Reproductive hormone secretions and first service conception rate subsequent to ovulation control with Synchro-Mate B

Abstract

Two groups of beef females receiving suboptimal energy diets were treated with Synchro-Mate B to control ovulation. The first group consisted of 30 suckled cows and 16 heifers. These females were bled 10 days and immediately prior to the implantation of norgestomet implants, at implant removal, 24, 27, 30, 33 and 36 hours and 9 and 16 days post-implant removal. The second group which consisted of 40 cows and 8 heifers was handled in the same manner except no blood samples were collected from 24 to 36 hours following implant removal. Calves were removed from all the cows for 48 hours, beginning at implant removal. All animals were artifically inseminated 48 hours following implant removal. Blood plasma was assayed for concentrations of progesterone and LH. The first service conception rate was 21% and 40% for groups 1 and 2. Several factors were identified that reduced the first service conception rate. 1. 1) Two of the animals in the first group of females were not synchronized and appeared to ovulate with implants in situ . 2. 2) Heifers not exhibiting ovarian cycles tended to have a lower first service conception rate. Pre-synchronization status (anestrous or cyclic), however, did not affect first service conception rate in the cows. 3. 3) Short luteal phases were detected in 17% of the anestrous cows, and they did not conceive to the timed insemination. 4. 4) First service conception rate was reduced, if the preovulatory LH peak occurred other than at 33 to 36 hours following removal of the implant. 5. 5) Blood samples collected around the time of the LH surge appeared to reduce first service conception rate in both cows and heifers. In summary, Snychro-Mate B is an effective method to synchronize estrus in cattle. However, stress subsequent to implant removal should be avoided in order to obtain a higher first service conception rate.