title: Evaluation of two progestogen-based estrous synchronization protocols in yearling heifers of Bos indicus × Bos taurus breeding.
abstract: Yearling Bos indicus × Bos taurus heifers (n = 410) from three locations, were synchronized with either the Select Synch/CIDR+timed-AI (SSC+TAI) or 7-11+timed-AI (7-11+TAI) treatments. On Day 0 of the experiment, within each location, heifers were equally distributed to treatments by reproductive tract score (RTS; Scale 1-5: 1 = immature, 5 = estrous cycling) and body condition score. The 7-11+TAI treatment consisted of melengestrol acetate (0.5 mg/head/d) from Days 0 to 7, with PGF(2α) (25 mg im) on Day 7, GnRH (100 μg im) on Day 11, and PGF(2α) (25 mg im) on Day 18. The SSC+TAI heifers received the same carrier supplement (without MGA) from Days 0 to 7, and on Day 11 they were given 100 μg GnRH and an intravaginal CIDR (containing 1.38 g progesterone). The CIDR were removed on Day 18, concurrent with 25 mg PGF(2α) im For both treatments, estrus was visually detected for 1 h twice daily (0700 and 1600 h) for 72 h after PGF(2α), with AI done 6 to 12 h after a detected estrus. Non-responders were timed-AI and received GnRH (100 μg im) 72 to 76 h post PGF(2α). The 7-11+TAI heifers had a greater (P < 0.05) estrous response (55.2 vs 41.9%), conception rate (47.0 vs 31.3%), and synchronized pregnancy rate (33.5 vs 24.8%) compared to SSC+TAI heifers, respectively. Heifers exhibiting estrus at 60 h (61.7%) had a greater (P < 0.05) conception rate compared to heifers that exhibited estrus at ≤ 36 (35.3%), 48 (31.6%), and 72 h (36.2%), which were similar (P > 0.05) to each other. As RTS increased from ≤ 2 to ≥ 3, estrous response, conception rate, synchronized pregnancy rate, and 30 d pregnancy rate all increased (P < 0.05), irrespective of synchronization treatment. In conclusion, the 7-11+TAI treatment yielded greater synchronized pregnancy rates compared to SSC+TAI treatment in yearling Bos indicus × Bos taurus heifers.
authors.affiliation: Department of Animal Sciences, The University of Florida, Gainesville, FL 32611, USA.
authors.forename: E N
authors.initials: EN
authors.lastname: McKinniss
authors.forename: R D
authors.initials: RD
authors.lastname: Esterman
authors.forename: S A
authors.initials: SA
authors.lastname: Woodall
authors.forename: B R
authors.initials: BR
authors.lastname: Austin
authors.forename: M J
authors.initials: MJ
authors.lastname: Hersom
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.forename: J V
authors.initials: JV
authors.lastname: Yelich
mesh_terms: D000818:Animals; D001947:Breeding / Q000379:methods*; D002417:Cattle; D004973:Estrus Synchronization / Q000187:drug effects / Q000379:methods*; D005260:Female; D005306:Fertilization; D007315:Insemination, Artificial / Q000662:veterinary; D011247:Pregnancy; D018873:Pregnancy Rate; D011372:Progestins / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*
chemical_list: D011372:Progestins