Abstract
To assess the effects of season and genotype on fresh semen quality for freezing and subsequent use for AI, 32 healthy, mature (>4 to <6 years old) and habituated bulls (Bos indicus n = 14, Bos taurus n = 5, Crossbred taurus x indicus n = 6, and tropically adapted Bos taurus composites n = 7) were evaluated at a Venezuelan AI center for 12 months in which four distinct seasons (Hot-dry, Transition, Hot-humid, Cool-rainy) occur. Ejaculates were collected weekly from Bos taurus (n = 260), Bos indicus (n = 669), tropically adapted Bos taurus composites (n = 389), and crossbred Bos taurus x Bos indicus (n = 340) bulls. Routine AI Center assessments were conducted i.e., ejaculate volume (EV), sperm mass-motility (MM), total sperm number/ejaculate (TSE), sperm concentration/mL (SC), pre-freezing (PREF), and post-freezing minimum criteria rate for AI use (POSTF). Genotype affected EV (P < 0.0001), TSE (P < 0.0001), and SC (P < 0.0001) but not MM (P>0.05). Season affected EV (P < 0.001), TSE (P < 0.0001), SC (P < 0.01), and MM (P < 0.05). There were genotype x season interactions for EV, MM, TSE, and SC. The PREF averaged 74.0% during the study, although was less (P < 0.0001) during the hot-humid season than the other seasons. Even though, percent ejaculates considered unsuitable for freezing differed (P < 0.03) among the Hot-dry (20.2%), transition (30.9%), Hot-humid (32.4%), and Cool-rainy (24%) seasons. For POSTF, there were no seasonal differences (P>0.05). It is concluded that in tropical regions, season and genotype can affect bull semen variables, particularly those which affect the success of semen freezing and AI.
Landaeta-Hernández, Antonio J