The Mare, the Foal-to-be and the Foal

Beneficial Bacteria and Yeast for the Pregnant and Lactating Mare

Larry Roth, Ph.D.

Proper care of the mare during gestation and lactation determines the health of the mare, current foal and the foal-to-be.

 Improving diet utilization can aid the mare in meeting heavy nutrient demands, hormonal changes and immune system challenges during gestation and lactation.

A review of recent research suggests that beneficial bacteria, live yeast and yeast culture will be useful for mares during the gestation and lactation periods.


100 days and Counting

Nutrition for the pregnant mare is actually the feeding of two animals: the mare and developing foal.  Over 50% of the fetus’ growth occurs during the final 100 days of the mare’s 340-day gestation period.

Inadequate nutrient intake by the mare during the final third of gestation can restrict fetal development and may result in the birth of a weak foal.  The mare must be in proper body condition at foaling to withstand the rigors of giving birth, initiating lactation and, if desired, being prepared to conceive at the foal heat. A mare encountering an energy deficiency will ration its energy supplies on a priority basis to body maintenance first, lactation second and lastly to producing a future foal.



Colostrum, the first milk produced after foaling, is richer in proteins, minerals and vitamins than later milk.

The high protein content results from elevated levels of globulin and albumin.

These immune bodies are transferred from the mare’s blood to the milk and ingested by the new-born foal for disease resistance. The mare’s health status during the later stages of gestation will determine the amount and quality of colostrum produced for the new-born foal.

While the importance of the foal consuming colostrum is well recognized, the impact of nutrition on colostrum quality and quantity is less acknowledged.

The new-born foal is dependent upon the mare’s milk for nutrients for growth and support of the immune system. Although the lactating mare and cow are different animals, basic nutritional and physiological factors are applicable to both sets of mothers.

Milk quality and quantity are definitely impacted by the balance and quantity of nutrients consumed.

Proper supplementation of minerals and vitamins is the foundation for a good lactating mare program. A calcium deficient diet for the mare can result in poor skeletal growth by the nursing foal.

 The mare’s intake of energy and protein will determine the energy and protein

content of the milk available to the foal.

Diseases contracted by the foal may determine its health and performance as an adult. The

milk will be the sole source of building blocks for the foal’s immune system. Hence the

importance of proper nutrition to the mare to ensure a fast start to the foal’s young life.


Maximizing Diet Utilization

After working with your veterinarian and nutritionist to select proper gestation and lactation

rations for your mares, it is time to maximize diet utilization. The small intestine is the

principle site of absorption for amino acids, vitamins, minerals and fats. Energy absorption

will occur in both the small and large intestines. Starch that is not digested and absorbed in

the small intestine will be fermented in the large intestine. Fiber from grazed and harvested

forages is fermented only in the large intestine. Some products of large intestinal

fermentation are absorbed and utilized as energy sources. However, excessive starch

fermentation results in digestive disorders, including colic.


Direct-fed Microbials or Probiotics

Scientists and horse owners are becoming acquainted with the opportunities to use direct-fed

microbial products, or probiotics, during the gestation and lactation periods of horses. Horse

owners have actually been enjoying the benefits of helpful bacteria and yeast for centuries.

Direct-fed microbials are species of beneficial bacteria and yeast reviewed by the Center for

Veterinary Medicine of the Food and Drug Administration and found to present no safety

concerns when used as direct-fed microbial products. It is important to note that these

products are not drugs and should not be viewed as such. Beneficial bacteria, including

Lactobacillus acidophilus and Enterococcus faecium, are preserved by freeze-drying and fed

as live, viable microorganisms. Yeast products available to the horse owner include active dry

yeast and yeast culture. Active dry yeast products feature live yeast cells dried to maintain a

large portion of their fermenting capability. Yeast culture products are composed of the yeast

cells and the yeast’s growth media; and the products are dried to preserve some of the

yeast’s fermentation capabilities (Assoc. of American Feed control Officials).


Beneficial Bacteria

Research documents the ability of the beneficial bacteria Lactobacillus acidophilus and

Enterococcus faecium to attach to the lining of the small intestine to enhance nutrient

absorption. Nutrient absorption is a major energy expenditure by the animal. Studies

indicate that the binding of beneficial bacteria to the intestinal lining reduces the energy costs

associated with nutrient absorption. Consequently, more energy would be available to the

animal. Therefore, supplementing beneficial bacteria to the gestating or lactating mare could

potentially increase nutrient absorption while lowering the energy expended. Attachment to

the small intestine lining also reduces the opportunities for harmful bacteria, such as E. coli or

Salmonella to adhere and increase in number.


Yeast and Yeast Culture

Several studies, notably by Glades and coworkers, have demonstrated improved milk quality

and quantity by mares supplemented with yeast products, and consequently improved foal

growth. The yeast products supply enzymes, B-vitamins and other factors to stimulate

beneficial bacteria in the small and large intestine. Enhancing fiber fermentation increases

energy availability to the mare for gestation or lactation needs. In addition, increasing the

amount of energy derived from forages could allow a reduction in the amount of grain fed.

Lowering the grain content of the ration could potentially reduce the risks of digestive upsets.

However, any decisions concerning the level of grain feeding should be based on body

condition and anticipated animal requirements.


Easy to Use

Direct-fed microbial products are available as dry powders to be simply mixed in the feed or

top-dressed on a once daily basis. An off-feed horse can receive the direct-fed microbials via

gel or paste products placed directly in the horse’s mouth. The direct-fed microbial products

should be stored at room temperature or refrigerated if possible to maintain viability. The

beneficial microorganisms are alive and become more active with elevated temperatures.

However, the "warmed-up and active" desirable bacteria and yeast eventually deplete their

energy reserves and die. Proper storage and handling of the direct-fed microbial products

will allow your horses to fully realize the potential benefits.

Horse owners have been providing beneficial bacteria and yeast to their animals and

enjoying the results unknowingly for many centuries. Understanding the nutritional needs of

gestating and lactating mares highlights many opportunities for direct-fed microbial product

usage. Research studies indicate that direct-fed microbial products can aid gestating and

lactating in maximizing diet utilization for producing healthy and active foals.


Larry Roth, Ph.D. is a Research Scientist with Conklin Co. Inc. 551 Valley Park Drive, Shakopee, MN 55379.

Dr. Roth conducts research on the benefits of direct-fed microbial products with food-producing and companion animals, as well as writes and speaks in the U.S. and internationally on the topic. Questions can be forwarded to Dr. Roth at Conklin Co. Inc.