Induction of follicular wave emergence for estrus synchronization and artificial insemination in heifers

The objective was to synchronize follicular wave emergence among cattle for synchronization of estrus and ovulation, and to determine pregnancy rate a fter AI at observed estrus. At random stages of the estrous cycle, a contro lled internal drug release device (CIDR-B) was inserted intravaginally (Day 0) in 67 cross-bred beef heifers, and they were randomly allocated to rece ive either no further treatment (Control; n = 18); 5 mg of estradiol-17 bet a and 100 mg of progesterone im (E/P; n = 16); 100 mug im of GnRH (GnRH; n = 16); or transvaginal ultrasound-guided follicular ablation of all follicl es greater than or equal to5 mm (FA; n = 17). All heifers received a luteol ytic dose of PGF (repeated 12 h later), and CIDR-B were removed on Days 9, 8, 6 or 5, in Control, E/P, GnRH or FA groups, respectively, so the dominan t follicle of the induced wave was exposed to exogenous progesterone for a similar period of time in each group. Mean (+/- SEM) intervals land range, in days) from treatment to follicular wave emergence in these groups were 3 .5 +/- 0.6 (-2 to 8), 3.4 +/- 0.1 (3 to 4), 1.5 +/- 0.3 (-1 to 4), and 1.0 +/- 0.1 (0 to 2), respectively. Although the interval was longest (P<0.01) in the E/P and Control groups, it was least variable (P<0.01) in the E/P an d FA groups. Intervals land range, in days) from CIDR-B removal land first PGF treatment) to estrus were 2.3 +/- 0.2 (1.5 to 4.5), 2.2 +/- 0.2 (1.5 to 3.0), 2.1 +/- 0.1 (1.5 to 3.5), and 2.5 +/- 0.1 (2.0 to 3,5), and to ovula tion were 3.5 +/- 0.2 (2.5 to 5.5), 3.4 +/- 0.1 (3.0 to 4.5), 3.5 +/- 0.1 ( 2.5 to 4.5), and 3.8 +/- 0.1 (3.0 to 4.5), for Control, E/P, GnRH and FA gr oups, respectively (ns). The proportion of heifers displaying estrus was hi gher in the Control than in the FA group (94% versus 65%, P<0.05) and inter mediate in EP and GnRH groups (87% and 75%). Heifers were inseminated appro ximately 12 h prior to ovulation (based on estrous behavior and ultrasound examinations). Pregnancy rates were 78%, 80%, 69% and 65% for Control, E/P, GnRH and FA groups, respectively (P=0.73). Results support the hypothesis that synchronous follicular wave emergence results in synchronous follicle development and, following progesterone removal, synchronous estrus and ovu lation with high pregnancy rates to AI. The synchrony of estrus and ovulati on in the E/P, GnRH and FA groups suggest that these treatments, in combina tion with CIDR-B, could be adapted to fixed-time insemination programs. (C) 2000 by Elsevier Science Inc.