Equine Breeding for Maximum Fertility

  • Since man has decided that Jan 1st  is the universal birthday for all horses in the Northern Hemisphere, man's breeding season for the horse is different than the mare's breeding season.
  • Horse owners desire foals to be born as close to Jan 1st as possible so they are bigger within their age group when young. (Even though it has been shown that there is no increased economic benefit in the lifetime of the horse.)
  • This creates breeding problems by forcing breeding into the non physiologic breeding season, but keeps theriogenologists employed!
  • Records of foaling, palpation, teasing, breeding are essential in maximizing efficiency.
  • Use the records to calculate reproductive parameters such as breedings/conception, heat cycles/conception, dates of conception, and foal heat conception.
  • Keeping good records allows identification of problems before a catastrophe strikes without you being aware of it.
  • The three most important words in horse breeding are Tease! Tease! Tease!
  • You must detect heat to breed efficiently and teasing is essential to detect heat.

Following a mare's cycles with teasing.
  • Even though there is no homosexual behavior (riding) like cows in horses, estrus detection in horses in easier than cows because of the longer duration of estrus.

Teasing Systems
  • You must use a stallion to tease efficiently. A 'proud cut' gelding is not an efficient teaser. Shetland studs work well because they are small and very ......shall we say, sexually aggressive.
  • The stallion will give a typical flehman response when exposed to an estrual mare.
Individual teasing
  • This is done one mare at a time and is very time consuming, but is the best way to accurately detect estrus.
  • Tease head to head, then the stallion's head to the mare's tail.
  • A teasing rail and a race or alley can be designed to tease many mares in a short time.
Modified individual teasing
  • A group of mares is allowed contact with a stallion, so many mares/stallion are exposed.

Mare coming to a stall window where stallion is housed.
  • The mares may confined and the stallion free to roam and find the mares in heat or the stallion may be confined and the mares seek the stallion.
  • Shy mares may not show estrus very well in this type of teasing system.

Another way to tease!

How often should you tease ?
  • Daily teasing is best, but is really not needed. Tease at least every other day. We normally tease on Mondays, Wednesdays, and Fridays and have good heat detection.
  • It is important to tease all the mares that may come into heat, not just the ones you think should be coming into heat.
  • Tease all the mares into heat, through heat and safely out of heat and into pregnancy until pregnancy is safely confirmed.

Breeding techniques
  • Natural service is required by some breed associations (such as the Jockey Club)
  • Breeding should be done ideally at ovulation, but this requires frequent palpation during estrus.
  • If the stallion power is available breeding every other day until the mare is out of heat will work well.
  • If you breed early in the year however, you may exhaust the stallion with no pregnancies breeding transitional mares.
  • A common practice is to start breeding on the second day of heat and breed every other day.
  • Since this does require more stallion power, you will need to depend on a breeding soundness examination of the stallion and record analysis to keep the breeding running efficiently.
  • Many popular Thoroughbred stallions breed twice a day (sometimes three times a day) during the peak season with good results.
  • Libido sometimes becomes a concern
  • This is a case where you may need to 'desynchronize' the mares so you do not have as many mares in heat all at once.
  • If there are too many mares for the stallion to breed, you may need to palpate and breed only at ovulation, but this takes skill by the veterinarian.
  • Natural breeding is more dangerous to all involved, including the stallion, mare and handlers.
  • Natural breeding also allows contamination of the mare and stallion and spread of venereal disease.
Artificial Insemination (AI)

Collecting semen for artificial insemination.

Advantages of AI
  • With AI there is less chance of venereal disease spread,
  • You can spread out the stallion to more mares.
  • You can collect semen using a dummy mount, which won't kick the stallion.
  • You can evaluate the semen for each breeding.
  • You can use a Minimum Contamination Technique (MCT), which decreases the introduction of contaminants into the mare. With this technique you put antibiotics in the semen extender, or if breeding Thoroughbreds, you place extender into the uterus of the mare that is being bred naturally.
  • Tease the mares into heat.
  • Palpate and/or ultrasound for a 35 mm follicle.
  • Collect semen from the stallion and inseminate a minimum of 500 million normal, motile cells into the uterus. The volume of the insemination is not important ( at least if it less than about 100 ml), only that there are enough motile sperm cells.
  • You can use fresh or extended semen.
  • Up to 20 inseminations/ejaculate are possible from some stallions.
Chilled semen
  • Many breeds (of course not the Thoroughbreds) allow the use of chilled, extended, transported semen.
  • To inseminate mares using chilled semen they are usually palpated daily and the day of ovulation is predicted by the softness of the follicle and the ultrasonic appearance. When you feel the follicle is about 2 days before ovulation, you order semen. They usually will collect the same day and ship it to arrive the next......hopefully. This means semen will come the day before she ovulates and everything will be perfect! Not so!!!! Many times the stallion collection schedule does not work out, for example, you need the semen tomorrow and they have already collected him today and shipped all the semen out. The next collection will not be until the day after tomorrow. Now you have a mare ready to ovulate and no semen coming.
  • An easier way is to palpate/ultrasound until a 30-35 mm follicle is present, order the semen and give hCG after the semen is in the mare. We usually wait until the semen is in the mare before giving hCG, because there are many instances you give hCG before getting the semen and then something delays the semen. Now what? The mare is going to ovulate and you have not semen.
  • Inseminate 500 million normal motile cells
  • Expect 10% lower fertility with chilled semen
Frozen semen
  • Frozen semen requires insemination more closely timed to ovulation because of the reduced longevity of the sperm.
  • Mares are typically palpated every 6 hours and bred as soon as ovulation is detected. Breeding is done after ovulation using frozen semen because the sperm cells undergo capacitation during the freeze/thaw process. This limits their longevity within the mare.
  • If semen supplies are plentiful, bracketing ovulation, i.e. breeding before anticipated ovulation and again after, may be practiced
  • For example, give hCG when a follicle > 35 mm is present, AI 24 and 40 hr later
  • Expect about a 20% reduction in fertility with frozen semen
Mare Management
  • Pre-breeding exam
    • Ultrasonography 
      • Fluid PrebreedingEstimate quantity -  if seems excessive -  vaginal speculum exam, cytology
        • If cytology positive, treat accordingly (antibiotics, lavage) 
        • If cytology negative - oxytocin, lavage, or no treatment
    • Vaginal exam 
    • Culture AND cytology
  • Predicting ovulation
  • Timing insemination
  • Inducing ovulation:  Timing?; Agent?
  • Artificial Insemination
  • Fresh (on farm) semen
  • Fresh (cooled shipped) semen
    • Semen arrival
      • Check motility after warming small sample 
      • Semen inseminated directly into mare 
      • No pre-warming 
      • Inseminate ALL semen received
      • Check concentration
  • Frozen semen
    • Thaw according to directions and inseminate
  • After Breeding
    • Check for ovulation
      • Detecting ovulation
    • Check for fluid
      • Normal mares have fluid up to 6 hrs - Fluid at 12 hrs warrants treatment
      • Fluid post breeding - Treat
      • Note: post breeding, not necessarily post ovulation
      • Oxytocin, cloprostenol, lavage, exercise, + antibiotics if > 24 h

  • Fourteen day pregnancy examination
    • Predict return to estrus 
    • Detect “short cycling” 
    • Detect twins


Breeding Herd (band)

  • Post pubertal mares are 15-18 months and are usually maiden mares (1st time bred).
  • If the mares are less than 5 years old, you can expect about a 75 % foaling rate, but these mares are making their fertility history.
  • Some may be 'hot off the track' and be a handful to breed and may not cycle well for a year.

Foaling mares (wet, lactating, nursing)
  • This is the group with the highest fertility, because they have proven themselves by having a foal at their side.
  • Foal heat is generally around at 9 days postpartum, but may be as early as 5-6 or as late as 12.
Should you breed or not at foal heat ??
  • Foal heat breeding is good in that you can easily detect the estrus, whereas subsequent heats may be harder to detect.
  • Foal heat breeding also keeps the mare foaling earlier in the year, if that is desired.
  • Yes if the mare had a normal foaling and postpartum period (and didn't foal too early n the year).
  • The pregnancy rates on foal heat breeding are dependent on when a mare ovulates postpartum. This is because the mares that ovulate early do not have uterine involution that is as complete, so conception rate is lower.
  • If foal heat ovulation is on day 5-6 postpartum the conception rate is 0%, if it is on day 7-8 postpartum it is about 32%, if it is on days 9-12 postpartum conception rate is about 60%, and if it is grater than 12 days postpartum conception rates run greater than 75%.
  • Conception rates are definitely lower if fluid is observed in uterus on ultrasound examination. Do not breed if fluid is observed.
  • The chances for early embryonic death are not greater if breeding is done on foal heat.
  • The fertility of the next heat cycle is not adversely affected if the mare does not become pregnant.
  • There is no greater chance of infection by breeding on foal heat.
Therapies to enhance fertility of foal heat
  • In order to get better involution you can delay foal heat.
  • Administer Regumate for 7 days to delay the onset of foal heat.
  • Administer progesterone/estrogen. Delaying the first postpartum ovulation by giving 8 days of progesterone treatment improved pregnancy rates (more mares became pregnant when first ovulation occurred after 15 d postpartum (23/28), than when first ovulation occurred before 15 d postpartum (6/12), but the mares become pregnant later than if it was not given.
  • Prostaglandin after foal heat to induce another heat longer after parturition.
  • Prostalene (a prostaglandin compound) BID for 10 d postpartum or until bred, whichever came first resulted in 77% of the treated vs 44% of controls being pregnant after breeding on the first heat. 67% of the treated and 29% of the controls were pregnant after breeding on the second heat.
  • You can also use lights on the pregnant mares to decrease gestation by 10 days, so the mare cycles back earlier. This would be helpful in mares that are due to foal late in the year.
  • Foal heat breeding is a management decision only. The time of year the mare foals is an important aspect. If the foal is born very early, then you may not want to breed on foal heat. If the mare is due to foal late, lights and foal heat breeding may help put her back in sync with your program.

Barren mares
  • Barren mares are those mares that were open the previous year.
  • Whether or not the mares were bred is an important question. A  mare that foaled late and  was held back and simply not bred, is not as big a problem as a mare that was bred a gazillion times and did not get pregnant.
  • Try to determine the reason the mare was barren. Was it an infertility problem, an organic problem (infection, etc.), a cyclic problem, a management problem, or a stallion problem.
  • This is the second highest fertility group because at least they have had a foal, and the maidens have not.
  • Barren mare tend to be harder to get pregnant. Mares are funny in that the more they are pregnant the easier they are to get pregnant. If they are not pregnant for a year or two, they become more difficult to get pregnant.

contributed by Bruce E Eilts and modified on 8 September 2009

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contributed by Bruce E Eilts on 25 September 2012


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