|Hafs, Harold - RUTGERS UNIVERSITY|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 1998
Publication Date: N/A
Interpretive Summary: Many estrous synchronization programs available to producers have not been documented to be effective in cattle that have not started estrous cycles. We have shown that estrous synchronization using intravaginal progesterone releasing inserts and prostaglandin F2 alpha followed by an injection of estradiol benzoate 24 to 30 h after insert removal increased fertility, even if the cattle had not started estrous cycles at the beginning of treatment. This combined program has the potential to increase the effectiveness of estrous synchronization especially in females without corpus luteum activity, so that artificial insemination and timed insemination can be more easily used in beef cattle.
Technical Abstract: Peripuberal heifers and postpartum cows were used to determine the optimal estradiol benzoate (EB) dose to induce and synchronize estrus after intravaginal progesterone releasing inserts (EAZI-BREED TM insert) treatment. Females received an insert for 7 d (d 0 = insertion day) with a 25 mg injection of prostaglandin F2 alpha on d 6. At 24 to 30 h after insert removal, females were injected with EB: heifers 0, .2, .38, or .75 mg and cows 0, .25, .5, or 1 mg. Starting at EB injection 7 heifers and 7 cows from each dose group were bled every 4 h for 76 h. Samples were assayed for LH and estradiol-17 beta (E2). Estrus was detected twice daily for 21 d after insert removal, and females were artificially inseminated. Pregnancy was determined using ultrasonography. Percentage of females in estrus was greatest (P < .04) at .38 mg in heifers and 1 mg of EB in cows. Dose x time interaction affected (P < .01) E2 in all females. E2 peak had a linear dose increase (P < .03) response only in heifers. Percentage of cows and heifers with LH release was affected by dose with a linear (P < .01) and quadratic (P < .01) response. Peak LH was affected by dose with a linear (P < .01) response in heifers and linear (P < .01) and quadratic (P < .08) in cows. Peak LH also varied (P < .06) with CL activity in cows. Time to LH peak had a linear (P < .03) response in heifers and linear (P < .04) and quadratic (P < .05) in cows. Pregnancy rate was affected (P < .02) in heifers by CL activity and in cows by EB dose (P < .01). In conclusion, a EB injection in females treated with insert and prostaglandin F2 alpha increased E2, LH, and number of animals in estrus. Also, EB increased pregnancy rates in cows. Optimal EB dose was: .38 mg for heifers and 1 mg for cows.