Synchronizing follicular waves using 14 day CIDR insert protocols in beef cows and assessing reticulo-rumen temperature changes for detection of ovulation in dairy cows

Abstract

In the first experiment, objectives were to determine the effectiveness of an extended controlled internal drug release (CIDR) insert estrus synchronization protocol to produce 2 follicular waves, induce cyclicity in anestrus cows, and evaluate the efficacy of a single 50 mg dose of prostaglandin F2α (PG) at CIDR removal. This experiment included 779 primiparous and multiparous lactating beef cows at 3 locations (n = 779) that were randomly assigned to 1 of 3 treatments. Cows in the 14-d 50 PG treatment received a CIDR (1.38 g progesterone) with 100 μg GnRH analogue im on d 0, 100 μg GnRH analogue im on d 9, and CIDR removal with 50 mg PG im on d 14. Cows in the 14-d 6 h PG treatment were assigned the same protocol as the 14-d 50 PG treatment except that 25 mg PG im was given on d 14, plus 25 mg PG im 6 ± 1 h later. Cows in the 5-day CO-Synch + CIDR (5-d CO-Synch) treatment, received a CIDR with 100 μg GnRH analogue im on d 9, CIDR removal with 25 mg PG im on d 14, and 25 mg PG im 6 ± 1 h after first PG injection. Cows in all treatments received 100 μg GnRH analogue im with TAI 72 ± 3 h after CIDR removal. Pregnancy status to TAI was determined by ultrasonography 37 to 40 d after TAI. Pregnancy rate to TAI was higher (P < 0.05) in 14-d 50 PG treatment than 14-d 6 h PG and 5-d CO-Synch treatments. In the following year, 2 experiments were conducted at 6 locations. Our objectives were to: 1) determine the efficacy of an extended CIDR protocol with 2 induced follicular waves, and 2) determine the ability of initiating the CIDR protocol with GnRH analogue (Factrel) or PG. In exp. one, 588 primiparous and multiparous lactating beef cows at 2 locations were randomly assigned to 1 of 3 treatments. Cows in the 14-d GnRH-9 treatment (n = 202) received the same treatment as the 14-d 50 PG as described earlier. Cows in the 14-d GnRH-7 treatment received a CIDR insert and 100 μg GnRH analogue im on d 0, 100 μg GnRH analogue im on d 7, and CIDR removal with 25 mg PG im on d 14. Cows in the 7-day CO-Synch + CIDR (7-d CO-Synch) treatment, received a CIDR insert and 100 μg GnRH analogue im on d 7, and CIDR removal concurrent with 25 mg PG im on d 14. Cows in all treatments received 100 μg GnRH analogue im with TAI at either 72 ± 3 h (14-d GnRH-9 treatment) or 63 ± 3 h (14-d GnRH-7 and 7-d CO-Synch treatments). Combined across all locations, pregnancy rates to TAI were not different (P > 0.05) between 14-d GnRH-9 (54.8%), 14-d GnRH-7 (54.4%), and 7-d CO-Synch (52.3%) treatments. In exp. two, 625 primiparous and multiparous lactating beef cows across 4 locations were randomly assigned to 1 of 3 treatments. Cows in the 14-d GnRH treatment (n = 205) received the same treatment as the 14-d 50 PG treatment described earlier. Cows in the 14-d PG treatment (n = 214) received the same treatment as 14-d GnRH cows except that 25 mg PG im was given on d 0 instead of GnRH analogue. Cows in the 5-day CO-Synch treatment (n = 206), received the same treatment as described previously. Cows in all treatments received 100 μg GnRH analogue im with TAI 72 ± 3 h after CIDR removal. Combined across all locations, pregnancy rates to TAI were higher (P < 0.05) in the 14-d PG treatment (70.4%) than both the 14-d GnRH (54.4%) and 5-d CO-Synch (53.5%) treatments. The final experiment assessed changes in reticulo-rumen temperature to detect ovulation in lactating dairy cows. Lactating dairy cows (n = 494) ≥ 46 days in milk at 1 location were enrolled in a standard presynchronization protocol which included 2 PG injections 14 d apart. Twelve d later, cows were enrolled in an ovulation synchronization protocol of 100 μg GnRH im (d -10), 500 μg cloprostenol im (d -3), and 100 μg GnRH im 48 h later. All cows received TAI 16 to 19 h after the second GnRH injection. Blood was collected throughout the synchronization period to determine cycling status, response to synchronization treatments, and ovulation around the time of TAI. Reticulo-rumen temperature (Trr) was recorded by temperature recording reticulo-rumen boluses administered to each cow via balling gun within 24 h of calving. Each Trr reading was recorded every time animals entered the milking parlor to establish a 7 d baseline. The single maximum Trr rise (°C) from baseline on d of TAI (TrrMAX) and the average of all (1 to 3) Trr readings on d of TAI (TrrAVG) were used for analysis of Trr change related to ovulation. Mean (± SE) TrrMAX rise from the baseline tended to be higher (P = 0.06) in ovulatory (n = 446; 0.180 ± 0.023°C) than anovulatory (n = 48; 0.094 ± 0.042°C) cows. Mean (± SE) TrrAVG was higher (P < 0.01) in ovulatory (0.064 ± 0.011°C) than anovulatory (-0.047 ± 0.046°C) cows. The use of changes in Trr in ovulatory cows has been validated to pinpoint animals that do in fact ovulate in an estrus synchronization protocol.