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Abstract This study compared reproductive outcomes among two protocols for synchronization of ovulation that provide for a lengthened proestrus with the conventional oestradiol‐based protocol currently used for timed‐AI (TAI). Holstein heifers (13–15 months) at one location were assigned randomly to one of three TAI protocols. Heifers ( n = 150) in the 7‐day oestradiol benzoate (EB) group received a progesterone device (Cue‐Mate) and 2 mg EB on Day 0; 500 μg of cloprostenol (PGF) and Cue‐Mate removal on Day 7; 1 mg of EB on Day 8 and TAI on Day 9 (54 h after Cue‐Mate removal). Heifers ( n = 150) in the 5‐day CO‐Synch (CO) group received a Cue‐Mate and 100 μg of gonadotropin‐releasing hormone (GnRH) on Day 2; Cue‐Mate removal and PGF (twice, 12 h apart) on Day 7; and GnRH along with TAI on Day 10 (72 h after Cue‐Mate removal). Heifers ( n = 150) in the J‐Synch (JS) group received a Cue‐Mate and 2 mg of EB on Day 1; PGF and Cue‐Mate removal on Day 7; GnRH and TAI on Day 10 (72 h after Cue‐Mate removal). Heifers were inseminated by one technician with frozen–thawed conventional semen from one of four commercially available sires. Plasma progesterone (P4) concentrations (ng/mL) were determined at Cue‐Mate removal and TAI. Ovarian ultrasonography was done in a subset of 217 heifers at the initiation of protocols, at Cue‐Mate removal; TAI; and 7 days after TAI. Approximately, 28 and 50 days after TAI pregnancy status was determined by ultrasonography. Mean (±SEM) plasma P4 concentration at Cue‐Mate removal was greater ( p < .01) in CO (6.02 ± 0.2) and JS (6.51 ± 0.2) compared to EB heifers (4.53 ± 0.2). Mean (±SEM) plasma P4 concentration at TAI was lowest in the JS (0.28 ± 0.05), intermediate in CO (0.46 ± 0.02), and greatest in EB heifers (0.66 ± 0.05, p < .01). The diameter of the ovulatory follicle (mean ± SEM) was the smallest in the JS group compared to that in the CO and EB groups (15.8 ± 0.5; 13.9 ± 0.5; and 12.7 ± 0.5 mm for EB, CO and JS, respectively). More ( p < .01) heifers in the JS group had their oestrous cycle synchronized (50.0, 78.8 and 82.4% for EB, CO and JS groups), and were pregnant at 28 (40.3, 51.3 and 63.3% for EB, CO and JS groups) and 50 days after TAI (32.6, 46.0 and 60.0% for EB, CO and JS groups). In summary, heifers subjected to the J‐Synch TAI protocol had lower P4 at TAI, and better overall response to hormonal treatments, which resulted in increased P/AI at 28 and 50 days after TAI compared to those heifers subjected to either a 7‐day EB protocol or a 5‐day CO‐synch protocol.
Dirandeh et al. (Thu,) studied this question.