Equine Science: Reproduction

• ~When it comes to breeding practices and the reproductive process, the mare’s reproductive control mechanisms are quite efficient when left to function in the wild. Manipulation and confinement have reduced the efficiency of reproduction!!!!

3 Fundamental Problems

• Reproductive Anatomy• Long time period before an embryo can safely

implant in the uterus• Variable hormone system synchronizing the whole

process

Stallions….

• Do you remember the parts???• Scrotum divided by the septum• Testes descend through the inguinal canal in last 3

weeks gestation to 2 weeks old• If both testes don’t fall by 2 weeks, the inguinal ring

closes and animal is called CRYPTORCHID (usually left one)

Mating from the Male Perspective• Ejaculation has 3 parts

• Erection• Penis stiffens through

engorgement of blood• Emission

• Strong pulsing contractions• Ejaculation

• Semen expelled

• Controlled by FSH, LH and Testosterone

Sperm Production in the Stallion• Studs start producing semen after one

year, but not fully until 4 (through 20)• Sperm Count….!

• Influenced by season, testicular size, age and frequency

• Constant production, but seasonal breeders

• May/June/July • Sept-Feb testes are regressed and sperm

count is down…WHY?

Can you change a low sperm count?

• If it is because of season…yes….HOW?• Can use artificial light (16-8)• Causes early “burn out”

THE MARE….

• Review Parts….

The Mare….

• Some problems…• Simple uterus with unusual placenta attachments…

inefficient cervical closure and very small uterine body with long, narrow horns

• Elongated shape of uterus/horns causes inefficient drainage (infection!!) and with each pregnancy, the connective tissue decreases in tone and uterus hangs lower and lower!

Mare…

• The cervix is controlled by hormone levels and tends to not seal…leading to embryonic death

• Placenta is attached to uterus by villi• Shallow, 1 cell thick attachments• Lets no immunoglobulin pass to fetus

• Antibodies from mare to foal• Any cell shedding endangers life of fetus

AND…

• Any hormonal imbalance leads to problems with cycling, maintaining a pregnancy, delivering a foal and adequate milk supply…..

Hormone Cycles

• Luteal Phase: When the CL is producing • FSH …..Follicle• LH….CL• Estrogen…estrus• Progesterone…pregnancy

• What causes the CL to regress if there is no pregnancy?• Prostaglandins

Quiz Questions

• 1. FSH stands for?• 2. LH stands for?• 3. Canal the testes descend through.• 4. Where the urethra drains in the mare

(reproductive part)• 5. Phase when CL is producing hormone• 6. Hormones that cause CL to regress

• What does FSH do?• Levels must balance or mare will cycle again, killing the

first embryo!

• Seasonally Polyestrous• Cycle several times, not usually all year round• Peak month is June

• Start irregular cycles in Jan/Feb…irregular again by Sept/Oct• Early foals

• Breeders want early or spring foals…the mares need to be bred at a time that is not “normal” and thus causes INEFFICIENT reproduction

• Even the heat length changes! • 6-8 days initially….3-4 during peak• Variation is the rule…not the exception!

• Some mares show estrus without ovulating

• Some mares ovulate without showing estrus

• If all else fails…go for JUNE!

The truth about the CL…• After ovulation the “hole” fills with a

blood clot…• Corpus hemorrhagicum• This later becomes the CL

• Which hormone does the CL secrete?• Why is it referred to as the Yellow Body?

Long, difficult labor is called…• Dystocia• Twins are very rare due to

• High abortion rates• Dystocia

• Long, difficult labor• Retained placenta

More Mare Problems!

• If mare aborts before day 45….• She continues to think she is pregnant until day

120!....that is 4 months!

• Takes a LONG time for embryo to attach!• 16-18 days it floats around!

• Horse embryos are not more fragile than other species; it’s primarily that horses in general have poor reproductive performance (ability to maintain a conceptus). There are many causes of early embryonic loss. Stress, fever, uterine infections, hormone abnormalities and twins can all cause a mare to spontaneously abort. The egg is fertilized in the fallopian tubes and does not enter the uterus until about Day 6 of gestation. Once the embryo descends into the uterus, it has to traverse the entire uterus to be recognized by the mare. If the embryo does not touch all portions of the uterus by day 16 of gestation, the mare will reject the embryo, and begin showing signs of estrus to begin the next “heat” cycle. If the mare does recognize the presence of the embryo, then the embryo will attach itself to the wall of the uterus on or about Day 17.

• Mares are pregnant 335 days (+, - 2-4 weeks)Abortion: loosing fetus before 300 daysStillbirth: loosing fetus after 300 days

• After several foals, there are changes in the vulva and vagina causing pneumovagina (air in vagina) and urine pooling

• Mini and large breeds have even MORE problems• Strong athletes may not produce at all• Pain due to cardiac, laminitis, tendonitis may not

breed

• Colostrum is VERY important because no antibodies transfer to foal….BUT mares tend to loose colostrum when they “bag up”

• You need to collect the colostrum if that happens!• If hormones don’t balance, they may not produce

milk (fescue grass)

Signs of Birth

• Large, pendulous abdomen, 10-11 month

• Udder enlargement • Calcium in milk can

predict foal arrival time• Waxed teats• Relaxation of tail head and

area • relaxin

• Enlarged milk veins• Loss of appetite (not all)• Change in personality• Separate themselves• Push hind against wall• All MARES are different!

LABOR!!!!

• Intense and rapid• Usually over in an hour

• Because of short time, you NEED to be there!• Some mares have a CASLICK to remove

• A suture closing the vulva to prevent infection

Definitions of the Placenta

• Amnion:• The inner-most membrane

• Chorion:• The outter-most membrane

• Placenta:• Organ formed in the uterus• Moves nourishment from the mother's blood to fetus• Sends the fetus's waste products into the mother's blood to be

disposed of by the mother's excretory system• Fetus is attached to the placenta by the umbilical cord

Labor….• Stage One

• Ends when ALANTOIS (fetal membranes appear and AMNIOTIC FLUIDS break) water breaks

• Stage Two• Intense labor with contractions pushing foal• Fetus is in white, filmy amniotic membrane• Foal is born (if not in 45 min…big problem!)• Placenta is still attached inside, providing oxygen

• The amnion is completely free from the chorion in mares and is not indirectly tethered to the uterus as it is in cows. Therefore, the amnion does not rupture early in the birth process and a foal can be born with the amnion covering its head. Unless the amnion falls off as a result of movement on the part of the foal or mare, or is removed by an attendant, the foal may suffocate.

                                              

                                                                                                                

 

Labor….

• Stage 3• Placenta (thick, pink) and fetal membranes are expelled

• ~”Prior to being passed, the placenta hangs from the vulva. It should be tied up so that the mare does not tear it or become afraid of it”

Labor….

• DON’T EVER pull the placenta out!• Physiologically released• Can cause uterine infection (metritis) which leads to

laminitis or death…if symptoms show, it is too late!

• Involution within 10 days• Foal heat (conception not recommended and is unlikely)

After Labor….

• Feed bran, beet pulp or other laxatives…WHY?• Makes defecation less painful

• Bad smells indicate postpartum infection• Some mares don’t ovulate during lactation

THE END…..