Y. Yavas et al., Effectiveness of norgestomet implants in suppressing ovulation and estrus in heifers varies with stage of estrous cycle when implanted, CAN J ANIM, 80(4), 2000, pp. 729-732
Suppression of ovulation and estrus for 63 d by a 24-mg norgestomet ear imp
lant with a delivery rate of 160 mug d(-1) was evaluated in beef heifers. O
vulation was suppressed in 80% of heifers implanted on day 7 of the estrous
cycle, 40% on day 10, 33% on day 13, 53% on day 16, and 67% on day 19 (P <
0.05 for day 7 vs. days 10, 13 and 16). The norgestomet implant was more e
ffective in suppressing ovulation and estrus when inserted on day 7 of the
estrous cycle rather than later in the cycle.