11/09/01

                                                                                                          

 

 

Name of disorder

 

Early Embryonic Death (EED)

 

Species of animal affected

 

Although EED can happen in any species the paper will deal with it in the horse.


Effects on reproduction

 

In horses, EED is thought to be the cause of infertility in nearly twenty percent of the mares and higher than seventy percent in subfertile mares.  EED is considered loss of the embryo before the fortieth day of gestation.  Many mares show little or no signs of EED, there is little to no vaginal bleeding after EED.  Some noticeable signs of EED include failure to return to heat at the normal time and if the EED happens after the thirty-sixth day of gestation the endometrail cups are already functional and will secrete chorionic gonadotropin for 110 to 120 days even with out the presence of a fetus. This will keep the mare from showing signs of heat and may delay her breeding to the next season. 

 

Causative agent

 

EED can be caused by many factors including chronic endometritis, progesterone deficiency or chromosomal defects.  Chronic endometritis is an infection of the lining of the uterus caused commonly by bacteria such as streptococcus zooepidemicus, E. coli, Pseudomonas aeroginosa can cause EED through three different paths. The first path occurs before the seventeenth day of gestation, when the embryo is free moving and is nourished by secretions for the endometrail glands.  If these glands do not produce enough secretions to support the embryo during this phase the embryo will not survive.  The second pathway for chronic endometritis to cause EED involves release of prostaglandin from infected endometrium. This release of hormones causes the corpus luteum to lysis prematurely, causing progesterone levels, necessary for maintaining pregnancy, to drop and the termination of the pregnancy. The third pathway is caused of the bacteria and inflammation products as a result of the infection of the endometrium.  The products and effects of these bacteria can prove lethal for embryos during the early stages of pregnancy. 

Low levels or varying levels of progesterone during the pregnancy can also pose a treat to embryos. With out consistent and high levels of progesterone the mare’s body cannot sustain a pregnancy and her body may abort the conceptous in favor of returning to estrus. This variation in the levels of progesterone can because by chronic endometritis as well as other factors.  While chromosomal defects in horses are much less common in horses then in humans, many of these defects are incompatible with early embryonic development and cause death of the embryo.

 

Prevention and Control

           

Preventing EED by diagnosing choric endometritis before breeding, using an endometrail culture and biopsy, and treating the endometritis can reduce cases of EED and improve fertility in a number of mares. Treating endometritis can involve antibiotics to treat the bacterial infection and or flushing of the uterus to remove and clean the infection and inflammation.  Endometritis can also be prevented with proper hygienic practices and good conformation in mares. Reducing the number of services per mare and using artificial breeding technologies where possible help to reduce the change of infection with in the uterus.  Some conformational faults can be surgically corrected like pneumovagina, urovagina and incompetent cervix, all of which make a mare at higher risk for chronic endometritis. 

Ultra sounding infertile mares to follow the progress of embryonic development can help to find what is causing the EED by determining when the embryo is dying.  If the embryo is surviving past day eight but then dies in the following days embryo transfer can be used to produce a foal from a mare and avoid EED. Embryo transfer techniques are used to remove and embryo between day six and day eight post ovulation. By transferring the embryo to a healthy recipient mare the donor mare’s reproductive problems can be bypassed to produce a foal with her genetics.

Blood test to determine the concentration of blood progesterone is a good indicator of weather of not the mare is producing high and consistent progesterone levels.  Unstable levels of progesterone can be corrected by administering regumate, an oral progesterone to the mare for the first 180 days of pregnancy, this will reduce the variation in the hormone level and prevent EED.  After the 180-day treatment period the placenta takes over the function of maintaining hormone levels and the oral progesterone is no longer needed.

             

 

Work Cited

 

Darling, Kjersten D.V.M, and James M. Griffin, M.D. Veterinary Guide to Horse Breeding. New York: Howell Book House, 1999.

 

            Georgi, R. P., Et al. The Horse. 2nd ed. New York: W. H. Freeman and Company, 1990

           

Squires, E.L., P.M. McCue and D. Vanderwall. “The Current Status of Equine Embryo Transfer.” Theriogenology 51 (1999): 91-104.