Testis Size and Consistency
As we have discussed, testis size is directly related to the number of sperm produced. More than half the variation in sperm production among stallions can be accounted for by size of testicles. It is important to have measures of testicular width so that the volume of the testis and sperm production can be calculated. Testicular width can be measured with calipers or ultrasonically. Keep in mind however that testicular width increases as you go from the winter in summer. For example, average width of mature stallions was 90 mm in December and 109 mm in July.
In addition to width, the tone of the testes should also be determined. The testes should be firm but not overly hard or too soft. Degeneration of the testis is often noted first by a softness and/or ability to feel ribbing in the testis. Very hard testes can also be an indication that testicular degeneration is occurring from perhaps an inflammatory process (injury or infection).
Unilateral cryptorchid stallions (only 1 testis) should be expected to produce fewer sperm than normal stallions. Cryptorchidism is inherited, these males should not be used for breeding and there use may be discouraged by breed organizations. Males who have only 1 functional testis due to injury however can be used for breeding but should be expected to produce fewer sperm than a normal stallion. If the injury occurred prior to puberty, then the good testis will increase in size larger than a normal testis. The injured testis will then regress to only a fraction of its original size. If the injury occurs after puberty, then the good testis will remain the size of a single testis from a normal stallion. The injured testis of course degenerates and shrinks in size.
Effects of