The study was conducted to evaluate the effect of heat stress on follicular size, oestradiol concentrations and oestrus expression in different seasons on Zebu cows. Twelve (n=12) matured, Zebu cows were utilized for over a year. The year was divided into 3 phases. Ambient temperature, relative humidity and rectal temperature were determined using. Cows were synchronized for oestrus. Ultrasonic follicular studies were carried out daily. Blood samples were collected after administration of a second dose of PFG2α to assess serum concentration of oestradiol. The enzyme-linked immunosorbent assay technique was used to determine the concentration of oestradiol. Oestrus activities were monitored by visual observation. Follicle diameters at 24 hr were lower (P< 0.05) in the cold, dry season (6.34± 0.68 mm) than hot dry (8.09±0.52 mm) and the rainy season (8.62±0.9 mm). At 72 hr, follicular diameters were significantly higher P
Key words: Follicle, Estradiol, Heat stress, Season, Zebu cow
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