Variables affecting semen quality and its relation to fertility in the dog: A retrospective study

Although semen analysis is routinely used to evaluate the male reproductive potential in the canine species, only a few authors have attempted to relate semen characteristics to donor traits, such as age or weight, and fertility. This study evaluated the effects of dogs' age (young: 0-24 months, adult: 25-84 months, old: >84 months), size (small: <15 kg, medium: 16-40 kg, large: >40 kg) and reason for semen collection (evaluation, artificial insemination, cryopreservation or research purposes) on the seminal characteristics and related the main seminal characteristics with fresh AI results. Overall, 251 semen examinations were performed from 140 dogs presented between 2000 and 2015 at the University of Pisa Veterinary Teaching Hospital. Conventional semen parameters (semen volume, sperm concentration and total number, subjective motility and sperm morphology) were evaluated. Overall, 227 (90.4%) samples contained spermatozoa. Azoospermic samples resulted from complete (n = 13, 9 dogs), or incomplete ejaculations (n = 11, 8 dogs), based on seminal alkaline phosphatase concentration and/or ancillary examinations. Reason for semen collection had a significant effect on semen volume, sperm total number and sperm concentration. The proportion of normal spermatozoa was lower in dogs presented for semen evaluation (P < 0.05). Dog size affected ejaculate volume and total sperm number, which was lower in small dogs compared to medium (P < 0.01 and P < 0.05, respectively) and large-sized dogs (P < 0.01). Age had no influence on volume, sperm number or motility. The proportion of normal spermatozoa was higher in young animals than in old ones (P < 0.05). There was a significantly higher proportion of midpiece defects in old dogs compared to young ones (P < 0.01). Total sperm number, motility and proportion of morphologically normal spermatozoa in the semen used in AIs resulting in a pregnancy were 627.6 × 10⁶, 83.9% and 64.9%, respectively, all significantly higher than in the unsuccessful AIs, where they were 389.4 × 10⁶, 66.5% and 42% (P < 0.05). In conclusion, age, size and reason for semen collection may affect main sperm parameters and must be taken into consideration during the interpretation of a routine semen evaluation. In turn, altered semen parameters may affect fertility after artificial insemination.