Pregnancy rate among beef heifers from timed insemination following synchronization with a progestin treatment.

Five trials were conducted with 958 virgin beef heifers to evaluate the effects of various breeding management methods on pregnancy rate at synchronized estrus and during a 45-day artificial insemination (AI) season. Synchronization was achieved with the progestin treatment regimen Syncro-Mate-B (SMB). Pregnancy rate at first service and cumulative pregnancy rate were affected (P less than .01) by trial. Pregnancy rate at first service was 55% for all heifers on the SMB treatment regimen and 67% for nontreated control heifers (P less than .01). However, cumulative pregnancy rate during the 5-day synchronized period was higher (P less than .01) among treated heifers (54%) than among control heifers (21%). The pregnancy rate was 6% higher (P less than .06) after 27 days of breeding for treated heifers than for control heifers. Neither pregnancy rate at 21 days nor final pregnancy rate after a 45-day AI season was significantly affected by treatment. Pregnancy rate at first service among heifers undergoing the SMB treatment regimen and inseminated 12 hr after first detected in estrus was not significantly different from that among heifers inseminated once from 45 to 55 hr after implant removal or heifers inseminated twice at 48 and 60 hr after implant removal, regardless of occurrence of estrus.