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by Kim and Kari Baker

Broodmare Nutrition

Mirror KB Equine Article Series

Feeding the Pregnant Mare

Kim and Kari Baker

Besides your mare’s elite pedigree, her ability to produce a quality, healthy foal primarily depends on proper care and feed.  If her foal is to be competitive in today’s world of fierce competition, yet remain sound it’s very important that he is healthy. 

In other words, this means that her foal must be furnished a proper balance of, protein, energy, minerals and vitamins not only from the time he is born, but from the moment he is conceived.

Plotting a feeding Program

The most common mistakes horse owners make in feeding their broodmares are underfeeding minerals and vitamins during gestation, yet over feeding protein and energy during this same period. Owners further tend to error in underfeeding the protein and energy feeds during the key months of lactation. Keeping this in mind, how might the broodmare owner steer clear of making these, and other nutritional blunders?

When strategizing and managing a feeding program for your broodmare, you must be able to recognize quality feed stuff as well as make an effort to obtain a working knowledge of a good number of nutrients that are present in her feed.  This involves not only the commercial grains that you choose to feed her, but also that of supplements, hay, and even the pasture grass she grazes.

Age, size, daily physical activity, as well as her stage in pregnancy must be taken into consideration when developing a diet that will address the mare’s entire nutritional requirements, as well as those of her fetus.

Broodmares fall into one of two key groups, those that don’t have foals at their side, and those that do.  During early gestation, nutrient requirement in the second group, those with foals at their side, is much higher than in the first group.  This is solely due to the burden of lactation (the production of milk) in the nursing mare.

Fetal Nutrition

First let’s take a moment to look at and understand exactly how the fetus obtains it’s nourishment and how the mare’s diet during pregnancy will influence the growing foal.

Within 24 hours after conception, the fertilized egg begins to undergo important cellular divisions, continuing to divide for three to four days.  In the very beginning the conceptus must rely solely on nutrients that are present within its own cellular fluid

As all this is taking place the mass of cells embark on a journey through the oviduct, where it finally reaches the uterus on about the sixth day.  At this point germ cell layers form membranes around the embryo to create the yolk sac from which the embryo’s survival will depend on the production of uterine milk.

Blood vessels soon proliferate the yolk sac forming a system that will readily transport nutrients from the yolk sac to the embryo.  The yolk sac will continue to carry out this nutrient transport function up to the time placental membranes and the umbilical cord, begin to take over the job, which takes place somewhere between day 21 and day 35 post-conception.

Fetal nutrition seems to be most critical between day 25 and 31 of gestation.  However, it’s not fully understood exactly what causes the embryonic losses that occur at this time.  Losses might simply be the result of insufficient nutrients or imbalances, or may be contributed to a sensitivity of nutritional deficiencies while the change in relationship between the embryonic membranes and the endometrium take place.

In the latter part of gestation the fetus will counter any nutritional shortage by reducing it’s own rate of growth, and will likely result in a foal with a low birth weight that may lack energy to stand and nurse.

The influence of a nutritional deficiency or imbalance on the normal growth of the fetus will depend on the type of nutrient implicated and what stage of development the foal is in.  Most problems occur during early gestation when specialized body structures are being formed.

Broodmare Nutrition

Now let’s consider what nutrient demands are placed on the broodmare.  Like all horses, her nutritional requirements include water, minerals, vitamins, protein and energy.


Water, of course is the most important life-sustaining nutrient and must be available in plentiful quantities at all times. Keep in mind that the intake of water will increase in the lactating mare.

Protein and Energy

The broodmare in early gestation will do quite well on diets consisting of 10 to 12 percent protein.

“For the first seven to eight months of pregnancy, as long as she is in good flesh with a body index of five to six, the mare’s nutritional requirement is basically what a non-pregnant mare needs,” says equine nutritionist, Eve Finkelstein of Poland, Maine.  If a good grass pasture is unavailable, the broodmare should be offered enough quality grass or grass/legume mix hay that will keep her body condition in moderate flesh.

“At this time the fetus is laying down critical organs but is not making increased energy demands on the mare,” says Finkelstein.  Thus, due to the minimal growth of the fetus during the early stages of pregnancy, the broodmare will generally require no more protein or digestible energy than that of the average idle mature horse.

However, if the mare is to be used under saddle or in harness during pregnancy, her energy needs will escalate just as any other performance horse’s energy needs increase due to expended energy.

As the broodmare enters the last trimester of pregnancy, her need for protein, as well as digestible energy increases.  This is due to the increased rate of growth of the unborn foal, with a dramatic weight gain of about one pound per day.

“Just prior to foaling, the mare should be consuming 2.5 to 3 percent of her total body weight in feed per day,” says Finkelstein.  “Because the foal is rapidly growing and is pressing on the mare’s internal organs, she will likely require smaller meals several times a day.”

Although some people feel the need to feed protein at 16 percent, the broodmare in late gestation generally requires a total of only 12 to 14 percent.  “Too much protein results in excessive nitrogenous waste, which the mare will need to get rid of by drinking a lot of water and urinating excessively.”

Energy needs begin to increase by the seventh month and will continue to increase through the remainder of gestation and early lactation.

Keep in mind too, that most regions of the country are well in the throes of winter while the broodmare is in her last trimester of pregnancy.  As the temperature drops, the mare will need to expend more energy just to keep warm.  In fact her energy needs will increase one percent for each drop in degree below 60 degrees.

Vital nutrient requirements in the lactating broodmare may be as much as 75 percent over that which is required of the non-lactating mare during early gestation.  In the first three months following parturition, nutrient requirements for the production of milk is extremely high.  This is due to the fact that the transformation of the mare’s digested nutrients into milk is somewhat unproductive.  Indeed, it is only about 60 percent efficient.

Obviously this means that it will take a sizeable increase in energy for the mare to produce an adequate supply of milk for her growing foal.  And this might easily range anywhere from double to 75 percent over her own maintenance energy needs.

This should be supplied mainly as high quality forage with enough added feed supplement to eliminate any energy deficiency.  However, rapidly digested carbohydrates found in most concentrated grain feeds are associated with tying up, colic, and founder.  Therefore a balanced feed containing ten percent fat can be used to reduce high starch consumption from grain-based concentrates.

Vitamins and Minerals

Both the mare and the growing fetus throughout pregnancy require essential vitamins and minerals.

In early gestation, vitamins are extremely important nutrients, for at this time the cells that are developing and rapidly growing are in the process of establishing the specialized body parts of the foal.

Vitamins are separated into two major groups. Those that are fat soluble and those that are water-soluble. Specifically, the vitamins that are fat-soluble (A, D, E and K) are absorbed in membranes and nerve tissues that contain large amounts of fatty matter, while water-soluble vitamins (the B group and C) are absorbed via the non-fat aqueous systems of the body.

When considering the growing fetus, A, D, E, and K, as well as the B group of vitamins are the primary micronutrients one should look at.

Vitamin A, which is stored in the liver, is central in forming healthy epithelium, the cells that are responsible in generating tissues such as the skin.  It’s also necessary for proper bone development and the utilization of protein, as well as providing the horse with the ability to resist infections.

The B vitamins (riboflavin, thiamine, niacin, pantothenic acid and B12) are vital for red blood cell formation as well as normal organ development in the foal whereas vitamin K is a necessary product that equips the blood with the means to clot.

Calcium, while not a vitamin but an important mineral that is necessary in the formation of the skeletal system, requires support from Vitamin D, which is abundant from daily exposure to sunshine.  Though indirectly significant to the fetus, vitamin E is essential for the developmental health of the mare’s ova and will later aid in lactation.  It is also thought that congenital defects may be linked to vitamin E deficiencies through the deprived ova’s ability to migrate and divide.

With all this being said, while vitamins are all very important, they are generally not required in supplementary amounts for the nonlactating pregnant mare since they are usually abundant through quality roughage.  If for some reason neither fresh pasture nor green quality hay is available to your mare, you may want to provide her with a vitamin supplement that will furnish her with these important nutrients.

However, be aware that providing the above essential vitamins, particularly those that are fat soluble, in excess can be just as detrimental as not furnishing them in adequate amounts.  For example, adding an over abundance of vitamin A and D to the mare’s diet during early gestation might cause severe limb abnormalities in the foal.

Now lets take a look at minerals.  These are divided into two classes, the macro minerals and the micro (trace) minerals.  Macro minerals, as a rule, are needed in larger amounts than trace minerals, and include calcium, magnesium, sodium, potassium and phosphorus. Necessary trace minerals include copper, cobalt, iron, iodine, manganese, selenium, and zinc.

"The interrelationship of minerals, both macro and trace are amazing, but extremely complex at the cellular level,” says Finkelstein. “It’s best to concentrate on the macro minerals first, having forage and grain supplements tested, then concentrate on the trace minerals since adding a mineral supplement could possibly cause some of the minerals to interact improperly or have you feeding a large amount of minerals with adverse effects on the growing embryo.”

Throughout pregnancy and lactation the broodmare will generally do quite well when provided a trace mineral salt block.  Be sure that selenium is included in the mineral block if the mare is grazing on or eating hay that is grown in selenium deficient areas. 

There are also selenium supplements that can be added to her feed, but this should be done cautiously to avoid selenium toxicity.

During the third trimester the fetus begins to take in and store the greatest amount of vitamins and minerals.

“Copper is required by the mare and fetus for the production of normal connective tissue; which includes tendons, ligaments, and the unborn foal’s framework of bones as well as the cartilage that lines the joints.  Deficiencies in copper may precipitate the onset of developmental bone disease such as (OCD) Osteochondrosis Dessicans,” explains Finkelstein.

On top of this, the mare’s requirement for calcium and phosphorus will double.  At this stage grass and grass hays may be deficient in these two minerals.  Alfalfa on the other hand is high in calcium, and adequate to deficient in phosphorus.  Therefore the lactating broodmare should do well on a good mix of grass and alfalfa hays.

Feeding the Broodmare

As in all horses, feed consumption should be based on the broodmare’s ideal weight with feed intake for the lactating mare generally ranging from two to three percent of the her body weight.  For instance, let’s choose to feed our 1,000-pound (455 kg) mare two and a half percent of her body weight.  This figures out to 25 pounds (11.4 kg) of total feed (roughage and grain) per day, and may further work out as 20 pounds (9.1 kg) of quality hay or forage and five pounds (2.3 kg) of a balanced feed concentrate.

If pasture grazing is unavailable, good quality hay must be supplied to the mare.  However, the rate at which the hay should be fed will, by in large, depend on the kind and quality of hay you choose to feed.

Quality free choice grass hay is ideal, but if this option does not fit into your feeding program, a good place to start would be to feed out about one percent of the mare’s body weight per day.  This means a 1000-pound mare should require nothing less than ten pounds of hay each day.

When considering roughage, the broodmare owner must bear in mind that all forages are not ideal for the broodmare.

While fescue grass is a good source of forage for the general population of horses, it is a poor choice for the broodmare if it is infected with an endophyte fungus.  Ingesting such fescue, either in the form of grass or hay, can result in early foal death, a thickened placenta and a deficient or total lack of milk production in the mare.

Furthermore, Sorghum and Sudan grasses have been known to cause incoordination in the hind end as well as severe bladder infections in both genders of horses.  Like the endophyte-laden fescue grass, grazing on these pastures may bring about agalactia (the absence of milk) in the broodmare.  Mares might also abort their fetuses or turn out weak newborns.

Not only are certain types of grasses unfit for the broodmare, but weeds growing along side pasture grasses or baled within hay can be harmful if not dangerous for both mare and foal.

For this reason it’s wise to carefully check pastures and identify both grass and weeds before putting the broodmare out to graze.  Do the same with any hay that will be given to the mare.  Local agricultural agents can help with the identification of plants.

Although most other forages are generally not harmful to the mare or the growing fetus, they are not likely to be created equal.  Minerals and vitamins in either grass or hay will vary depending on the, the mineral content of the soil in which it is grown, the species of the plant, its maturity, what stage of growth the plant is in when it is grazed or harvested, as well as the weather conditions present at the time.

For this reason it would be wise to obtain an analysis of both hay and pasture in order to balance your mare’s diet appropriately to her specific needs.

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