Summary: Bull breeding soundness exams are our best method to determine the potential fertility. However, the evaluation can have may draw backs including a very subjective nature, use of cheap evaluation equipment (especially the microscope), no specific processes to help create consistent results, bull producer pressuring veterinarians to “pass” bulls or using the cheapest providers who pass the most bulls, incomplete evaluations being performed. We need to place more emphasis on bull fertility when selecting herd bulls.
Reproductive efficiency in beef cattle operations continues to be an important economic trait. To help producers optimize reproductive efficiency, bull breeding soundness exams (BBSE’s) are performed prior to the breeding season. This evaluation helps producers detect bulls that are sub-fertile and will have a negative impact on reproductive efficiency. Unfortunately, less than 18% of small cattle producers (< 50 head) and 60% of cattlemen with > 200 head consistency use this tool (NAHMS, 2009). When BBSEs are performed with a high degree of expertise and care nearly 1 in 5 bulls will not pass the exam (Koziol JH, 2018). While BBSEs can be a great tool they also all too often give the producer a false impression that the bull they have purchased or plan to use will perform optimally. The ineffectiveness is due to the way the evaluations are currently performed. Veterinarians collect a semen sample and then evaluate it under a microscope, subjectively estimating the number of progressively motile sperm and then staining a slide, allowing it to dry and checking the sperm for morphological abnormalities. The subjective nature of the evaluation, along with the difficulties to detect acrosome and mitochondrial sheath defects using stained slides and a light microscope creates results that are inconsistent and often unreliable (Perry, 2018). It is not uncommon for veterinarians to feel pressure from bull producers to pass bulls so they can be sold (Barth, 2007). Veterinarians will sometimes completely skip the morphological evaluation (Hopper, 2015) which can account for over 17% of all bulls that are tested to be found unfit for breeding (Thundathil, et al., 2014). In my personal experience as a veterinarian I had never performed a BBSE in veterinary school. During my first job I followed what my new boss did. We looked in the microscope and estimated both motility and morphology using a fresh, undiluted sample. If it wiggled it passed. This method of evaluation, even 20 years later, continues among my colleagues. This form of evaluation is easy, fast, and cheap for the producer, however the costs to the industry are difficult to quantify.
Reproductive efficiency for cow-calf producers has many economic advantages. For this goal, producers need a reliable BBSE test that is consistent and safe from errors commonly encountered today. High reproductive efficiency creates more calves born and calving earlier in the calving season. Earlier calves will weigh more and be will be available for sale earlier. The other important benefit is the ability to produce a more uniform set of calves which is more desirable for buyers who will pay more. The most significant expenses a cow-calf producer has is keeping and maintaining the cow. A cow herd having more calves and heavier calves does not change the input significantly; management and capital input stays relatively constant. Reproductive efficiency, therefore, increases pounds of beef produced while not increasing the use of natural resources or increasing greenhouse gas. Bulls continue to play a significant role in herd reproduction and efficiency. Using high fertile bulls is a must to consistently manage a high reproductively efficient herd (Chenoweth, 2005).
Veterinary bull breeding soundness exams continue to provide the best tool to evaluate bulls for potential fertility prior to bull sales or the breeding season. Veterinarians need a quick and simple method to create an accurate semen evaluation which can be performed chute side. A complete BBSE consists of a physical exam, including evaluation of the internal and external genitalia, scrotal circumference, plus individual sperm progressive motility and sperm morphology. Evaluation of the sperm motility and morphology creates a spermiogram. The Society for Theriogenology (SFT) has set a minimum standard of a least 30% individual forward progressive motility and 70% normal morphological sperm. Morphology is broken down into head, midpiece, and principal piece (tail) (Koziol JH, 2018). A complete differential is not required by the SFT and with over twenty morphological abnormalities this job would be very cumbersome and time consuming. Australia uses a system where all semen samples are submitted to a lab. There, a trained sperm morphologist uses a differential interference contrast (DIC) microscope to evaluate the semen sample. A more complete differential count is completed, and with these specific abnormalities identified, they can determine more precisely when fertility will be adversely affected due to a single abnormality. For example; a detached head does not show any effects on fertility until there are 30-40% found in the sample. In contrast, nuclear vacuoles, one of the more difficult abnormalities to detect, will affect fertility at 15 – 20%. While Australia has a more stringent system to help ensure a quality spermiogram is created, they still have variations between labs and individuals performing the evaluation. The concern of leniency to favor more bulls passing prior to sale is still a potential problem (Perry, 2018). The need for a system where personal biases or conflict of interests are removed, as well as other human imperfections are removed, is necessary to protect the public’s best interest.
A complete spermiogram will help us to better understand the severity of an insult to spermatogenesis, how long ago the effects were initiated, or what type of insult may have caused the abnormalities. This aids in prognosis and future preventative techniques, while also providing us a better idea of when we may want to retest to determine if the bull has recovered. Spermatogenesis is adversely affected due to many environmental and physical factors. These insults include stress, thermoregulation disruption, trauma, seasonal changes, decreases in testosterone levels, fever and/or disease, nutrition, age, genetic, toxins, and others. Using a spermiogram, the physical exam and bull history improves our diagnostic evaluations to better assist bull owners in management decisions (Barth, 2013) (Koziol JH, 2018). A complete accurate differential spermiogram is a must for a quality BBSE and to progress in improving reproductive efficiency.
DIC microscopy is considered the gold standard for semen evaluation; however, this equipment is very expensive and mostly only seen in a laboratory research setting (Chenoweth, 2004). Light microscopes are commonly used today for field evaluation of sperm morphology. These microscopes are relatively inexpensive and can do a fair job. The samples must be prepared using a stain. The most commonly used stain today is eosin nigrosine stains. The stains are applied to create a single mono cell layer and the sample is dried (Koziol JH, 2018). Drying has been shown to change the size of the sperm cells and if dried too fast may cause other artifacts. The technique takes practice to create consistency. Drying has also been shown to cause acrosomal defects. On the other hand, it can be more difficult to detect acrosome defects and nuclear vacuoles using light microscopes in comparison to DIC or phase contrast. Phase contrast allows the user to visualize the semen sample without the need for staining or drying, minimizing the chances for artifacts and improving visibility of the more subtle abnormalities (Freneau GE, 2010). New technologies such as PlasDIC may show some real promise in decreasing the costs and increasing the accuracy of our microscopes. The choice of a microscope is vary important, we can choose cheep and do a fair job or we can invest in very good equipment and do a great job.
Conclusion: We need consistent protocols for performing bull breeding soundness exams. We need to use better evaluation equipment and no longer settle for cheaper equipment. We need to have third party verification for bulls to be sold, this will remove the current conflict of interest that will hamper any human’s judgments. We need to purchase bulls that have a complete third party morphological evaluation performed.
For Producers: When purchasing bulls, don’t allow statements like “fertility guarantee, or all bulls have been fertility checked be enough. Look at the results of breeding soundness exams as closely as you do the bull or any other information that comes with it. Then scrutinize it just as much or more than any other information you receive about that bull.
References
Barth, A. D., 2007. Evaluation of Potential Breeding Soundness of the Bull. In: Large Animal Theriogenology. St. Louis(Missouri): Saunders, pp. 228-243.
Barth, A. D., 2013. Bull Breeding Soundness. 3rd ed. Saskatoon(Saskatchewan): Western Canadian Association of Bovine Practitioners.
Chenoweth, P. J., 2004. Semen Evaluation. North Platte, Proceedings, Applied Reproductive Strategies in Beef Cattle.
Chenoweth, P. J., 2005. Cow/Calf Production Principles. In: Beef Practice: Cow-calf Production Medicine. Ames: Blackwell Publishing, pp. 9-27.
Freneau GE, C. P. E. R. R. G., 2010. Sperm morphology of beef bulls evaluated by two different methods. Animal Reproduction Science, 118(2-4), pp. 176-181.
Hopper, R. M., 2015. Breeding soundness Examination in the Bull: Concepts and Historical Perspective. In: Bovine Reproduction. Oxford: Wiley Blackwell, pp. 58-63.
Koziol JH, A. C., 2018. Society for Theriogenology Manual for Breeding Soundness Examination of Bulls. Second ed. s.l.:Society for Theriogenology.
NAHMS, 2009. Bull management Practices on U.S. Beef Cow-calf Operations, s.l.: APHIS.
Perry, V., 2018. A refrsher on sperm morphology. Brisbane, s.n.
Thundathil, J. C., Dance, A. L. & Kastelic, J. P., 2014. Bovine sperm abnormalities: prevalence, etiology and mechanisms leading to infertility. Clinical Theriogenology, 6(4), pp. 525-532.