Natural influence of season on follicular, luteal, and endocrinological turnover in Indian crossbred cows

Abstract

The study was aimed at investigating the effect of seasonal changes on follicular and luteal dynamics in vivo in normally cycling crossbred cows during summer and winter months of the year. Six healthy regularly cycling Jersey crossbred nonlactating pluriparous cows were used for the study. Follicular and luteal developmental pattern was studied every other day throughout the estrous cycle by scanning the ovaries during two periods of a year viz., hot season (April to June; n = 16) and cold season (December to February; n = 12). Plasma progesterone (P4) concentrations were measured on Days 0 (estrus), 6, and 12 of the estrous cycle. Among the 12 cycles studied during the cold season, 11 (91.7%) had three waves and one had two waves. Of 16 cycles studied during the hot season, eight (50%) had two waves, four (25%) had three waves, and the remaining four cycles had single (n = 2) and four waves (n = 2). High P4 concentrations during the midcycle would have suppressed the dominant follicle of the second follicular wave and induced the emergence of the third wave during the cold season. The first follicular wave (wave I) of the cycle emerged much earlier (Day 0.5 ± 0.3) during the cold season than that in the hot season (Day 1.7 ± 0.4). The ovulatory wave emerged significantly earlier during the hot season (Day 11.5 ± 1.3) than in the cold season (Day 14.8 ± 0.4), and hence, the growth phase of ovulatory follicle significantly increased during the former season (11.0 ± 1.4 days) than the latter (5.8 ± 0.2 days). The ovulatory follicle attained a significantly larger diameter (12.8 ± 0.8 mm) to express the estrus during the hot season when compared to the cold season (11.3 ± 0.4 mm), which might be indicative of alterations in steroidogenic activity within the follicular microenvironment. During the midphase of the cycle, a period critical for embryonic sustenance, the P4 level was significantly reduced in the hot months indicating suppression of luteal activity during hot period of the year. Thus, it could be concluded that increased incidence of two follicular waves associated with a prolonged growth phase of the ovulatory follicle, and altered luteal endocrine activity during the hot season might be associated with decreased fertility in crossbred cattle.