INFERTILITY IN MARES! CAUSES
Story by VETERINARIAN, GENETICIST AND EQUINE NUTRICION WALTER RASPO
SANTA ROSA, LA PAMPA, ARGENTINA
ASESOR GENETICO (HARAS EL TALA)
(HARAS MDP) STUD EL REBERDE (VENADO TUERTO)
Infertility in the mare can be caused by a variety of factors or conditions without exception produce a similar result, a mare unable to produce a live foal. It seems hard to believe, but one of these conditions that causes infertility, occurs initially as a normal physiological response in 100% of the mares that are under a program of natural service or artificial insemination. Endometritis is the name given to the inflammation of the endometrium, a "layer" or mucous membrane lining the inside of the uterus, where the embryo is implanted for future development. The irony of this situation is that in principle it is produced with the intention of ensuring the survival of the future be, however, sometimes becomes the main obstacle to successfully complete the difficult task of producing a live, healthy foal.
Once the mare is "served" by a stallion or inseminated, sperm or male sex cells traveling through the uterus to reach tubular structures called oviducts. The oviducts connecting the uterus to the ovaries and they performed the union of sperm and egg, the female sex cell, then this is "liberated" from the ovary at ovulation.
The union of two sex cells of the oviduct at an embryo formed will start the development of a new being.
The embryo in the uterus passes back through the oviduct during the following 5-6 days after ovulation, after which, and in the womb, will be introduced later to complete their development until the formation of a new foal. So far seems to be no problem whatsoever, however, the entry of semen into the uterus along with bacteria and other pollutants not lost on local defense mechanisms of the uterus. Activation of physical mechanisms, cellular and immunological causes a local inflammatory response that aims only to "clean" the uterus. A failure in the removal of these contaminants factors quickly involve a uterine environment unsuitable for the moment that returns the embryo to the uterus and a serious obstacle to the survival of the same.
In short after the "service", the stallion deposited in the uterus of mares with semen, bacteria and other pollutants that are recognized by the local defense of the uterus as foreign. The uterus reacts against these external agents generating a temporary inflammatory response in a quick and effective way to "clean" the uterus of the mare within 96 hours after service. This will allow the environment to ensure proper uterine embryonic life and eliminate external agents generators inflammation.
We could then ask: If this behavior or is physiologically normal inflammatory response and occurs in every mare that is "served", where is the difference between the group of fertile mares that retain their pregnancy to the end and another that despite react in the same way before the "invasion", fails in his attempt to conceive and returns in "heat" a few days after the service?. In the normal mare cellular defense mechanisms, immunological and physical are activated immediately after the service and recognize the semen, bacteria and small particles as components not specific to the uterus. Specialized defense cells of the white series migrate into the uterine lumen and reach their maximum activity 8 hours after encompassing service and digesting microscopic particulate pollutants and bacteria.
In the normal mare this cellular activity is so efficient that for 12 hours of service these cells have managed to fully control the situation and withdraw. Similarly the larger items are drained out of the uterus through the activation of physical mechanisms including vigorous uterine contractions and activating mucociliary apparatus. Thus the normal mare is capable of removing 60% of the polluting components in the first two hours of service and completely clean the uterine environment within the first 12 hours, removing the stimulus that maintains the inflammatory condition in utero sufficient time to await the arrival of the embryo to the uterine environment that guarantees the life of it. By contrast, in the group of mares who fail in their attempt to defend the uterus, cleaning and control of the inflammatory response are not met within a suitable time period. The reduction in the efficiency of defense mechanisms allows the rapid multiplication of bacteria which adhere to the wall of the uterus and maintain a permanent inflammatory state that causes embryonic death.
This type of mare who repeatedly fails in his attempt to carry a pregnancy to term despite being "served" with stallions of known fertility in breeding which makes a proper breeding management, mares are known as "problems" or susceptible to endometritis. Age is one factor that makes the horse more susceptible to suffer from chronic endometritis and uterine infections, in other words the older mare is more at risk than young mare. While the above is true, rather than age, is even more important when considering who is most likely to suffer from this condition, the number of births has had the mare. A mare of 10 years with 6 pregnancies may perhaps be more susceptible to endometritis that a mare 15 years with only two pregnancies.
Whether in mares and in mares certain age who have had multiple births, anatomical barriers that prevent entry of pollutants and irritants to the uterus, as the tone and shape of the vulva and the tone and strength of uterine contraction affected. This allows the entry of outsiders into the uterus and affects normal drainage thereof. Due to the large losses that occur every year about this problem among breeders and owners of mares, much money has been invested in their study, there are now specific management protocols to increase by a significant percentage the possibility of leading a term pregnancy in mares susceptible to endometritis.