*scroll to bottom to view a foaling and a castration video
Reproductively the mare is termed seasonally polyestrous, meaning that during the breeding season (March/April through to Sept./Oct.) she will go through multiple estrous cycles. These cycles are 21 days in length and their onset is triggered by increasing daylight. Each of these 21 day cycles can be divided into 4 segments: Proestrus lasts about 4 days and during this period the ovarian follicles which contain the eggs are growing in size and number. Estrus follows and this is the time the mare appears to be "in heat". One follicle has become dominant and grows larger than any other follicle. Estrogen levels are now at their highest. During this time the mare becomes receptive to the sexual advances of the stallion. Breeding (either natural or AI} would be done during this period. The estrus period lasts about 5-7 days and ovulation or release of the egg occurs 24-48 hours before its end. After estrus comes metestrus which also lasts about 4 days. During metestrus the cells lining the ovulated follicle are changing. While in estrus they were producing estrogen but now switch to progesterone. The last stage of the estrous cycle is diestrus which is the longest stage. During diestrus an ovarian structure called the CL (corpus luteum) produces high levels of progesterone and thereby prevents the initiation of another cycle. As long as the CL persists the mare will not go into heat again. At the end of diestrus a hormone called prostaglandin is released from the uterus and causes the CL to regress. This regression reduces circulating progesterone and allows another cycle to begin.
As stated above the mare is bred while in the estrus phase of the cycle (either natural cover or artificial insemmination). Fertilization will occur in the oviduct and the fertilized embryo will remain there for about 5 days. After this the embryo is transported into the uterus itself. For about 16 days the embryo will migrate throughout the horns and body of the uterus. After day 16 the embryo will implant itself in one of the horns and will remain there throughout the pregnancy. Confirmation of pregnancy is usually done with the ultrasound at about day 16 (see pics below). Twin pregnacies would be diagnosed at this time as well. If fertilization did not occur then the egg will be resorbed from the oviduct and a new 21 day cycle will begin. Pregnancy status should be re-checked rectally after day 40.
14 day embryo
23 day embryo
35 day embryo
The average length of gestation in the horse is about 340 days, although normal pregnancies may be as short as 320 days or as long as 365 days. During gestation the mare should recieve rhinopneumonitis vaccinations at 3,5,7 and 9 months.She should recieve all yearly vaccines at the 9-10th month. Routine deworming should be carried out as scheduled up until the last month. Nutritional requirements will increase up to about 30% in the last trimester of pregnancy. Normal exercise is appropriate for the pregnant mare.
Parturition itself is often divided into three stages. During stage one, which lasts about 4 hours there is uterine muscular contraction which causes abdominal discomfort. The mare may get up and down, paw, pass small amounts of urine and manure, look back at the flanks and sweat. The next phase is when the fetus moves into the birth canal, the "water breaks", there are abdominal contractions, and the foal is delivered. Delivery of the fetus normally occurs within about 20-30 minutes from the time of the water breaking. The third stage is when the placental membranes are passed and the uterus begins to shrink down (uterine involution) to normal size. The placenta should be passed within about 4-6 hours. If the placental membranes remain after 4 hours the veterinarian should be contacted. Retained placental membranes (as seen in the picture below) in the mare is considered an emergency as the toxins released by these retained membranes can be life threatening to the horse.
Membranes from a retained placenta.
Once delivered, the mare and foal should be left alone and the foal will usually get up within an hour or so, breaking the umbilical cord (clients should never break the umbilical cord prematurely). The two most important steps in preventing neonatal infections are disinfecting the naval stump (this should be done with betadine at least 2-3 times in the first day of life) and insuring adequate ingestion of colostrum. The colostrum contains all the antibody protection that the foal will get as there is no intrauterine antibody transfer in the horse. The foal will usually be up and nursing within a couple of hours. Giving the foal an enema at this time is a good idea as long as it is done gently and with appropriate restraint. In our practice we recommend a post foaling visit 18-24 hours after birth (assuming no problems). At this time the mare and foal are examined, blood is taken from the foal to measure antibody levels and the placenta is examined to make sure it has been passed intact.
PRE-BREEDING EXAMINATION:
Prior to breeding a mare it is recommended a pre-breeding examination be performed. The following procedures are recommended to insure the greatest chance for a successful breeding outcome:
1. Visual examination of the external genitalia (the picture below is a good example of why this procedure is done)
Vulvar growth. (this tumor was eventually removed with the emasculator).
2. rectal examination (allows palpation of the reproductive organs)
3. ultrasound examination (allows visualization of the reproductive organs)
4. vaginal speculum examination (allows for cervical evaluation and determine presence of intact hymen)
5. uterine culture (make sure there is no infection in the uterus)
6 uterine biopsy (done only in mares with a history of reproductive problems)
University of PA Veterinary School website: lots of info and a nice repro section below:
This link has both pictures and videos -------------------->
Reproductively the mare is termed seasonally polyestrous, meaning that during the breeding season (March/April through to Sept./Oct.) she will go through multiple estrous cycles. These cycles are 21 days in length and their onset is triggered by increasing daylight. Each of these 21 day cycles can be divided into 4 segments: Proestrus lasts about 4 days and during this period the ovarian follicles which contain the eggs are growing in size and number. Estrus follows and this is the time the mare appears to be "in heat". One follicle has become dominant and grows larger than any other follicle. Estrogen levels are now at their highest. During this time the mare becomes receptive to the sexual advances of the stallion. Breeding (either natural or AI} would be done during this period. The estrus period lasts about 5-7 days and ovulation or release of the egg occurs 24-48 hours before its end. After estrus comes metestrus which also lasts about 4 days. During metestrus the cells lining the ovulated follicle are changing. While in estrus they were producing estrogen but now switch to progesterone. The last stage of the estrous cycle is diestrus which is the longest stage. During diestrus an ovarian structure called the CL (corpus luteum) produces high levels of progesterone and thereby prevents the initiation of another cycle. As long as the CL persists the mare will not go into heat again. At the end of diestrus a hormone called prostaglandin is released from the uterus and causes the CL to regress. This regression reduces circulating progesterone and allows another cycle to begin.
14 day embryo
23 day embryo
35 day embryo
Membranes from a retained placenta.
Vulvar growth. (this tumor was eventually removed with the emasculator).