RESUMEN
This study evaluated the use of cooled semen in a fixed-time artificial insemination (FTAI) program compared with frozen-thawed semen to improve pregnancy rates in beef cattle. Ejaculates of three bulls were collected and divided into two treatments: (1) frozen-thawed semen and (2) cooled semen. Egg-yolk extender without glycerol was used for the cooled semen treatment. Straws (25×106 spermatozoa) were submitted to cooling for preservation at 5°C for 24h, after which FTAI was performed. Nelore cows (n=838) submitted to FTAI were randomly inseminated using frozen-thawed semen or cooled semen. There was a 20% increase in the pregnancy per AI (P AI-1) using cooled semen compared with frozen-thawed semen (59.9±4.7 vs 49.4±5.0%; P<0.005). There was no difference in P AI-1 among the bulls (P=0.40). The frozen-thawed semen had fewer functional spermatozoa than did the cooled semen when evaluated by sperm motility (61.7 vs 81.0%), slow thermoresistance test (41.7 vs 66.7%) and hypoosmotic swelling test (38.3 vs 53.7%; P<0.05). The percentage of sperm abnormalities did not differ between the freeze-thawing and cooling processes (18.6 vs 22.1%; P>0.05). Because there was less damage to spermatozoa and improvement in P AI-1, the use of cooled semen instead of frozen-thawed semen is an interesting approach to increase reproductive efficiency in cattle submitted to a FTAI protocol.
