Effect of season and genotype on values for bull semen variables under tropical conditions

• Published in: Animal reproduction science Vol. 221; p. 106592
• Main Authors: Landaeta-Hernández, Antonio J., Gil-Araujo, Marcelo A., Ungerfeld, Rodolfo, Owen Rae, D., Urdaneta-Moyer, Angela, Parra-Núñez, Alexander, Kaske, Martin, Bollwein, Heinrich, Chenoweth, Peter J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2020
• Subjects: Andrology; Bulls; Environment; Semen; Stress; Tropics; Bulls; Andrology; Environment; Semen; Stress; Tropics
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2020.106592

•Seasonal period and bull genotype are important factors affecting fresh semen traits in the tropics.•Even under improved management conditions, the elevated THI of this tropical zone negatively influenced sperm output.•Bos indicus and crossbred taurus x indicus were the least affected by seasonal variations.•Improved results should occur by using tropically adapted genotype bulls for breeding purposes. 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.