Effect of treatment with progesterone and oestradiol when starting treatment with an intravaginal progesterone releasing insert on ovarian follicular development and hormonal concentrations in Holstein cows

Ovarian follicular development and concentrations of gonadotrophin and steroid hormones were studied in non-lactating Holstein cows following administration of progesterone (P4) or oestradiol benzoate (ODB) at the start of treatment with an intravaginal progesterone releasing insert (IVP4) in a 2 by 2 factorial experiment. Cows were treated at random stages of the oestrous cycle with an IVP4 device (Day 0) and either no other treatment (n=8), 200 mg of P4 IM (n=9), 2.0 mg of ODB IM (n=8) or both P4 and ODB (n=9). Seven days later devices were removed and PGF2α was administered. Twenty-four hours later 1.0 mg of ODB was administered IM. Oestrus was detected in 97.1% and ovulation in 64.7% (effect of treatment, P=0.41) of cows within 96 h of removing inserts. In the cows that ovulated, day of emergence of the ovulatory follicle was delayed (P<0.01) and more precise (P<0.05) in cows treated with ODB compared to the cows treated with P4. Interval from wave emergence to ovulation and the diameter of the ovulatory follicle was less (P<0.05) in cows treated with ODB compared to cows treated with P4. Combined treatment with P4 and ODB at the time of starting treatment with an IVP4 device did not significantly change the pattern of ovarian follicular development compared to treatment with ODB alone. Concentrations of LH and FSH in plasma were less in cows treated with ODB between Days 0 and 4 (P<0.05) while treatment with P4 increased concentrations of FSH in plasma between Days 0 and 4 (P<0.05). When anovulatory cows were compared to ovulatory cows, diameters of follicles (P<0.001) and growth rate of follicles (P<0.01) were less in anovulatory cows between Days 7 and 9, while concentrations of FSH in plasma were greater (P<0.01), concentrations of LH similar (P>0.90) and concentrations of oestradiol were less (P=0.01) in the anovulatory cows between Days 4 and 10. ndings support a hypothesis that ovarian follicular development following administration of P4 or ODB at the start of treatment with an IVP4 device differs. Anovulatory oestrus may have been associated with reduced maturity and/or later emergence of ovarian follicles.