Effects of dietary energy on sexual maturation and sperm production in Holstein bulls.

In prepubertal bulls and heifers of dairy and beef breeds, puberty can be induced to occur earlier than typical with targeted high-energy diets due to precocious activation of the endocrine mechanisms that regulate puberty. Precocious activation of puberty in bulls intended for use in the AI industry has the potential to hasten and perhaps increase sperm production. It was hypothesized that feeding bulls a high-energy diet beginning at 8 wk of age would advance the prepubertal rise in LH and lead to advanced testicular maturation and age at puberty.

Comparison of follicular dynamics and hormone concentrations between the 7-day and 5-day CO-Synch + CIDR program in primiparous beef cows.

The objectives were to compare follicular dynamics, preovulatory estradiol concentrations, and progesterone concentrations between the 7-day (7CO, n = 15) and 5-day (5CO, n = 13) CO-Synch + controlled internal drug release device (CIDR) program in primiparous suckled beef cows. On Day -7 (7CO) or Day -5 (5CO), GnRH (100 μg) was administered (GnRH-1) and a CIDR was inserted. On Day 0, hour 0, CIDR was removed and cows received PGF2α (25 mg) at hours 0 and 12.

Decreasing the interval between GnRH and PGF2alpha from 7 to 5 days and lengthening proestrus increases timed-AI pregnancy rates in beef cows.

Four experiments were conducted in postpartum beef cows to evaluate the influence of reducing the interval from GnRH to PGF(2alpha) from 7 to 5d in a Select-Synch + CIDR or CO-Synch + CIDR estrous synchronization program. In Expt 1, cows (n=156) were treated with either a 7 or 5d Select-Synch + CIDR program. A second PGF(2alpha) treatment was given to all cows in all experiments at 12h after the initial PGF(2alpha) (to ensure that luteolysis occurred with the 5d program).