Animal Reproduction-पशु प्रजनन

Scrotal Circumference: Vital For Optimum Fertility in Dairy Bulls

November 13, 2023

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Scrotal Circumference: Vital For Optimum Fertility in Dairy Bulls

Fertility of bull can be defined as ability to impregnate females. Adequate number of genetically superior and fertile dairy bulls are required to cover the breedable females in a herd. Having fertile and healthy dairy bulls in a herd can ensure higher productivity as well as milk production, transmission of desired genetic traits, reduces transmission of diseases and will improves life time fertility of the herd. As per 18th All India Livestock Census (2008), only 10% cattle bulls and 4% buffalo bulls are used for breeding purpose and howmany among them are healthy and fertile is still a question, which needs to be answered. Bull is considered more than half of the herd as the total genetic gain obtained through sire-to-sire path and sire to dam path is about 64 percent. Estimating the breeding value of sires with higher accuracy and the production of a larger number of daughters can make contributions as genetically superior replacement stock for the next generation (Basu, 1996). Unfortunately, not muchemphasis is given to fertility traits as an effective selection tools for genetic improvement among dairy bulls. Prior to put the dairy bulls in a breeding programme, they are generally tested for their phenotypic breeding soundness. Scrotal circumference is one of the most important criteria for breeding soundness evaluation among dairy bull. The largest diameter (cm) of scrotum is taken for breeding bulls using measuring tape. It is to be noted that the testicles of bulls be confined closely in the bottom of the scrotum, so that the measurement should be accurate with highly repeatability. Many researchers have shown that scrotal circumference is an accurate predictor of sperm production in young bulls. Generally scrotal circumference of indigenous and cross bred breeding bulls ranges from 30 to 34 cm (Mukhopadhyay et al. 2010). Reports indicate that increased scrotal circumference is associated with earlier age at puberty, increased semen production and improved semen quality. Scrotal circumference of a bull also provides an important indication of his potential genetic merit for several important fertility traits. According to Sethi et al. (1989) multitude of studies have reported that probability of the bull having satisfactory semen quality increased greatly as scrotal circumference increased from 30 to 38 cm. Scrotal circumference is highly correlated to total sperm output and moderately correlated to normal sperm morphology. Bulls with larger testes will produce more normal sperm cells. Testes size and scrotal circumference has a very high heritability estimate about 0.68 (Latif et al., 2009). This means it is an easy trait to select for and rapid progress can be made in selecting bulls that will produce more normal sperm cells. Selecting bulls with large testes also has a fortuitous spinoff in improving female fertility. Many workers reported that has shown that female relatives of bulls with larger testes reach puberty at a younger age. Increased scrotal circumference also has a favorable relationship with female fertility/ daughter fertility, both in terms of earlier age at puberty, earlier return to oestrous and shorter days to calving (Chacon et al., 2002). Through selecting bulls for testes size as well as growth traits, reduced the age of puberty whereby 80% of the heifers reach puberty by 10-12 months of age and nearly 100% by breeding age at 14-15 months. There is a positive relationship between scrotal circumference and yearling weights so growth traits are not compromised when selecting for both fertility and growth rate. Table (1) illustrates the age wise minimum scrotal circumference (SC) for a bull to pass breeding soundness exam (BSE) in breeding programme, recommended by Society of Theriogenology, 2014.

In the realm of dairy farming, ensuring reproductive success is paramount for maintaining a productive and profitable herd. One often overlooked yet crucial parameter in assessing the reproductive potential of dairy bulls is scrotal circumference. This simple but significant measurement serves as an indicator of testicular development and function, directly influencing fertility. In this article, we delve into the importance of scrotal circumference and its role in optimizing fertility in dairy bulls.

Table 1: Recommended Scrotal Circumference

Age– Minimum SC(cm) –Good SC(cm)

>15 month – 30——–>34

15-18 months–31 ——->36

18-21 months —-32 ——>37

21-24 months– 33 —->38

>24 months—- 34 —->39

There is great variation present in scrotal circumference between different breeds of dairy bulls. Measurement of thousands of English and European bulls have shown that yearling bulls should have scrotal circumference of at least 30 cm and by 20 months of age have a scrotal circumference of at least 32 cm. Brahman breed bulls will have smaller testes at the younger ages and they will reach maturity comparatively at an older age. Brahman breed bulls will have adult scrotal circumferences similar to other beef breeds (Chenowth, 2009). Selecting for genetically larger scrotal size will also select bulls whose daughters reach sexual maturity quicker. Since early maturity is a difficult trait to assess in a commercial situation, an indicator such as scrotal size which is much easier to measure is a valuable tool. Scrotal size correlated with daughters age at maturity, but no reports of correlation with daughters fertility were available. Therefore, we recommend that scrotal circumference is a trait that animal breeders should include in their bull selection criteria.

Understanding Scrotal Circumference

Scrotal circumference refers to the measurement around the widest part of the scrotum, encompassing the testicles. This measurement correlates with testicular size and indirectly reflects the quantity and quality of sperm production. As such, it is a valuable tool for assessing the reproductive capability of breeding bulls.

The Significance of Scrotal Circumference in Dairy Bulls

Fertility Indicator:

Research consistently demonstrates a positive correlation between scrotal circumference and sperm production. Larger scrotal circumferences are generally associated with increased semen quality and higher sperm counts.

Early Predictors of Fertility:

Scrotal circumference measurements in young bulls can serve as early predictors of future fertility. Bulls with larger scrotal circumferences during their development stages often exhibit better reproductive performance when mature.

Semen Quality:

Bulls with larger scrotal circumferences tend to produce semen with superior motility, morphology, and concentration. This directly contributes to higher fertility rates and increased conception rates in dairy herds.

Puberty Onset:

Scrotal circumference is linked to the onset of puberty in bulls. Bulls with earlier puberty generally exhibit better reproductive performance and contribute to the breeding program at an earlier age.

Practical Implications for Dairy Farmers

Regular Monitoring:

Implement a routine scrotal circumference measurement program, especially during the pre-breeding season assessment. Regular monitoring allows for the identification of any deviations or abnormalities.

Age-Specific Guidelines:

Understand age-specific scrotal circumference benchmarks. Young bulls should achieve certain minimum measurements by specific age milestones, ensuring they are on track for optimal reproductive development.

Culling Decisions:

Scrotal circumference can guide culling decisions. Bulls with consistently smaller scrotal circumferences may be less efficient in siring offspring, and culling such individuals can enhance overall herd fertility.

Nutritional Management:

Nutrition plays a vital role in scrotal development. Ensuring bulls receive adequate and balanced nutrition is essential for optimal testicular growth and function.

Health Considerations:

Monitor the general health of bulls, as illness or stress can impact scrotal circumference. Timely veterinary interventions and health management practices contribute to maintaining reproductive vigor.