Stallion Exam
Exam of the Reproductive Tract
External Genitalia - After stimulation of the male to have an erection, all portions of the penis are examined for any evidence of abnormalities, injury or disease. If neccessary, drugs can be used to extend the penis. A genital exam is best done after semen collection, because the stallion will be much calmer. Make sure the penis is free from: Summer Sores (Habronemiasis), Sarcoid, Melanoma or Coital Exanthema (Herpes sores).
Next the scrotum is examined for any evidence of trauma or disease. The testes are palpated to determine general shape and consistency. Include a palpation of the cauda epididymis (tail) to make sure it is enlarged with sperm. A measurement of testicular size should be done and potential sperm production determined. Each testes volume can be calculated as:
Volume =4/3*3.1416* Height/2 * Length/2 * Width/2
or
Volume = 0.5236 * Height * Length * Width
with the measurements in cm. The width for 1 testis is scrotal width/2. The predicted Daily Sperm Output (DS0) is:
predicted DSO = [0.024 * (vol L + vol R)] - 1.26
The DSO should be appropriate for the number of mares the stallion will be expected to breed. Since testicular size is highly heritable, breeding stallions with small testes should be avoided. A common measure of testes size in the stallion is the scrotal width (both testes). Minimal scrotal widths have been suggested for stallions and are shown in the table below:
Total Scrotal Width - Suggested Minimum Guidline |
|||
Age |
2-3 Years |
4-6 Years |
>7 Years |
Minimum |
81 mm |
85 mm |
95 mm |
Range |
81-111 mm |
85-115 mm |
95-124 mm |
Even though we suggest palpation of the scrotum, testes and epididymis after semen collection, for teaching purposes we find it is better to do this on a day when we do not collect semen as the the UW-Madison stallions are more relaxed around a large number of students. We also generally do this in the stallions stall.
