correctly means the mare draws these minerals from her own skeleton, leading to bone demineralization in the mare alongside reduced milk

 production after foaling. Vitamin D also plays a supporting role here, as it improves the body's ability to actually utilize and absorb dietary calcium and phosphorus.

Do Omega-3s Benefit Pregnant Mares?

Omega-3 fatty acids are considered important for fetal development and colostrum antibody transfer. One specific omega-3, DHA, docosahexaenoic acid, found in marine-based sources, has been linked to improved foal learning and memory performance when mares were supplemented through the last three months of pregnancy into early lactation.

Linseed (flax) meal is a practical and widely available omega-3 source for Canadian broodmare owners and can be a beneficial addition during late gestation and early lactation.

Do Pregnant Mares Need Vitamin E?

Adding 1,200 to 2,000 IU of natural vitamin E to a mare's ration during the last trimester has been shown to help increase the concentration of immunoglobulins in colostrum, directly boosting the passive immunity her foal receives at birth.

Fresh grass naturally provides vitamin E, but Alberta mares fed conserved hay through winter months, which is most of the year here, typically need vitamin E supplied through a fortified concentrate or balancer, since vitamin E degrades significantly in stored forage over time.

What Not to Feed a Pregnant Mare?

Beyond general feeding mistakes, several specific feeds and conditions carry real risk during pregnancy:

•        Endophyte-infected tall fescue - this is the single most well-documented dietary danger for broodmares. The endophyte fungus causes fescue toxicosis: prolonged gestation, thickened placenta, agalactia (no milk production), and significantly increased risk of foal death. If your hay or pasture contains tall fescue, have it tested for endophyte before feeding to a pregnant mare

•        Moldy or dusty hay - mycotoxins in moldy hay are linked to abortion risk. Never feed hay you would not be comfortable eating yourself; smell-test every bale before feeding a broodmare

•        Excess grain or high-starch concentrates - large starchy meals increase colic risk and can contribute to excessive, rapid weight gain that is not healthy for mare or foal

•        Unverified herbal supplements - herbs like fenugreek and many natural blends have not been safety-tested in pregnant mares; only use supplements cleared by your veterinarian

•        Sudden feed changes close to foaling - any diet change should be introduced gradually and avoided entirely within the final two weeks before foaling, to prevent gastrointestinal upset at the worst possible time

Pregnant Mare Nutrition by Trimester

Stage	Crude Protein	Calcium / Phosphorus	Key Focus
Months 1-4	~8%	0.3% Ca / 0.2% P	Maintenance feed, hay/pasture sufficient
Months 5-8	~10%	Gradually increasing	Begin transition to fortified concentrate
Final Trimester (9-11)	~10-12%	0.45% Ca / 0.35% P	Broodmare feed + vitamin E + omega-3
Lactation (post-foaling)	14%+	0.6% Ca / 0.4% P	Highest demand - energy, Ca/P roughly double

 

These are general research-based guidelines; every mare and every hay lot differs. A forage analysis is the only way to know exactly what your specific hay is providing and what gaps a concentrate needs to fill. Read our guide: Low-Sugar Hay for Horses: What Canadian Owners Should Know to understand why every hay batch is different and why testing matters.

Feed Your Broodmare With Confidence - Horse Creek Hay & Feed

What is the best feed for a pregnant mare? It is not one single product, it is the right combination of quality forage and a fortified concentrate, adjusted as her needs change across eleven months.

Feed at maintenance through month four, transition gradually starting at month five, prioritize calcium-phosphorus balance and vitamin E in the final trimester, and always avoid moldy hay and endophyte-infected fescue.

At Horse Creek Hay & Feed in Rocky View County, we carry Hi-Pro Step 1 - Start Right, formulated specifically for broodmares and foals, alongside Alberta-grown timothy and timothy/alfalfa mix hay with full nutritional analysis on every bale. Knowing exactly what is in your hay matters more during pregnancy than at almost any other life stage, and we make sure you never have to guess.