Theriogenology Insight - An International Journal of Reproduction in all Animals

Study was conducted to evaluate how heat stress affects follicular size, reproductive hormones, oestrus expression in different seasons. Twelve (n=12) zebu cows were utilized over a year. Ambient temperature, relative humidity was collected and THI value determined, rectal temperatures were also collected. Cows were synchronized for oestrus. Ultrasonic follicular studies were carried out until ovulation. Blood was collected to assayserum concentration of progesterone, oestradiol and Luteinizing hormones using Enzyme -Linked Immunosorbent Assay technique. Oestrus activities were monitored; follicular diameters at 42 hr were shorter P< 0.05 in cold dry season than hot dry and raining season. At 72 hr follicular diameters were longer P< 0.05 in hot dry season than cold dry and raining season. Time to peak of oestradiol was shorter P< 0.05 in cold dry season than hot dry and raining seasons. Amplitude of oestradiol was higher P< 0.05 in cold dry season than hot dry and raining seasons. Time to peak of LH surge was shorter P< 0.05 in cold dry season, than hot dry and raining season. Amplitude of LH surge was higher P< 0.05 in raining season than cold dry and hot dry season. Duration of LH surge was longer P< 0.05 in cold dry season, than hot dry and raining season. Mounting was higher P< 0.05 in cold dry season than raining and hot dry season. Conclusion: Heat stress has increased follicular size without increasing oestradiol concentration, reduced mounting, increased LH surge and progesterone concentration.