Abstract

Study of oestrous cycle of cows is prerequisite for reproductive manipulation aiming optimal genetic gain within existing reproductive and genetic potentialities of the cows. This experiment was carried out based on routine checkup of vaginal electrical resistance (VER), endocrinological assessment of hormonal profiles (progesterone and oestrogen) and ultrasound scanning to observe ovarian follicular dynamics during the course of oestrous cycles of the cross-bred cows. The animals were managed on a uniform field of nutrition, body condition score (BCS) varied from 3.0 to 3.5 (1-5 scale), careful attention was adopted for hygienic approach of experimented animals during reproductive records, instrumental preparation, precautions and application. VER values were registered by electronic oestrus detector (Draminski® Electronic Estrus Detector, Poland), blood was collected, processed to segregate serum by centrifugation (Universal 32R®, Hettich Zentrifugen, Germany), stored at -200C in a refrigerator followed by hormonal evaluation by ELISA test using commercial kits (Nova Tec Immunodiagnostica®, GmbH, Germany), and ultrasound scanning of ovaries to record follicular and luteal data by 7.5 MHz B Mode linear probe (Bionet®, Republic of Korea) daily at the scheduled time of a day. All the data originated during the routine observations of VER, hormonal profiles and ovaries were carefully noted, systematically organized and analysed statistically. The highest and lowest VER values, blood concentrations of progesterone and oestrogen were recorded as 350.56±7.96 and 186.67±12.54 ohms, 1.26±0.01 and 1.04±0.00 ng (nanogram)/ml, 3.09±0.02 and 2.94±0.01 pg (picogram)/ml, respectively. The patterns of VER and progesterone fluctuations were almost equally proportionate but inversely proportional relationship was also observed between VER values and oestrogen profiles. The wave number per cycle and the interovulatory interval (IOI) of the cycles varied from 2 to 3 and 20 to 21 days, respectively on ultrasonographical observations of ovaries of the experimented cows. The variations of VER, progesterone and oestrogen profiles at different stages of the oestrous cycles, and the correlation between VER and hormonal profiles were significantly reflected (P<0.05). Lowest VER values, maximum follicular size and serum concentration of excess oestrogen was indicative for oestrus (follicular phase), and opposite phenomena including hyper concentrations of serum progesterone was exclusively indicative for luteal phase of oestrous cycle.

Keywords

Oestrous cycle, vaginal electrical resistance (VER), hormones, follicular dynamics, cattle