Temperature regulation of liquid bovine semen can be difficult in field situations. Two experiments were carried out to assess the effect of storage temperature on in vitro sperm characteristics and 60-d nonreturn rate (NRR) following artificial insemination (AI) of liquid bovine semen. In experiment 1, the effect of storage of liquid bovine semen in INRA96 diluent (IMV Technologies, L'Aigle, France) at 1 of 5 storage temperatures (5, 15, or 28°C, and fluctuating between 5 and 15°C or 5 and 28°C) on total and progressive motility and kinematic parameters was assessed objectively via computer-assisted sperm analyzer on d 0, 1, 2, 3, and 4 after collection. Fluctuating temperatures were designed to mimic day- to nighttime variation. In experiment 2, we assessed the field fertility of liquid semen stored at a constant 5 or 15°C or in an unregulated manner and compared with that of frozen-thawed semen (total of n = 106,738 inseminations). In experiment 1, we detected a linear decrease in motility with increased duration of storage. Semen stored at a constant 15°C or fluctuating between 5 and 15°C had greater total motility than semen held at 5 or 28°C or fluctuating between 5 and 28°C; however, semen stored at 15°C and fluctuating between 5 and 15°C did not differ from each other. Semen held at a constant 5 or 15°C or fluctuating between 5 and 15°C, although not differing from each other, had higher progressive motility scores than that held at 28°C or fluctuating between 5 and 28°C. Semen stored at a constant 28°C exhibited poor motility and velocity values but had high progressive motion values compared with that all other storage temperatures; however, the other storage temperatures did not differ from each other in relation to motility kinematics. In experiment 2, semen stored at a constant 5°C resulted in a lower 60-d NRR (62.5%) than storage at constant 15°C or unregulated temperature or frozen-thawed semen (73.6, 74.6, and 74.4%, respectively. In conclusion, sperm stored in IRNA96 are quite tolerant in terms of storage temperature, retaining acceptable motility between 5 and 15°C. Storing semen at a constant 15°C resulted in greater in vitro sperm motility and higher NRR rates than storage at 5°C and did not differ in NRR from frozen-thawed semen or semen stored at an unregulated temperature; however, lower storage temperatures were shown to be more detrimental to sperm in vivo than unregulated storage conditions.
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