Once young colts and fillies reach the age of puberty their behavior may become an issue in the show ring or on the race track. Castrating a colt which you intend to use for breeding purposes may not be an option and mares are not typically permanently sterilized. Their sexual behavior may also cause problems with housing, trail riding, etc. In this article, Dr. Ed Squires discusses some of the common ways stallion and mare owners suppress the behavior of their horses.
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What Can Cause a Mare to Lose Her Pregnancy?
Mares can develop problems during pregnancy or be at high risk of losing the pregnancy for a variety of reasons. These include age (old mares frequently have endometriosis in which the uterus is unable to properly supply the fetus with appropriate blood supply and nutrients), physical conditions (placental and fetal fluid abnormalities; body wall tears; chronic debilitating conditions such as laminitis and Cushing’s disease), and acute disease or injury (placentitis, uterine torsion, surgical colic, colitis, acute laminitis, or fractures). When a mare becomes stressed or debilitated, inflammatory chemicals and prostaglandins increase and induce abnormal uterine contractions and potential pregnancy loss. Reproductive problems that arise during gestation, however, when detected and diagnosed early, can still result in the survival of the mare and usually the foal. The abnormalities most commonly seen during the middle to late stages of pregnancy will be discussed in this article.
Should Frozen-Thawed Semen Be Diluted Prior to Insemination?
For veterinarians and technicians accustomed to inseminating fresh or cooled semen in large (20-60 ml) volumes, the idea of inseminating 0.5 to 4 ml of thawed frozen semen can be intimidating. During processing, frozen semen is concentrated by centrifugation and is typically packaged in small 0.5 ml straws at a sperm concentration that is often as much as 5 to 10 times greater than cooled semen. Therefore, a full insemination dose of frozen semen may be contained in just a few milliliters of volume whereas the same number of sperm extended for cooling may require 30-40 ml of volume.
Influence of Mare Status When Breeding with Frozen Semen
Whether a mare is maiden, recently foaled, or barren can influence her ability to conceive when breeding her with frozen semen. The first pregnancy obtained by using frozen-thawed semen in the equine species dates back to 1957 and was obtained using epididymal semen. However, for many years this reproductive technology has achieved limited progress in the horse compared with other species such as cattle. This was mainly because for a very long period of time only a few horse registries allowed the use of frozen-thawed semen. Hence, economic interests and resources allocated to research have always been minimal and as a result obstructing advances in this area.
How to Prepare the Older Mare for Breeding Season
Older mares have a knack for being the sweetest and gentlest mares on the farm. We see them year after year, either carrying their own foals or returning to donate embryos if their reproductive status requires. Oftentimes, these mares are considered “special” patients, requiring a unique combination of diet, exercise, and metabolic support to maintain their physical and reproductive health. We often see older performance mares that are being bred for the first time following a long and successful show career. Reproductive problems such as cervical adhesions and uterine infection can be common in older mares which affect their ability to carry a foal or donate an embryo.
Biofilms in Mare Reproduction
A biofilm has been proposed to have a significant role in chronic infections in the horse. It has been suggested for over a decade that chronic uterine infections resistant to antimicrobials may be due to biofilm production. The involvement of a biofilm in cases of bacterial endometritis has not been clearly elucidated, but many reproductive specialists suspect a biofilm plays a significant role in infectious endometritis. In this article Dr. Ryan Ferris, a board certified theriogenologist from Colorado State University, explains the lifestyles of bacteria, how a biofilm is formed, how they protect bacteria and their implications on equine reproduction.
Cryopreservation of Equine Embryos
Embryo vitrification doesn't sound much like "freezing embryos,” but the end product certainly is a cryopreserved equine embryo, frozen in liquid nitrogen for the preservation of genetics and transfer into a recipient mare at a later time. For the sake of some readers of this blog, an embryo is the result of fertilizing an oocyte (egg) with sperm and allowing the initial stages of development to occur. Embryo vitrification is the process whereby we freeze equine embryos for storage for indefinite periods of time prior to transfer into a recipient mare. We have the technology to cryopreserve equine sperm and equine embryos, but not equine oocytes. Herein lays the answer to the most common question that comes up in conversation regarding this blog topic. Some readers assume that since we can freeze the male generated sperm, we can likewise freeze the female generated oocyte. Unfortunately, due to some very sensitive cytoskeletal components in the oocyte, the technology does not exist to freeze equine oocytes. As we proceed, you will understand the process of embryo vitrification and we will delve into areas of research that are improving the success rates of vitrified embryos in generating live foals.
Why Freeze Equine Embryos?
Ovum Pickup in the Mare
Breeding horses has come a long ways in the last 50 years. Veterinarians have been able to overcome many of the obstacles presented when breeding horses with advancements in artificial insemination and embryo transfer. However, there are still times when infertility of either the mare, stallion or both prevent getting foals on the ground. The most recent advances in assisted reproductive technologies, Ovum Pickup and Intra-Cytoplasmic Sperm Injection (ICSI), have allowed us at Weatherford Equine Breeding Center (WEBC) to take the next step in overcoming these obstacles with some promising results.
Effect of Number and Timing of Equine Frozen Semen Inseminations on Fertility
Further expansion in the use of frozen semen is dependent upon developing simplified strategies for insemination. SBS has developed a timed insemination protocol where mares are only examined once per day during estrus and inseminated at 24 and 40 hr after hCG or 30 and 40 hr after GnRH. This approach allows frozen semen mares to be managed similar to those bred with cooled shipped semen. A couple of arguments against this approach with frozen semen is that it takes too much semen when mares are bred twice in one cycle and that if the mare is inseminated more than once per cycle the fertility will be lowered because of post-breeding induced endometritis.
Heat Stress and Equine Reproduction
During those dog days of late summer and the end of the breeding season, most of us who work in equine reproduction are ready for a break. You are left with those difficult mares that didn’t settle earlier in the season and stallions that may be growing tired of breeding. Mares may not cycle as predictably or conceive as readily and stallions may be tougher to collect or exhibit a decrease in semen quality. One of the factors that can contribute to these problems is heat stress. As ambient temperatures rise, stallions and mares may experience disruptions to normal reproductive function as a result. This article will briefly describe some of the effects of heat stress on mare and stallion reproductive function.