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.
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Should Frozen-Thawed Semen Be Diluted Prior to Insemination?
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.
Retained Placenta in the Mare
Retained placenta (also known as retained fetal membranes) is the most common post-partum complication in mares. Typically, expulsion of the placenta occurs shortly after birth and it is considered retained if it is not expelled within 3 hours post-partum. The prevalence of retained placenta varies from 2 to 10% of foalings and can be as high as 30 -54% of uneventful births in Friesian mares. Retention of the placenta in mares should not be overlooked. Appropriate diagnosis and treatment should be quickly applied to prevent secondary, life threatening, complications.
Splitting Doses of Frozen Semen
“I just purchased one very expensive dose of frozen semen from this incredible stallion. Is it OK to split the dose and breed two mares to try and get two foals?” or “The stallion owner only provides one dose per heat cycle and my vet would like to use a timed insemination protocol. Is it OK to split the dose and inseminate twice on the heat cycle?” At SBS we have heard these questions or some variation of them many times over the years. The answers are not simple ones. This blog article will follow up on two previous blogs that are also important in understanding the issue. See the recent blogs What Exactly is a Dose of Frozen Semen? and What is Progressive Motility?