Factors affecting sperm abnormalities and breeding soundness classification of bulls kept on commercial farms in Zambia

A total of 441 eosin-nigrosin bull breeding soundness examination (BBSE) data was obtained from Matobo Veterinary centre and analysed. 82 bulls were classified as unsound for breeding representing 18.6% of the entire bull population studied. The breeds studied were the Bonsmara, Sussex, Brahman, Boran, Afrikander × Tuli and the Tuli. Breed and scrotal circumference (SC) were the significant predictors of BBSE classification. The Bonsmara and the Sussex breeds were not significantly different in predicting sperm abnormalities (p>0.05). The Brahman breed had odds of 0.358 less likely to be classified as sound, Boran breed had odds of 0.206 less likely to be classified as sound and the Afrikander × Tuli breed had odds of 0.097 less likely to be classified as sound while the Tuli breed had odds of 0.214 less likely to be classified as sound. Therefore, the Afrikander × Tuli breed had the highest probability of being classified as unsound for breeding. Bulls with a SC of <36 cm had odds of 0.235 less likely to be classified as sound while those of 39 to <42cm had odds of 0.384 less likely to be classified as sound compared to bulls with SC of ≥42cm. Body condition score (BCS) had an effect on mass motility (p<0.05). Bulls in month category (cat) 1 (September, October and November) had odds of 2.29 more likely to have fair mass motility relative to very good mass motility compared to bulls examined in June-July (cat 2) and month category 1 bulls had odds of 2.46 more likely to have good mass motility relative to very good mass motility compared to month category 2 bulls. Bulls in SC category 1 (≤39 centimetres (cm)) had odds of 1.81 more likely to have fair mass motility relative to very good mass motility compared to bulls in category 2 (>39cm) and bulls in BCS category 1 (2.5 and 3.0) had odds of 2.71 more likely to have fair mass motility relative to very good mass motility compared to bulls in category 3 (4.0). Bulls with a BCS of 4.0 had the highest mass motility of 3.72±0.41 and the lowest was recorded in Bulls of BCS 2.5, 2.39±0.24 (p<0.05). The month of November had the lowest mass motility of 2.26±0.15 (p<0.05) and bulls of age <36 months had the lowest mass motility of 3.08±0.14 while the highest was recorded in bulls of age 48 to <60 months 3.73±0.08 (p<0.05). Bulls with a SC of ≥42 cm had the highest mass motility of 3.85±0.06 and the lowest was seen in bulls of SC <36 cm, 2.83±0.14 (p<0.05). The Sussex breed had the highest mass motility of 3.97±0.09 and the lowest was seen in the Afrikander × Tuli breed 1.69±0.39 (p<0.05). The month of November had the highest percent total abnormalities of 20.73±2.56% and July with the lowest of 8.98±0.66% (p<0.05), The Afrikander × Tuli breed had the highest total abnormalities of 25.50±6.62% while the Bonsmara breed had the lowest of 7.24±0.43% (p<0.05). Bull of age <36 months had the highest total abnormalities of 17.19±2.02% and the lowest in bulls of age range 48 to <60 8.23±0.72% (p<0.05). Bulls with SC <36cm had the highest total abnormalities of 19.00±1.82% while those of ≥42 cm had the lowest 7.63±0.72% (p<0.05). The highest total abnormalities was recorded in those bulls with a BCS of 4.0 as 24.67±11.47% and the lowest in bulls of BCS 3.5, 9.15±0.54% (p<0.05). In conclusion, Breed and SC had an effect on sperm abnormalities, BBSE classification and mass motility. Body condition score, age and month had an effect on mass motility and total sperm abnormalities. This therefore signifies why morphological sperm determinations are important in predicting bull fertility.