Equine Reproduction

Dr. Jack Sales, DVM

 

 

 

LESSON ONE

 

 

Anatomy and Physiology of the Stallion

 

                                                           

Required reading:  Manual of Equine Reproduction by Terry Blanchard.  This book is available through the HCOL College Bookstore.

 

 

This lesson does not have a corresponding chapter associated with it. No reading assignment will be given in lesson one.

 

EQUINE REPRODUCTION – TERMS AND FACTS

 

 

Introduction of Terms and Facts

 

          During this course you will be exposed to many new vocabulary words that are commonly used in the breeding industry, but with which you may not be familiar.   It is important you have a working knowledge of these terms in order to more efficiently function in an equine breeding environment.

 

Stallion Terms

 

Anabolic steroid or hormone: Androgenic hormone derived from testosterone.   Aggression and increased libido.

 

Breeding roll: Usually made as a roll of cotton on a pole which is placed between the mare’s hind quarters and the stallion (above the penis) to prevent the stallion from deep penetration during breeding. (maiden mares, mares with caslicks)

 

Bull Pole: A sturdy pole that can be fastened to the halter to keep an aggressive stallion from crowding the handler.

 

Cryptorchid:  A male horse in which one testicle is retained in the body cavity.

 

Ejaculation:  Emission of semen from the penis.

 

Flaccid: Refers to a non erect penis in the stallion.

 

Flehman:  Common behavior pattern consisting of curling and raising of the upper lip indicating sexual stimulation in the stallion.

 

Libido:  Sexual drive or desire.

 

Scrotum:  Pouch that contains the testicles.

 

Spermatogenesis:  Development of mature sperm cells which occurs within the testicles.

 

Stallion ring:  Rubber or plastic ring secured behind the glans penis of the stallion that discourages stallion erection.

 

Teaser:  A male horse used to detect estrus (heat) in mares.

 

Vasectomy:  Operation in which the vas deferens is cut to prevent passage of sperm from the testicle into the male repro tract.

 

 

 

Broodmare Terms I

 

Abortion:  Expulsion of the fetus from the uterus between 30 and 300 days of gestation.

 

Early embryonic death:  Expulsion of the embryo or absorption of the embryo from conception to 30 days of pregnancy. (absorption or resorption)

 

Afterbirth:  Expelled placenta.

 

Agalactia:  Absence of milk in the udder after foaling.

 

A.I.:  Artificial Insemination.

 

Anestrus:  Period of sexual quiescence.  No estrous cycle.  Winter months.

 

Cervical os:  Opening of the cervix.

 

Conception:  The meeting of the sperm and the ovum to form the embryo. In the mare this occurs in the oviduct.

 

Fertilization:  The union of the sperm and the ovum.

 

Gestation:  Pregnancy.

 

Hymen:  The thin membrane that partially covers the external vaginal opening, found in maiden mares.

 

LH:  luteinizing hormone. – Causes follicle ovulation and formation of CL

 

Luteolytic:  Causing the lysis or degeneration of the CL. (prostaglandins)

 

Maiden:  A mare that has not been bred.

 

Ovulation:  The release of the ovum (egg) from the mature follicle.

 

Silent heat:  Estrus period in which the mare ovulates, but fails to show behavioral signs of heat.

 

Speculum:  Instrument for enlarging the opening of a cavity as in vaginal speculum.

 

Transition phase (transitional anestrous):  The period that occurs at the beginning of the breeding season, marked by erratic estrous cycles.

 

Winking:  A behavioral sign from a mare in heat, turning and lifting the tail and everting the vaginal labia to expose the clitoris.

 

 

Broodmare Terms II (The pregnant mare)

 

Gestation period: 11 months and 7 – 11 days.

 

Days in estrus (heat):  5 days

 

Ballottement:   A method of pregnancy diagnosis in which the uterus is tapped through the rectum or flank and the fetus can be felt bouncing back against the hand.

 

Breaking water:   Expulsion of fluids from the uterus prior to the foal being passed.

 

Breech birth:  The hindquarters are presented first during foaling.

 

Breeding stitch:   Heavy suture placed at the lower end of the caslicks’ suture line to reinforce the suture line during breeding.

 

C section:   caesarean section –Surgical removal of the fetus.

 

Dystocia:   Abnormal or difficult birth.

 

Endometrial cups:   Raised structures formed at about day 36 of pregnancy and responsible for progesterone release and maintenance of pregnancy up to 120 days.

 

Foal heat:   The first heat or estrus period after foaling (9-day heat).

 

Hobbles:   Device used to restrain an animal by restricting leg movement.

 

Involution:   In the mare, the process by which the uterus returns to the normal state after pregnancy.

 

Kicking Boots:   Padded boots sometimes placed on the mare’s back feet to reduce any blow sustained by the stallion during breeding.

 

Lactation:   The period of milk production.

 

Palpation:   Feeling by the sense of touch – rectal palpation of ovaries and uterus.

 

Placenta (afterbirth):   Tissue which surrounds the fetus during pregnancy. It is connected to the fetus by the umbilical cord and serves as the structure by which the fetus receives nourishment from and eliminates waste matter into the maternal circulatory system.

 

Postpartum:   Pertaining to or after the birth of the foal.

 

Resorption:   The absorption of an early pregnancy – Early embryonic death.

 

Retained placenta:    Afterbirth that is not expelled within 4 to 6 hours after foaling.

 

Stillbirth:   the birth of a dead fetus.

 

Waxing:   Formation of beads of dried colostrums at the ends of the teats.

 

 

 

 

Hormones Associated with Reproduction

 

Hormone

Primary Production site

Target organ

Effect

Therapeutic use

Estrogen - Heat hormone

Ovary (ovarian follicle)

Uterus, cervix, and external genetalia of mare

Expression of estrus. Female sex characteristics, genital tract changes

Enhances estrus (heat) but may interfere with normal cycling.

Progesterone -Pregnancy Hormone

Corpus luteum of ovary (CL) also the placenta during pregnancy

Uterus

Mammary gland

Maintains pregnancy

Prevent abortion. Synchronize or suppress estrus (regumate)

 

Prostaglandin

Uterus

Corpus Luteum (CL)

Luteolysis.(CL regression)

Synchronize estrus. Treat persistent CL.

Gonadotropin releasing hormone (GnRH)

Hypothalamus

Pituitary gland (master gland)

LH and FSH release

 

Follicle Stimulating Hormone(FSH)

Pituitary gland

 Ovary-mares

Seminiferous tubules-male

Growth of follicle-mare spermatogenesis-male

Same as effect

Luteinizing Hormone (LH)

Pituitary gland

Mature follicle–mare

Leydig cells –male

Follicle maturation and ovulation

Stimulates testosterone production

Same as effect. (gonadotropin(HCG)

Oxytocin

Pituitary gland

Uterus , mammary gland

Uterine contraction, milk let down

Retained placenta elimination, induce abortion or foaling

Prolactin

Pituitary gland

Mammary gland

Milk production

 

Relaxin

Ovary, placenta

Pelvic tissues

Relaxation of pelvic area for foaling

 

 

 

The Foal and Foaling Mare terms

 

Agalactia:   Absence of milk in the udder after foaling.

 

Colostrum:   The first milk of the mare rich in protective antibodies.

 

Congenital:   Existing at and usually before birth.  May or may not be inherited.

 

Coprophagy:   Manure ingestion.

 

Feral:   Not domesticated.

 

Fetus:   The unborn foal from 40 days to birth.

 

Foal heat diarrhea or scours:   Diarrhea that usually occurs in foals during the mares foal heat.

 

Gonad:   Organ that produced gametes (testicles or ovaries).

 

Live foal guarantee:   Stallion contract provision that guarantees the mare owner a live foal as a result of the purchased breeding. The guarantee usually gives the mare owner the right to rebreed the next season to the same stallion.

 

Meconium:   The first fecal passage of the newborn.

 

Neonate:   Foal less than 3 or 4 days of age.

 

Nurse mare:   A mare selected for mothering ability and bred each year for the purpose of raising orphan foals.

 

Suckling:   An unweaned foal.

 

Urachus:   Small vessel in the umbilical cord that connects the fetal urinary bladder to the outside.

 

Weaning:   To permanently deprive of milk.

 

Early embryonic death:    Expulsion of the embryo or absorption of the embryo from conception to 30 days of pregnancy. (absorption or resorption).

 

 

The Infected Mare

 

Agar:   Culture media used for growing bacteria.

 

Barren:   A mare (other than a maiden mare) that did not become pregnant during the last breeding season. (Dry mare).

 

Caslicks operation:   The process of stitching the upper 1/3 to ˝ of the vulvar lips together to prevent wind-sucking ( the sucking of air or contamination into the reproductive system of the mare.

 

Culture and sensitivity:   Taking of a swab from the uterus of the mare and attempting to grow bacteria to determine infection then subsequently determining to what antibiotic the growing bacteria will be sensitive. (would be effective in combating the infection).

 

Endometritis (metritis):   Inflammation or infection of the uterus.

 

Fertile:   Able to produce offspring.

 

Gonadotropin – gonadotrophic:   A hormone that promotes gonadal growth and function.

 

Impotency:   In the stallion, the reduced ability, inability, or lack of desire to breed.

 

Infertility:  In the stallion - the reduced ability of the sperm to fertilize the ovum or the reduced ability of the stallion to produce sperm.  In the mare - the reduced ability or inability of the mare to conceive or carry a foal to term.

 

Metritis:   Inflammation or infection of the uterus.

 

Open:  Not pregnant.

 

Resorption:   The absorption of an early pregnancy – Early embryonic death.

 

 

 

Artificial Insemination and Embryo Transfer

 

A.I.:   Artificial Insemination.

 

AV:   artificial vagina – Used to collect semen from the breeding stallion.

 

Autoclave:   Sterilization device that uses pressurized steam to sterilize instruments.

 

Catheter:   Hollow cylinder designed to introduce fluids into a body cavity.

 

Condom:   Sometimes used for collection of semen from the stallion.

 

Dismount sample:   the portion of the stallion’s ejaculate which trickles from the penis immediately following dismount from breeding.  Sometime used for semen evaluation although not very reliable.

 

Donor mare:   The mare which donates an embryo for embryo transfer. (The more valuable mare).

 

Recipient mare:   The mare receiving the donated embryo to carry through pregnancy to term.

 

Embryo:   Considered to be the union of the sperm and ovum up to 30 to 40 days of pregnancy.

 

Embryo Transfer:   A method whereby a developing embryo is removed from its natural mother and implanted in the uterus of a host mother for the remainder of pregnancy.

 

Estrous synchronization:   Process by which two or more mares are synchronized so they come into heat (estrus) at the same time. Used most often in embryo transfer, prostaglandin  or progesterone (regumate) is the drug used most effectively for this process.

 

Extender:   Liquid formula used for semen dilution and longevity.

 

Hemospermia:   The presence of blood in the semen.

 

Phantom or dummy mare:   A raised, padded support that is mounted by the stallion for semen collection.

 

Semen:   The ejaculate comprised of sperm cells and secretions of the testes and accessory sex glands.

 

Spermicidal:   A substance that would inactivate or kill sperm cells if that substance comes into contact with semen.

 

Sperm rich fraction:   That portion of the ejaculate which contains 80-90% of the ejaculates total number of sperm.

 

 

 

 

 

 

The Stallion Reproductive System

 

 

I.             Anatomy & Physiology (structure and function of the stallion reproductive system).

 

a.    External Genitalia

1.   Testis (Testicles) (2) – Are found within the scrotum, and have a dual function. The testicles are considered both an exocrine gland (produces a cellular component that is transferred through a duct system) and an endocrine gland (produces a hormone that is absorbed through the blood stream and carried throughout the tissues in the circulatory system.) The exocrine function of the testicles is the production of sperm cells. Sperm cells are produced within the testicular tissue and require a slightly cooler environment that normal body temperature. The scrotum acts as a thermo regulator in that it is able to keep the testicles away from the body and therefore the temperature of the testicular tissue is conducive to the production of live sperm cells. The cremaster muscle, which attaches to the each testicle is also a part of the thermoregulatory system and can contract and pull the testicles up closer to the body during colder weather, and relax and drop the testicles further from the body in warmer weather, thereby guaranteeing live sperm production. The pampiniform plexis, a convolution of blood vessels supplying the testicular tissue with blood, is also part of the thermoregulatory system, in that it cools the blood going to the testicles. The endocrine function of the testis is the production of the male hormone testosterone. Testosterone, the male hormone, initiates sperm production and development and maintenance of masculine characteristics and is also responsible for the libido (sex drive or sexual desire).

 

       The Epididymis connects the testicle to the vas deferens.  The

       epididymis is where sperm is stored.  The vas deferens (deferent

       duct or ductus  deferens)  is the channel by which the sperm are 

       transported from the epididymis to the urethra during ejaculation.

 

       The Urethra is surrounded by the Penis and is responsible for

       transporting sperm to the mare’s reproductive tract.

 

    The Prepuce (sheath) surrounds and protects the penis.

 

          Other internal sexual organs of importance are the accessory sex glands (Seminal Vesicles, Bulbourethral gland, prostate gland and the ampulla) which  add fluid volume and nourishment to the sperm cells. (Pre-ejaculate, ejaculate, gel fraction, tail end fraction of a semen sample)                          

 

 

            

Here students at an Equine-Reproduction.com course watch as a ground collection is demonstrated.

More details of this technique can be found in the article at
http://www.equine-reproduction.com/articles/ground_collection.shtml

Photographs are used with permission of Equine-Reproduction.com LLC and may not be reproduced.

 

          Erection and ejaculation are brought on by psychic stimulation of the brain usually brought on by a mare in heat.  Here students collect a stallion.

b.   Penis engorges with blood which causes a rigid penis with an increase in length of about 50%.

c.    Ejaculation – expulsion of semen from the penis. Ejaculation consists of about 10 pulsations that occur at approximately one second intervals. About 75% of the total sperm is present in the first three to four spurts of fluid.

 

          Puberty (attain the ability to breed a mare) usually occurs in the light breed horses of North America at about 18 to 24 months. Puberty refers only to the presence of aggressive sex drive and ability to produce mature sperm. The stallion does not achieve full reproductive maturity until about 4 years of age.

 

Testosterone caused male sex characteristics include:

1.  Increased muscling of the neck, head, shoulder  

     and back.

2.   Closure of growth plates of the long bones (epiphysis).

3.   Onset and maintenance of normal sex drive.

4.    Sperm production.

5.    Sex drive (libido) and aggressiveness. (Flehman  response – curling of the upper lip).

 

 

Sex drive is an inherited trait that determines how quickly the stallion can be trained for breeding shed procedures, and also determines how stable his behavior will be after training. The act of breeding, in contrast, is a trial and error - learning process.

 

A stallion “teasing” a mare.

 

 

 

The individual sperm anatomy

            i.    Head, neck piece, mid piece, tail.

           ii.    Must be seen microscopically in the horse to determine normal anatomy and motility. (Motility of bull semen can be determined without a microscope.)

 

 

          We will go into greater detail and study of sperm cell anatomy and physiology in the lesson on Artificial Insemination.

 

Stallion Management

 

I.            Stallion Selection -

a.    Genetic potential – quality traits that can be passed on to his offspring.

b.   Willingness to cover mares and physical ability to settle them. (Individual libido and fertility.)

 

II.          Reproductive Exam

A.   Experienced veterinarian or equine reproduction specialist.

1.   Overall general health exam.

2.   Medical history.

3.   Disposition (libido).

4.   Physical exam of reproductive anatomy.

5.   Physiological exam involving observation of the breeding process as well as semen evaluation.

a.    Volume of semen per ejaculate.

b.   Concentration of sperm in semen.

c.    PH of semen.

d.   Motility of sperm cells.

e.    Morphology of sperm cells.

f.     Live – dead percentages.

g.    Longevity.

h.   Contamination (wbc’s or rbc’s present).

 

 

Normal Semen Parameters

Volume 30-250 ml.

 

Concentration – 30-600 million (10 to the 6th) /ml.

PH – 6.9 to 7.8

 

Morphology – at least 65% normal.

 

Live/dead count – at least 65% live cells.

 

Motility – at least 40% actively motile (moving in a straight line).

 

Longevity – at least 40-50% live after 3 hours at room temperature; at least 10% live after 8 hours at room temperature.

 

 

III.        Stallion Vices

A.   Vices dangerous to the handler or mare:

1.   Overly aggressive behavior (savaging mares or handlers).

2.   Biting (muzzle or protective leather pad for mare).

3.   Rearing and striking (nose chain or lip chain).

B. Vices dangerous to stallion.

1.   Self mutilation (muzzle or neck cradle; increased exercise or companion.)

2.   Cribbing and windsucking (cribbing strap).  A diet with no long stem roughage can lead to wood chewing.

3.   Weaving and stall walking (exercise or obstructions in the weaving or walking path and/or a companion).

 

    C. Vices detrimental to breeding.

 1.  Slow breeder (need for extended stimulation for erection and mounting or repeated mounts to ejaculate).

a.    Improper breeding training.

b.   Abusive or rough handling.

c.    Overuse of the stallion.

d.   Prior bad experience in the breeding shed.

2. Masturbation

a.    Boredom – exercise or prevent the isolation of the stallion.

b.   Stallion ring or wire brush on belly.

 

 

IV.         Proper Stallion Management

A.   Nutrition.

B.   Exersise.

C.   Housing.

D.  Health care.

1.   Dental care.

2.   Preventive medicine.

E.   Hoof care.

 

 

 

Normal Breeding Behavioral Parameters

 

Number of mounts per ejaculate – 1.5

 

Average time to mount-- 5 seconds to 3 minutes.

 

Average time to ejaculate-- 20 seconds to 1 minute.

 

Breeding  time (from onset of sexual stimulation to completion of breeding) – 45 seconds to 5 minutes.

 

Number of covers per season—40

 

Percentage of mares pregnant-- 65 to 90%

 

Percentage of mares actually foaling – 45 to 80%

 

 

Stallion Infertility

 

 

DEFINITIONS:

 

Infertility:  reduced ability of stallion to impregnate a mare.

 

Sub-fertility:   same as above.

 

Sterility:   complete and permanent loss of the sperm’s fertilizing capacity or of the stallion’s ability to produce sperm.

 

Impotency:  term used to describe the stallion’s reduced ability, complete inability, or lack of desire to perform the breeding act.

 

 

Causes of Infertility in the Stallion:

 

I.             Drugs

a.    Testosterone and /or anabolic steroids.

1.   With long term or excessive use these drugs will inhibit the normal negative feedback system in such a way to inhibit the normal production of Interstitial Cell Stimulating hormone (LH) and Spermatogenesis Stimulating Hormone (FSH) which will in turn cause a reduction in sperm output, sperm motility, and testicular size.

b. Other drugs, especially ones causing severe side effects such as diarrhea, loss of

    appetite or an allergic reaction, could be a cause for infertility in the stallion.

 

II.           Overuse

a.     Overuse is a potential cause of infertility and impotency.

1.   Young stallions are more prone to overuse.

 

Daily breeding in the average, aged stallion will lower the concentration of the stallion sperm per ejaculate, but should not lower the total number of sperm produced per day. (Generally leads to higher volume of sperm, with fewer sperm per milliliter of semen).

 

Every other day breeding in the average, aged stallion will not decrease the concentration of the sperm produced at each ejaculate.

 

In an A. I. operation, every other day collection is ideal.

 

In live cover operation with full book of mares, although it depends on the individual stallion, the average, aged stallion should be bred no more than 6 – 8 times a week.

 

 

III.         Painful Breeding

A.   Injuries to the limbs, especially hind limb problems (hock or stifle lameness’s) may cause the stallion to hesitate or refuse to breed.

 

Medication and/or corrective shoeing may be necessary to manage the injury.

B.   Painful problems associated with the reproductive organs. Injuries to the penis.

 

Care must be taken when using stallion rings, and when washing and handling the penis before and during breeding and collection.

 

C.  Excessively rough handling of the stallion, or an uncooperative mare.

1.   Behavioral problems must be addressed efficiently and without causing more behavioral problems.

 

IV.         Season of the Year

A.   Stallion is also affected by length of daylight.

1.   During the fall and winter months the stallion will have a longer reaction time, longer time from initial sexual stimulation and mounting, and will have a greater number of mounts required per ejaculation. (Libido decreases during this time).

2.   Semen quality will be slightly less during this time.

 

V.           Genetic Aspects

A.   Behavioral as well as physical characteristics for sufficient breeding ability or potential is genetically endowed.

B.   Hormonal abnormalities can be genetically endowed.

C.   Cryptorchidism –Failure of one or both of the testes to descend into the scrotum.

 

VI.         Diseases

A.   Hereditary disease associated with the reproductive organs.

B.   Testes.

1.   Orchitis –infection or inflammation of the testicle can be caused by a number of infectious diseases.

2.   Tumors – can occasionally affect one or both testicles.

3.   Trauma by physical blow (mare kicking) will affect fertility negatively.

C.   Penis

1.   Irritation or localized infections could be a problem.

2.   Tumors (melanoma, or squamous cell carcinoma) will affect fertility negatively.

 

D.  Urethra

1.   Infection can be introduced from an infected mare into the stallion’s urethra and cause the stallion to become infected. This infection can travel to the accessory sex glands, the vas deferens, the epididymis and the testicle itself.

a.    A healthy stallion can usually resist this infection from becoming permanent, but will be able to transmit to other mares during live breeding or A.I. until his immune system clears it from his system.

 

VII.       Trauma

A.   Physical trauma to the external genitalia is probably the most common problem seen in the stallion causing a temporary infertility or impotency during the breeding season.

1.   Breeding shed accidents.

a.    Best prevented by good management and anticipation of possible problems. Use of hobbles, routine breeding shed activities, proper stallion handling)

b.   Penile hematoma –

1.   Blow to the penis or bending of the penis while it is erect will cause a rupture of the blood vessels within the tissues of the penis.

 

VIII.     Semen Abnormalities

A.   Volume – normally not a critical issue with fertility. Concentration (number of sperm per ml. of semen, is the determining factor in fertility of the stallion). 

B.   Color – Blood in semen renders the semen useless. (Blood or pus in the semen causes infertility). Pus may also discolor the semen, and would indicate infection within the reproductive tract.

C.   Density – Semen that is too thick and gelatinous or to thin and watery indicates malfunction of the accessory sex glands.

D.  Motility – If collection and handling techniques did not cause the reduced motility, some problem within the stallion is to blame. This would cause infertility if found to be less than 50% progressively motile sperm in the sample.

E.   Longevity – If not caused by collection and handling techniques reduced longevity of the sperm will reduce the sperms chances of fertilizing the mare’s ovum.

F.   Morphology – Abnormal sperm cells. Semen samples that contain less than 65% normal sperm cells are directly related to reduced fertility.

G.  Live/Dead Percentage - If a semen sample contains less than 60% live cells in a fresh sample, fertility may become affected.

H.  Sperm numbers – The reduction in the number of viable sperm cells per ejaculate may be due to seasonal variation, overuse, testicular degeneration, or increased testicular temperature. Sperm Concentration normally ranges from 30 million to 600 million sperm per milliliter, and at least 100 million progressively motile sperm are needed for acceptable conception rates. The average concentration of a stallion is 50 – 250 million per ml.

I.     PH – An increase in the semen ph (normal is 7.0 –7.8) may be caused by presence of urine or by infection within the reproductive tract, or by overuse.

J.   White blood cells – Although some white blood cells may be found in a semen sample, a greater than 1500 WBC per cubic milliliter) usually reflects infection within the reproductive tract and infertility.

 

 

 

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