ABSTRACT
The objective of this study was to compare the fertility of Holstein heifers under cooling and inseminated with sexed semen during the summer versus winter season. Eighty heifers were divided into two groups: (1) summer group (n = 40), consisted of heifers under visual heat detection and inseminated with sexed semen. These heifers were also provided with artificial cooling under shade area from 1000 to 1800 h. (2) Winter group (n = 40), heifers under shade only and with the same reproductive protocol than the summer group. The rectal temperature and respiratory rate were higher (P < 0.05) in the summer group. Vaginal temperature presented higher values in summer (P < 0.05) in most of the daylight hours except between 1100 and 1200 h (P > 0.05). Progesterone, as measured from the AI to 21 days after AI, showed higher values (P < 0.05) in days 6, 12, 18, and 21 during summer compared with winter in pregnant heifers; also, non-pregnant heifers had higher concentrations of progesterone on days 6, 9, 15, and 21 (P < 0.05) in winter. The conception rate in winter at day 35 post-AI (65%) was higher (P < 0.05) than those observed during summer (37.5%). In conclusion, although the lower fertility observed during summer with sexed semen, it can be considered as normal and comparable to the conception rate with conventional semen under hot climate.
