by Dr. Frederick Harper
Extension Horse Specialist
Animal Science Department
University of Tennessee
 
Do you take vitamins? As a society, we are very conscientious about vitamins.
 
The same is true about many horse owners who provide supplemental vitamins to their horses.
 
Often with a balanced ration, such vitamin supplementation may not be necessary, especially in pleasure horses.
 
But recent research has shown that supplemental vitamin E may be beneficial when fed to mares in late pregnancy.
 
Why would this research be important to broodmare owners?
 
Foals are born without any natural immunity to diseases, and it is several weeks before their immune system is functional. To survive, foals must acquire passive immunity from their dam’s colostrum or first milk. For about a month before foaling, mares concentrate immunoglobulins in their colostrum.
 
Immunoglobulins contain antibodies which protects the foal from early diseases. The major immunoglobulin is IgG, but IgA and IgM are also important. Colostrum also provides the foal with other special nutritional needs.
 
Immunoglobulins are rather large molecules that normally are too big to be absorbed by the foal’s intestinal tract. But nature makes it possible for the foal’s intestinal tract to absorb immunoglobulins for a few hours after birth.
 
Foals may become sick and die without adequate immunoglobulins. Several factors are critical in this process: 1) adequate immunoglobulin levels in the colostrum; 2) early and frequent nursing to obtain immunoglobulins and 3) the intestinal tract’s ability to absorb these large immunoglobulins. Failure of passive transfer occurs if this process does not work properly.
 
Researchers at the University of Connecticut divided 12 pregnant mares into two groups based on breed, age and expected foal date.
 
The mixed grass hay/grain diet fed met the National Research Council’s vitamin and mineral recommendations. Half the mares were supplemented to get the required level of 36 International Units (IU) of vitamin E per pound of feed daily while the other mares got 73 IU of vitamin E or twice as much daily.
 
The good news from this research is the serum and colostrum IgG levels were greater in those mares that received the higher level of added vitamin E.
 
All foal’s serum IgG, IgA, and IgM levels were similar at birth. After nursing, foals from the higher vitamin E supplemented mares had larger serum IgG and IgA values reflective of their dam’s colostrum.
 
From these data, it appears that supplementing mares with higher levels of vitamin E the last months of pregnancy improves both their serum and colostral immunoglobulin levels as well as their nursing foal’s blood level; thus, reducing possible failure of passive transfer.
 
Broodmare owners can enhance this process by supplementing mares so they get about twice the vitamin E required in the last months of pregnancy which would be about 73 IU per pound of feed. Green pasture forages, wheat germ oil, corn and soybean oils are good vitamin E sources. Hays however lose vitamin E content in harvesting, curing, and storage. If one feeds a commercial vitamin E supplement, use one with a high vitamin E content.
 
Mares foaling before spring pasture is available should be supplemented with vitamin E. It seems advisable to continue supplementation for at least a month after foaling or until the mares are on good-quality spring pasture.
 
Mares known to have poor quality colostrum or foals that have had failure of passive transfer also should be supplemented with vitamin E at twice the required level.