Study of the effect of milk production level and parity on early postpartum ovarian follicular function in dairy cow

The aim of the present study was to evaluate the effect of milk production level and parity on early postpartum ovarian follicular function in dairy cows. Nineteen Holstein lactating cows were assigned based on their milk production into two high (≥35 kg/d) and low-producing (<35 kg/d) groups. Weekly ovarian follicular studying was performed using ultrasound، starting at 7 days after calving continuing for five weeks. Number and size of follicles were recorded. The bloods were collected weekly at the same time of ovarian monitoring to determine blood metabolites and estradiol hormones. Results showed no significant relation between the levels of milk production with follicle size. Mean (±standard error) of follicle size for high and low-producing cows were 9. 06±0. 90 and 11. 13±0. 58 mm throughout experimental period، respectively. Mean (±standard error) of follicles size did not differ between monoparous and multiparous cows. Blood plasma concentrations of estrogen and progesterone were greater in low and high-producing cows، respectively. Least squares means of blood glucose، total cholesterol، HDL-C and LDL-C did not differ significantly during the experiment and between low- and high-producing cows. In conclusion، this study indicated that the size of preovulatory follicles were the same in low and high-producing cows and also between monoparous and multiparous cows. Therefore، milk production and parity can not reduce postpartum reproductive performance through influencing follicle size.