Seasonal influence on the luteal growth and regression characteristics of crossbred dairy cows of Kerala

The study was aimed at investigating the effect of seasonal changes on luteal growth and regression characteristics in crossbred (CB) cows of Kerala. The seasons of the year were classified as rainy (June-September), post-monsoon (October-January) and summer (February- May). In each season, nine healthy regularly cycling CB lactating pluriparous cows were selected for the study. Luteal growth and regression pattern were studied at 24 h intervals from one ovulation to the next ovulation, by transrectal ultrasound (TRUS) examination of the ovaries. During the study period, parameters like the day of earliest detection of corpus hemorrhagicum (CH), size at detection, maximum size of corpus luteum (CL), the day of CL with maximum diameter, day of onset and completion of CL regression were recorded and compared between seasons. Corpus hemorrhagicum was detected one day after ovulation in 55.60, 66.70 and 80 per cent of animals during rainy, post-monsoon and summer seasons, respectively. There existed no statistically significant difference in the size of CL, either on the day of first detection or on the day of maximum size attainment. However, CL during the rainy season needed a significantly (P