have on the outcome of the BBSE can be attributed to whether the information is used for a direct assessment of whether the bull is ready to join the breeding herd on a given date or whether the information is being used to leverage fertility selection pressure. In this context, a direct measurement regardless of age, weight, or breed would provide useful information on whether a bull is mature and suitable to be introduced into the breeding herd on a given date. In contrast, if information is to be used to generate accurate selection data, variably referred to as estimated breeding valuations (EBVs) or expected progeny differences (EPDs), then interpretation based on weight, age, and breed become important.
These variations on how the SC information can be used leads to the need to be clear on the purpose for which the BBSE is being performed. The argument could be made that the primary purpose of the BBSE is to determine if an individual bull is suitable for purpose on a specific date. In this instance, a one‐off SC measurement close to the time of entering the breeding herd may be suitable. Conversely, the question is raised of whether it is the role of the veterinarian to fail a bull that is producing semen of acceptable quality if the SC measurement, often taken without important context such as accurate age, breed, weight, and body condition score information, doesn't meet the threshold.
Bull‐Side Semen Evaluation
All standards recommend the collection of semen as part of the routine BBSE. However, not all standards explicitly state semen evaluation as a compulsory element of the examination. The ACV standards provide for the option of no semen evaluation, but mandate the compulsory reporting on their certificates of whether semen assessment is included in the evaluation.
For most regions, there was the option for assessment of gross motility (mass activity), apparently based on tradition. But in regions where standards were accompanied by a manual, practitioners were cautioned against using this parameter as part of the BBSE. Notably, the SFT no longer recommends the use of gross motility as part of the semen assessment process and has now removed it from the BBSE form.
All regions recommend assessing individual motility as a compulsory aspect of the BBSE. In regions where manuals are available there is clear recognition that individual motility is readily affected by artifact. To counteract this, detailed procedural guidelines are provided including the requirement for clean, warmed contact surfaces, the use of a binocular microscope, and the recommendation to dilute the semen to ensure the activity of individual cells can be readily assessed. Two of the four regions recommending semen dilution prior to motility assessment provide explicit guidelines for this dilution process, where semen is recommended to be diluted to turbid consistency (between 60 and 200 million/ml) with warmed phosphate buffered saline to ensure repeatable estimates [16, 23]. In the Netherlands, the recommendation is for a 1 : 80 dilution of semen to diluent, providing sperm concentrations of less than 20 × 106 for assessment.
Variation exists in the interpretation of the individual motility assessment. The South African system has the toughest standard, requiring individual motility to be greater than 70%. The ACV, BCVA, and WCABP systems don't consider that the bull meets the requirements for this standard unless it is greater than 60% motile. But the ACV system also accepts that although semen quality may not be suitable for freezing, bulls used solely for natural mating can have commercially acceptable fertility if the motility is greater than 30%. The ACV system therefore allows a “qualified” rating for this standard for individual motility scores between 30 and 60%. The SFT lower threshold for individual motility has been 30% since the first iteration of its BBSE system in the 1970s. This figure recognizes the need to confirm there are motile spermatozoa, but also recognizes that assessments are made in varied field conditions that can adversely affect motility.
Laboratory Assessment of Semen
Semen Morphology
The standards from all regions recommend collection of semen and the assessment of sperm morphology when performing a BBSE. The South African, BCVA, and SFT standards explicitly state that bulls must exceed the morphology threshold of 70% normal spermatozoa to pass the examination and receive the respective certification. The ACV risk‐assessment model explicitly provides for the option of no morphological evaluation but mandates the compulsory reporting on their certificates of whether morphology is included in the assessment. In this latter standard, options are provided for separating the semen evaluation into “bull‐side” assessment (see section “General Concepts”) and morphological assessment. If morphological assessment is performed in the ACV system, a count of 70% normal is required to meet the category requirements, but a “Qualified” assessment can be assigned to this category for bulls with normal sperm percentages between 50 and 69%, which is justified based on industry‐specific research [25].
All regions other than the ACV recommended morphology be assessed with either a nigrosin‐eosin stained slide or with a preserved, fixed sample under phase‐contrast or differential interference contrast (DIC) microscopy. The ACV does not provide the option of nigrosin‐eosin stained slides for morphology, instead recommending that bull‐side samples be preserved in warmed fixative, such as formal buffered saline, or phosphate‐buffered saline (PBS) glutaraldehyde for subsequent assessment.
There are definitive recommendations for the morphological classification of sperm in the SFT, ACV, and BCVA systems. In these systems sperm abnormalities are recorded as seen. There is no clear recommendation regarding morphology classification in the South African system, but the inference is a focus on assessing the number of normal spermatozoa, with abnormalities individually recorded. The conclusion is that morphology assessment for all regions has moved away from previous classification systems such as primary/secondary or major/minor abnormalities. There is still reference to the compensable/uncompensable classification method in the SFT and ACV manuals, with suggestion it may be suited to assessing sperm morphology in samples that will be inseminated, but not relevant to the BBSE process [10, 23].
One specific morphological defect that is the subject of varied opinion is that of distal cytoplasmic droplets (DDs). The SFT no longer considers DDs as having an adverse effect on fertility and counts them as normal (technically a variation of normal) in the spermiogram. The ACV had previously recommended counting DDs as normal sperm, but currently they are recorded as abnormal sperm. The ACV recommends that if the percentage of DDs is great enough to influence whether a bull meets the morphology standard, then the percentage of DDs, accompanied by an interpretation, should be clearly noted in the comments section for this category so that vendors and purchasers can make an informed decision.
The range of regulatory control over morphology assessment processes and efforts to standardize the procedure varies considerably between regions. The South African and BCVA systems simply state that morphology be performed as part of the evaluation, relying on veterinary undergraduate training and personal continuing professional development (CPD) to maintain integrity of the process and interpretation. The SFT provides a detailed manual on sperm morphology assessment and details current knowledge of the influence of morphology on bull fertility to assist practitioners with their interpretations. The ACV system also provides a manual with detailed morphological assessment and interpretative information. But uniquely, while any veterinarian may perform their own morphology assessments, the ACV strongly recommends samples be sent to an ACV endorsed andrology/morphology laboratory to ensure all bulls are assessed by a standard procedure under high‐quality optics. The inference from the ACV recommendation is that current Australian undergraduate veterinary training and the quality of microscope optics in the clinical setting may not adequately equip veterinarians for performing repeatable and reproducible morphological evaluations that will stand up to commercial scrutiny. While this position is not necessarily relatable to other regions, it does raise the question of whether the assessment, recording, and reporting of sperm morphology should be subjected to quality assurance practices that are followed for many other laboratory processes. The commercial implication of aberrations in morphology assessment or interpretation is that the
