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Examination of the stallion and semen assessment
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Summary
Evaluation of the reproductive system in a stallion for a fertility examination should assess whether he has the physical and mental faculties necessary to deliver semen containing viable spermatozoa and no infectious disease to the mare's reproductive tract at the proper time to ensure establishment of pregnancy in a reasonable number of mares mated per season. The evaluation needs to assess libido, mating ability, any congenital defects that may be transmissible to offspring as well as quality of semen ejaculated. The results of the examination should be recorded in a systematic and accurate manner.
Stallion handling and semen collection requires a high level of skill in order to attain good results and in safety. The most important person in the collection process is the stallion handler; if he is not in control of both the stallion and the whole event this will put everyone else in danger. Preparation beforehand is essential especially if you are going to an on farm collection and using people that have little or no experience in the semen collection procedure. They may well have carried out many natural coverings on the stud but with no AI collections involving an extra person doing the collection.
When you go onto their premises here are a few question worth asking.
Is there a GOOD teaser mare in season?
Where is the collection going to take place?
Where are you going to set up a lab?
What is the health status of the stallion?
Health and safety?
Identification
Accurate and detailed identification of any stallion which is the subject of a fertility examination is vital. Name, age, breed and the colour and markings should be checked against a passport. This description should be included in the report.
History
As detailed a history as possible should be collated. Historical information important to a fertility examination includes his breeding, present use (performance, racing or breeding) results of previous fertility examination, body condition, illnesses, injuries, any drugs administered and vaccinations. Important historical reproductive information includes the number of mares mated each season, the number of pregnancies, the fertility of the mares he mated and the performance of any other stallions on the stud farm. If the stallion is an active breeding animal it is important to know the frequency with which he was being used and the last time he ejaculated. The best measurement of a stallion’s fertility can be made by examining the pregnancy and foaling rate of a large number of mares bred to that stallion under optimal conditions. However, this is not always available and is in any case not available for some 9 to 12 months during which time his fertility can change.
Physical examination
Evaluation of the general body systems is an important part of the examination. Deficiencies in the general body systems such as lameness, breathing problems or impairment of sight can affect fertility and use as a breeding stallion. The stallion’s freedom of movement, general body condition and temperament should be noted. Any signs of lameness, muscle wastage or back problems should be recorded and any potentially heritable defects such as cryptorchidism, parrot mouth or wobbler syndrome noted. It is important to note any heart abnormalities.
Physical examination of reproductive tract
External genitalia
The urethra, penis and prepuce should be routinely examined thoroughly by direct manual palpation and any palpable or visual lesions recorded. Where problems are suspected, ultrasound and endoscopy may also be useful. The scrotum and its contents (testes and epididymes) should be palpated in their entirety. The scrotum should be thin and elastic with a distinct neck. The skin is smooth and hairless and any lesions in the scrotal skin should be noted. The testicles in the stallion are located horizontally and both testes and epididymes should be of the same size and freely moveable. The prominent tail of the epididymis is located on the caudal pole of the testicle. The testes should be oval, smooth and regular with a slightly turgid texture. Flabby or hard testes are potentially poor producers of sperm. The position of each testis within the scrotum can be determined by palpation of the epididymis. Rotation of the testis through 90' to 180' can occur with no clinical signs and no apparent effect on fertility. Measurements of the length, width and height of each testis are made along with total scrotal width, using callipers or ultrasonography. Total scrotal width of mature, fertile stallions should be greater than 8 cm. Testicular size is highly correlated with daily sperm output (DSO). If the number of sperm collected does not approximate with the calculated number of sperm produced by the testes of a given size, this may suggest non-representative semen samples or testicular degeneration.
Internal genitalia
Examination of the internal genitalia is difficult unless suitable examination facilities are available and the veterinary surgeon is experienced in what to palpate. The internal genitalia can be examined by manual palpation and or ultrasonography per rectum. The size and consistency of the internal genital organs should be noted.
Assessment of libido
Sexual behaviour should be evaluated by bringing the stallion into contact with a mare in oestrus and the reaction of the stallion to the mare should be noted. The intensity of the reaction also known as libido is dependent on mating experience, management and in some cases on season. Typically a normal stallion that has never mated a mare will take a longer time to mount, however, he will display good libido. On the other hand a stallion that has had a negative previous experience might show no interest in the mare or in mounting. A normal stallion should show interest in the mare, and drop the penis within 1-2 min of exposure to a quiet mare in standing heat. He should gain an erection and will try to mount within the first 3 min. Once he has mounted properly he should have several (5-8) intravaginal thrusts, followed by 3-5 short thrusts synchronous with ejaculation, urethral pulsation and flagging of the tail. He should not withdraw before ejaculation is complete. Before a stallion can be considered a satisfactory breeding prospect he must be able to copulate normally i.e. he must develop an erection, mount without hesitation, insert the penis, provide intravaginal thrusts, and ejaculate.
Equipment required to carry out a successful collection
- Artificial Vagina
- Disposable Liners
- Semen Filters
- Collection Bottle
- Lubricant
- Disposable shoulder length gloves
- Dummy Mare (optional)
Evaluation of semen
Semen should be collected into a pre-warmed container, and should be maintained at body temperature while in its raw state. Semen that is collected for artificial insemination purposes should be filtered to remove the gel fraction and diluted with an appropriate pre-warmed extender. The physical characteristics of the ejaculate, including volume, concentration, colour and motility should be evaluated.
To enhance its reliability, an experienced person in a properly equipped laboratory should perform a semen evaluation in a thorough, methodical manner. Routine tests include:
- volume of gel-free semen
- volume of gel
- colour
- pH determination
- percent and type of motility in raw and extended semen immediately after collection
- longevity and character of motility in raw and extended semen
- sperm concentration
- morphology
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