“Previous research from our laboratory in beef cattle suggests that ovarian follicle maturity and subsequent fertility is influenced by length of proestrus across a range of follicle sizes. To test this hypothesis an animal model was used in which ovulation from similar sized follicles was induced following
either a long (LPE; similar to 2.25 days) or short (SPE; similar to 1.25 days) proestrus (interval from PGF(2 alpha) administration to a GnRH-induced LY3039478 inhibitor LH surge). Specific objectives were to compare pregnancy rates and luteal phase concentrations of progesterone (Experiment I) and to characterize preovulatory concentrations of estradiol, the GnRH-induced LH surge, and concentrations of progesterone in the subsequent estrous cycle (Experiment 2) between the LPE and www.selleckchem.com/products/btsa1.html SPE treatments. In Experiment 1, ovulation from follicles that were previously synchronized using follicular aspiration was induced with GnRH (Day 0) after either 2.25 days (LPE; n = 40) or 1.25 days (SPE; n = 38) of proestrus. Lactating and non-lactating cows were inseminated 12 h following GnRH administration. Ovulatory follicle diameter was similar between treatments. Pregnancy rates to AI were
greater (P < 0.01) in the LPE (50.0%) compared to the SPE (2.6%) treatment. The proportion of cows having a short luteal phase in the subsequent estrous cycle was greater (P < 0.01) in the SPE than LPE treatment. In cows with a luteal phase of normal length, timed-AI pregnancy rates and concentrations of progesterone in the subsequent luteal phase were greater (P < 0.05) in the LPE than SPE treatment. In Experiment 2, a similar experimental approach was taken with non-lactating beef cows and ovulation was induced following either 2.2 days (LPE; n = or 1.2 days (SPE; n = of proestrus. Ovulatory follicle diameter was similar between
treatments. Concentrations of estradiol during the proestrus period were CRT0066101 solubility dmso greater (P < 0.05) in the LPE than SPE treatment from Days -1.9 to Day 0 (GnRH administration). Concentration of LH during the GnRH-induced LH surge and concentrations of progesterone in the subsequent estrous cycle did not differ between treatments although there was a tendency (P = 0.10) for increased incidence of short luteal phases in the SPE treatment. In conclusion, decreasing the length of proestrus before induction of ovulation of a large follicle resulted in lesser pregnancy rates and an increased incidence of short luteal phases. The impact of a shortened proestrus on concentrations of progesterone in cows with luteal phases of normal length varied among experiments.