If you find yourself caring for a new resident mare who is pregnant or lactating (which hopefully should not be a frequent occurrence! Check out Why Residents Shouldn’t Breed At A Farmed Animal Sanctuary for more), you will find they have different nutritional requirements than nonpregnant residents. This resource is meant to provide a brief introduction to the nutritional requirements of pregnant and lactating mare residents. If you haven’t read it, we recommend looking at “Daily Diet, Treats, And Supplements For Horses” before reading this resource. In that resource, we learned a bit about how a horse’s digestive system works and discussed the building blocks of the dietary needs of horse residents. The types and amounts of these building blocks necessary change throughout a mare’s pregnancy and lactation. While it may seem like a lot to take in, we will break it down into stages of pregnancy and lactation, making it easier to navigate as you care for your resident through this time. Ultimately, this resource seeks to provide caregivers with a foundational understanding of nutritional requirements they can use when they speak with an experienced veterinarian or equine nutritionist about appropriate diets for pregnant or lactating mare residents.

Elective Termination of Pregnancy
If an incoming resident is early on in their pregnancy, some sanctuaries choose to induce miscarriage. Sanctuaries interested in seeking this treatment should speak to their veterinarian about the off-labelThis term is often used to describe extra-label drug use. This means that a drug is used in a way other than what is described on the label or package insert. If a drug is used in a different species than what it has been approved for, this is extra-label use. Other examples include using a drug to treat a different condition than it is approved for or administering it in a different way than the directions describe. Extra-label drug use can only occur within the confines of a valid veterinarian-client-patient relationship. use of Lutalyse and Estrumate for this purpose or if another treatment is recommended. Sanctuaries should not perform this treatment themselves unless directed by a veterinarian. The decision to induce miscarriage ultimately depends on an individual sanctuary’s Philosophy of Care.  

One Size Doesn’t Fit All
This is not one size fits all. Every horse is an individual and requires individually designed diets, depending on various factors. Easy keeper mares  (those who gain weight easily) may require less in their diet than others who struggle to keep weight on or lactate heavily. Health status comes into play as well. While different factors tend to align with specific generalized needs, you should always consider each resident individually. This resource cannot account for individual differences but provides information on some of the general considerations given to pregnant and lactating mares’ diets. 

Special Considerations For Pregnant And Lactating Mares

If you are caring for pregnant and lactating mare residents at your sanctuary, there are several dietary adjustments you might consider, depending on their stage of pregnancy or lactation.  If you recall from our basic nutrition resource, an average healthy adult horse will consume 1.5%-2.5% of their weight each day. Forage quality and type will affect the nutritional value a horse receives. A horse may require supplemental grains or vitamin and mineral supplementation based on those levels. For this reason, it is recommended that the forage growing in their pasture and the hay purchased for their diet be tested for nutritional value to allow you and your veterinarian and/or equine nutritionist to develop the best diet plans for resident horses. This can be especially important in ensuring pregnant and lactating mare residents stay healthy.

*To maintain a healthy horse’s weight and nutritional intake, it is essential to know:

1. How much they weigh (approximately),

2. How much a horse consumes daily (1.5%-2.5% of their body weight), and

3. The nutritional value of the forage is provided.

Overall, a mare will gain between 9-16% of their original weight during pregnancy, which comprises the placenta, fluid, and fetus. The majority of this weight gain, around 65-75% or more, will occur in the final three months of pregnancy, significantly affecting the nutritional requirements of the pregnant resident. During this time, they will require more protein and nearly twice the phosphorus and calcium they usually intake! They need adequate amounts of minerals, vitamins, and amino acids to grow tissues, cartilage, and bone. Their energy needs may increase by up to 20% during this time though it can be lower than this. Their needs in early to mid-pregnancy will look much different, as we will cover.

Make Changes to diet slowly 
Changing a resident’s diet too quickly can result in serious health issues. In horses, abrupt diet shifts change their microbiome and can cause digestive issues. It also puts the resident at risk of developing colic or laminitis, which are serious health concerns. Slowly switch the food, starting with a small amount of the new food mixed with the old, and adjust the ratio of old to a new food until they are eating all the new food. 

Nutritional Components

Mare Nutrition Affects Fetal Development And Foal Health
Deficiencies in certain nutrients can lead to poor foal growth or the development of health issues later. Numerous studies have been conducted on mare nutrition and its effects on fetal development and foal health. Deficiencies or overfeeding the mare can also have a detrimental impact on the foal. This is one reason why it is vital to consult with an equine nutritionist or an experienced veterinarian.

Carbohydrates (Specifically Fiber): It probably doesn’t surprise you that carbohydrates are generally the biggest part of a horse resident’s diet. Carbohydrates can be broken down into fiber, starch, and sugars. Lots of fiber (hay and grass) is integral to a horse’s diet. Beneficial microorganisms in a horse’s hindgut can break down all that structural fiber and turn it into an excellent energy source. As you may imagine, a pregnant or lactating mare must increase her energy intake during certain stages and decrease it during others. Later-stage pregnancy and early lactation will see a significant increase in nutritional requirements.

Because of the importance of structural carbohydrates (forage) in a horse’s diet, it is vital that the quality of the carbohydrates (forage) be monitored closely. Dusty and moldy hay isn’t a good choice. Ideally, good quality hay is one that has been cut at the right stage and proper length. Low-quality hay that is too “stemmy” or even too fine can cause digestive issues such as impactions. Hay that is cut too late has lost most of its nutritional value, as it has an increase in lignin (the thing that makes stems tougher), which can’t be digested.

Read more about forage for horses here.

Protein: Proteins are vital as they provide essential and nonessential amino acids. Horses, in particular, require the essential amino acid lysine. How much of these amino acids an individual horse needs depends mainly on their age and whether they are pregnant or lactating. A healthy neutered or spayed adult requires less protein (and corresponding amino acids) than growing or pregnant or lactating individuals.

Depending on the stage, pregnant or lactating horses require higher amounts of protein, between 12 and 18 percent. During later stages of fetal development, requirements for protein will increase significantly. While forage is a source of protein, some mares may require concentrates or balancer pellets to meet the demands of their body. Legume hays, such as alfalfa and clover, are generally higher in protein than grass hay, such as timothy or bermudagrass. Good quality legume hay can have roughly 18 to 22 percent crude protein, while good quality grass hay can have 10 to 16 percent crude protein. Again, the quality and growth stage at harvest determines how digestible the hay is and influences how much protein the horse receives from it.

Fat: Generally speaking, horses don’t require much fat in their diet though a lactating horse may have slightly higher requirements. Did you know that horses don’t have gallbladders? This means it is difficult for them to digest large amounts of fats. Generally, 3-4 percent fat in food is a good amount for horse residents. Too much more can lead to unnecessary weight gain and potentially cause health issues. Consult with your veterinarian or nutritionist about the proper amount of fat in a lactating resident’s diet.

Vitamins: Did you know horses actually produce some of the vitamins they need during the digestive process (vitamins B and K)? Most other required vitamins are accessible in green, leafy forage. However, if they don’t have access to a lot of quality forage or have particular health needs, such as pregnancy and lactation, they may benefit from the supplementation of these vitamins. It is common for pregnant and lactating horses to receive a balancer pellet or other such supplementation, specifically in later pregnancy/early lactation. It is best to discuss whether a resident would benefit from any vitamin supplementation with your equine veterinarian.

As long as residents have access to the outdoors, where they can soak up the sun, their vitamin D needs are usually met. Forage also contains some amounts of vitamin D.  Horses get vitamin A from eating fresh grass and good-quality hay. Horses on a regular diet usually have adequate stores of all the B complex vitamins and vitamin K. As for vitamin C, horses can produce this in their liver from glucose. Vitamin E is also found in grass, fresher hay, and legumes. During pregnancy and lactation, your veterinarian or equine nutritionist may recommend additional vitamin E supplementation.

Minerals: Many minerals can be beneficial for a horse, but there are three that are of particular importance: calcium, phosphorus, and salt. There are many other minerals that are necessary for happy, healthy horses. For pregnant and lactating horses, specifically, those in the later stages of pregnancy or early stages of lactation, minerals like copper, selenium, iodine, and zinc are essential for the mother’s health and healthy fetal development and milk production.

The amount and ratio of minerals are essential things to consider when developing a diet plan for a resident. Individuals may require more particular minerals during periods of growth and pregnancy. Your veterinarian or equine nutritionist will help you balance the need for minerals (and other nutritional requirements) between forage, concentrates, and supplementations.

Early To Mid Pregnancy 

Some sources say that, during early pregnancy, a healthy resident will often meet their requirements from quality forage and pasture (Around 15 lbs for a 1,000-1,200 pound horse) and won’t require any additional food or supplementation. However, more recently, sources say energy and protein requirements may increase to around 10% during this time, so keep a close eye on them for any changes and discuss this with your veterinarian. Mineral supplementation may also be recommended, and a trace mineral salt block should be readily available. More recent studies highlight the importance of specific nutrients for early fetal development. They should be discussed with an equine nutritionist or experienced veterinarian to prevent any potential issues with foal development. At this time, their diet should generally consist of 8% crude protein as well as 0.2% phosphorus and 0.3% calcium. The nutritional needs of a resident may increase around 5 months into the pregnancy though high-quality pasture and forage can often fulfill much of their energy needs though they may require small amounts of concentrates for energy or a balancer ration (around 1 to 2lbs) to ensure they have all the minerals they require. 

Avoid Fescue Grasses!
While fescue grass is generally a good forage source, it can be problematic during pregnancy/lactation. Fescue can contain a fungus called endophyte that can be particularly harmful to mares and newborn foals. It can affect milk production and has even been connected with death in foals. You can have it tested for fungus, but it is better to be safe than sorry. It is a good idea not to feed fescue or allow them access to fescue in the last few months of pregnancy.

Late Pregnancy (9-11 months)

As mentioned above, late pregnancy is when nutritional requirements increase significantly, and residents require crucial adjustments to their diet. Although this is when they need to eat more, they may actually stop eating as much due to the lack of physical space as the foal grows (around a pound a day!).

At this point, concentrates are often added to their diet, if they haven’t been already, to help meet their energy requirements. However, It is vital that quality forage still makes up the majority of their diet, followed by small meals of concentrates. Some sources say this is up to 6-8 lbs for the average-sized mare. Others stated ¾ to 1 pound of concentrate per every 100 pounds of the mare was a good guideline. During this time, mares will generally need mineral supplementation. In order to maintain or increase body weight during late gestation, an average-sized mare will require 20-25lbs of quality forage and pasture in addition to the recommended concentrates. During this time, their protein requirements will be increased to around 10-20%, calcium to 0.45%, and phosphorus to 0.35%. According to The National Research Council’s Nutrient Requirements of Horses, a 12% crude protein ration should generally meet protein requirements. A grass/alfalfa mix forage may be recommended, which will also affect the amount of grain and supplementation needed. Vitamin A supplementation may be recommended as well. A ration balancer can also help them get all the nutrients they need. 

Don’t Overfeed
Although it sounds like a pregnant resident needs extreme amounts of food, it is important not to overfeed. Some studies show foals have a greater risk of developing metabolic bone disease if their mothers were overfed in the later stages of development. Mares that have been fed a diet high in sugars and starches were more likely to have foals that were resistant or sensitive to insulin. 

Early Lactation

Once a mare has her foal, the dietary requirements will increase significantly as her body works hard to nourish her little one. Some research states that mares make around 3 gallons of milk A DAY in the first five months after their foal is born. This is an average, of course; some mares may produce less, while others may produce up to 4 gallons! You can imagine how much energy that must take. To compensate for this, a lactating mare should consume between 2-3 percent of her body weight daily in hay and grain. Some may require fat supplementation to help them keep weight on and to provide nourishment for their foal. During this time, a mare’s protein requirements will be especially high.

Even though your resident may need more food after they give birth, it is still always important to adjust their diet gradually to reduce the chance of any issues, such as colic or laminitis. Multiple, smaller meals are always better than a large single meal. The amount of concentrates they need depends on their access to quality pasture and hay. Someone who produces a lot of milk may need up to 2% of their body weight in concentrates in addition to their daily hay intake. Access to green, quality pasture will reduce the amount of concentrates needed, while poor grazing opportunities often increase their need for concentrate supplementation. An average lactating mare (1,100 pounds) may require 22 or more pounds daily of decent hay. The same mare may also require 13-15 pounds of concentrates (more if the hay is of poorer quality). Mixed hay and alfalfa may be recommended during this time.

Late/End Of Lactation

As time passes, the mare will start producing less milk and won’t have such high dietary demands. This usually begins around months 4-5 and slowly decreases from there. At this point, you will start reducing the amount of hay, concentrates, and additional supplementation. 

Winter Considerations
If you live in an area that experiences cold seasons, there are extra factors to consider. There will be less or no quality forage in the pasture. Extreme cold weather can also increase the energy requirements of residents. A pregnant resident may already have increased energy requirements. This makes it especially important to ensure they get the necessary nutrients.

We hope this brief introduction to nutritional considerations for pregnant and lactating mare residents has helped you build a foundational understanding of their dietary needs. This foundation will help you converse with veterinarians and equine nutritionists when consulting them on pregnant or lactating mare resident diets.

SOURCES

Mare Nutrition |  University Of Wisconsin Madison  (Non-Compassionate Source)

Nutrition Of The Broodmare | University Of Kentucky, Department Of Agriculture  (Non-Compassionate Source)

Nutrition Management Of Pregnant And Lactating Mares | University Of Nebraska Lincoln – Extension  (Non-Compassionate Source)

Nutrition For The Pregnant And Lactating Broodmare | Badger Equine Veterinary Services  (Non-Compassionate Source)

Nutrition For The Gestating And Lactating Mare | Iowa State University Extension And OutreachAn activity or campaign to share information with the public or a specific group. Typically used in reference to an organization’s efforts to share their mission.  (Non-Compassionate Source)

Broodmare Nutrition: Lactation Remains Most Demanding Period | DVMDoctor of Veterinary Medicine, an academic degree awarded to veterinarians in many countries. (Non-Compassionate Source) 

Energy Requirements And The Feeding Of Mares During Lactation: A Review | Journal Of Equine Veterinary Science (Non-Compassionate Source) 

Feeding The Broodmare For The Health Of The Foal | DVM (Non-Compassionate Source) 

Nutrition Of Mares Influences Milk Characteristics And Development Of Foals | Equinews (Non-Compassionate Source) 

Non-Compassionate Source?
If a source includes the (Non-Compassionate Source) tag, it means that we do not endorse that particular source’s views about animals, even if some of their insights are valuable from a care perspective. See a more detailed explanation here.