Improving female fertility is difficult since most traits associated with female reproduction have low heritability. On the other hand, male reproductive traits are moderately heritable.
Scrotal circumference is often used as a direct measure of male reproductive performance.
Scrotal circumference is reliable, inexpensive and able to be utilised on large numbers of animals. It is used as an estimate of total spermatic volume.
Increased scrotal circumference is well correlated with total spermatic output and younger age at puberty. Increased spermatic output increases conception rates, especially in high ewe-to-ram numbers. Younger age at puberty means rams may be assessed and used at earlier ages. Scrotal circumference may be weakly involved with libido (associated with increased testosterone) and spermatic quality.
Provided male traits are well correlated with female reproductive traits, male traits may be used to estimate potential female performance.
Scrotal circumference is correlated with female reproductive traits and so is used as an indirect measure of female reproductive performance. Similarly to ram lambs, increased scrotal circumference is correlated with younger age at puberty of daughters. Younger age at puberty provides the opportunity to join ewes at an earlier age and ensures regular cyclicity at joining.
Scrotal circumference is also well correlated with live weight. Increased live weight has a positive impact on both fleece weight and kilograms of saleable lamb.
Producers should utilise measures of scrotal circumference to identify superior rams to improve flock fertility and genetic gain (and reduce number of rams required). Evidence suggests selection of rams with higher scrotal circumference will improve flock fertility and production.
Rams with scrotal circumference less than 30cm (measured at 10-16 months) should not be used.
Scrotal circumference is assessed as part of a breeding soundness examination, conducted by a veterinarian. Palpation of the testicles may identify issues, including cryptorchordism, orchitis, epididymitis (which may be indicative of Brucellosis), neoplasia or trauma, all of which will affect reproductive performance.
Harry Roach BVetBiol/BVetSc (Hons)