The oestrous cycle of the cow: Hormonal parameters and time relationships concerning oestrus, ovulation, and electrical resistance of the vaginal mucus

A synopsis is presented of hormonal profiles (peripheral plasma values of LH, FSH, progesterone; urinary estrogens) during the estrous cycle of cattle. After ovulation (day one) progesterone levels begin to increase from about day 4, reach a plateau around day 10, and decrease to basal concentrations starting on days 17 to 18. Corresponding with the progesterone decrease, urinary estrogens show a main increase reaching its maximum one day before ovulation. LH levels are fairly constant from ovulation until day 5, small but significant peaks can be observed between days 6 and 10 in some cows (6 out of 21) and levels then decrease from day 11 to 13. A gradual additional increase begins on day 17, resulting in the preovulatory LH peak 25.7±6.9 h (n=75) before ovulation. This peak has a duration of 7.4±2.6 h (n=89) and occurs any time of the day but preferentially around 8 a.m. and 8 p.m. respectively. Likewise related are the two main periods for ovulation. During estrus, (average duration of 16.9±4.9 h (n=28)) the electrical resistance of the vaginal mucus decreases and the lowest values always correspond with the LH-peak. FSH levels show a wavelike pattern with peaks around days 4, 8, 12-13, 17, 18 and also coinciding with the pre-ovulatory LH peak. The sharp decrease in FSH between the two peaks on day 17 and 18 correlates with the decrease of progesterone during luteolysis. Obviously there is a parallelism between FSH elevations and follicular growth (determined by means of pelviscopic observations).