Chapter 6 Richard M. Hopper Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, Mississippi, USA Evaluation for breeding soundness of the bull provides information that is vital for the cowman and in turn the beef cattle industry. In fact information from the National Animal Health Monitoring System (NAHMS) reports on utilization of various management practices by cattlemen reveals that the bull breeding soundness examination (BBSE) is a valued and much-utilized procedure. At each category of operation based on herd size, the percentage of cattlemen who utilized a BBSE was equal to or greater than those that utilized palpation for pregnancy and several other veterinary services.1 Additionally, numerous studies reveal the advantage to cattlemen of this management tool, when either a herd fertility standard as measured through pregnancy rate or an economic value is used to compare BBSE-evaluated and -passed bulls versus general population bulls.2 A correctly performed BBSE provides an assessment of a bull’s breeding potential but only for the date performed. For a bull to successfully breed cows in a pasture environment he must be able to survive (maintain body condition), identify females in estrus, and deliver fertile semen into their reproductive tract. Thus a BBSE should include thorough physical, reproductive tract, and semen examinations. The evolution of the BBSE that is currently in use is a testimony to the foresight and persistence of a group of veterinarians (both practitioners and academicians) and animal scientists who identified a problem, specifically subfertility in bulls, and worked to continually improve the metrics that could be used to validate the fertility or subfertility of a bull. While it is true that very few bulls are in fact completely sterile, the incidence of subfertility can be 20–40% in groups of bulls.3 Thus the goal of a BBSE is to identify subfertile bulls so that they may be removed from the breeding population. Therefore major emphasis must be placed on physical attributes that affect a bull’s ability to breed cows and metrics of semen production and quality. Over the years, increased understanding of the factors possessed by a bull that impact overall herd fertility, as measured by both pregnancy rate and percentages of cows impregnated at each time period within the calving season, has led to increased emphasis on measurement of scrotal circumference (SC) and microscopic evaluation of sperm morphology. SC, specifically in bulls under the age of 4 years, is highly correlated to sperm production. Evaluation of sperm morphology is likely the single most important criterion to be evaluated with respect to identifying fertile versus subfertile bulls. Historically, the need to identify sterile or marginally fertile bulls in North America came to a point of importance in the winter of 1949 after a brutal snowstorm that occurred throughout the northern section of the mid-western and Rocky Mountain states of the United States. Many bulls suffered severe frostbite of the scrotum and so their subsequent fertility was an obvious concern. In response veterinarians initiated attempts at evaluating the semen of these bulls. Semen samples were obtained by manual deviation of the penis into an artificial vagina as the bull mounted a restrained cow.4 While this is commonly performed at bull studs, the practice did not lend itself to range cattle, so this was both labor-intensive and dangerous to the operator. Once a semen sample was obtained, a microscopic examination of motility was performed. While this event and the ensuing activity viewed through the lens of our current standards for evaluation of bull fertility might seem crude, this was indeed the impetus for the development of the electroejaculator, the early organization (Rocky Mountain Society for the Study of Breeding Soundness) that subsequently became today’s Society for Theriogenology (SFT), the professional organization that sets the standards for breeding soundness examinations for all domestic species of both genders, an American Veterinary Medical Association approved specialty, the American College of Theriogenologists (ACT), and likely much of the literally thousands of publications resulting from the last 60 years of research in bovine fertility. So, finally, to answer the question: What is a BBSE? Basically stated, a BBSE must identify whether or not a bull so examined “is able to produce adequate numbers of normal spermatozoa and possess the ability and desire to deposit these sperm into a cow.”5 This statement, made by Dr J.N. Wiltbank at the Annual Meeting of the SFT in 1982, continues to adequately describe the mission of a BBSE. The standards for the BBSE that are currently in use were adapted in 1992 by a select committee of the SFT and in fact the form developed and utilized is under copyright by that organization. This form has been effectively constructed to include all of the components of a BBSE in an organized format and on a single page (Figure 6.1). A useful aspect of the format is that a veterinarian new to the procedure or an infrequent user can easily utilize the form as a template, ensuring that all aspects of the examination are completed. Figure 6.1 Bull Breeding Soundness Evaluation form. Society for Theriogenology, 1992. Used with permission. A previous evaluation system followed the premise that once the physical attributes of a bull had been examined and found satisfactory, the rest of the examination (SC, sperm motility, and sperm morphology) could be evaluated with a scoring system. Thus the SC would be measured and a score applied, as well as an individual score for motility and one for morphology. A bull’s “score” was a total of the three individual scores. It was soon determined that this system was flawed in that a very good score in one area could help a bull pass, even when he might have a substandard score in another area. The current system is an improvement in that a bull must meet minimum standards in each area in order to be classified “satisfactory.” Additionally, there is evidence that the current standards put in place in 1992 are more stringent and have resulted in fewer marginal bulls passing.6–8 Another aspect of this evaluation system is the acknowledgment that the fertility of some bulls, typically young peripubertal bulls, as well as bulls that have experienced a transient illness resulting in a raised body temperature or a bull that has been exposed to extremes in environmental temperature (high or low) or to stress, will improve over time, once the inciting cause has been removed. If in the opinion of the veterinarian performing the BBSE, a bull does not currently meet standards but is likely to improve, the bull can be classified as “deferred.” This bull should then be retested at a later date, typically 60 days later, but often earlier based on the judgment of the veterinarian performing the examination. A bull that for any reason does not meet the standards of the BBSE and is unlikely to meet them at a later date is classified “unsatisfactory.” Thus the BBSE begins with a history, which in fact may be a herd history. A general physical examination, followed by an examination of the urogenital system, and measurement of the SC all precede the collection of semen. Microscopic examination of sperm motility and morphology follow. Because of the importance of this procedure, separate chapters of this book have been devoted specifically to the physical and urogenital examination and the collection and evaluation of semen (Chapters 7 and 8). Additional chapters cover the use of the electronic BBSE (Chapter 83), a recently developed software program that allows information derived from the BBSE to be captured and stored digitally, and the enhanced diagnostic evaluation of semen (Chapter 74).
Breeding Soundness Examination in the Bull: Concepts and Historical Perspective
Introduction
What is a BBSE?
Overview of the current BBSE
Limitations and concerns
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