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1 Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
2 Department of Animal Sciences, University of Missouri, Columbia 65211
Corresponding author: J. S. Stevenson; e-mail: jss{at}ksu.edu.
Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48 h after PGF2
, with timed AI [TAI] 12 to 20 h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF2-induced luteolysis. Four treatments were: 1) 100 µg of GnRH at 48 h after PGF2 (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1 mg of ECP for GnRH, and injecting ECP at 24 h after PGF2 (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24 h after PGF2 and was monitored every 6 h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1 ± 0.7 vs. 12.2 ± 0.9 h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26 ± 2 vs. 30 ± 3 h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.
Key Words: estrogens • progesterone • GnRH • ovulation
Abbreviation key: CIDR = controlled internal drug-releasing intravaginal insert containing progesterone, CL = corpus luteum, ECP = estradiol cypionate, Heatsynch = injection of GnRH 7 d before an injection of PGF2, followed in 24 h by 1 mg of ECP and one fixed-time AI 42 to 50 h after ECP, Heatsynch + CIDR = same as Heatsynch plus a CIDR insert for 7 d at the time of first GnRH injection, Ovsynch = injection of GnRH 7 d before and 48 h after an injection of PGF2, with one timed AI at 16 to 22 h after the second GnRH injection, Ovsynch + CIDR = same as Ovsynch plus a CIDR insert for 7 d at the time of first GnRH injection, P4 = progesterone, TAI = timed AI.
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  J. S. Stevenson, M. A. Portaluppi, and D. E. Tenhouse Ovarian Traits After Gonadotropin-Releasing Hormone-Induced Ovulation and Subsequent Delay of Induced Luteolysis in an Ovsynch Protocol J Dairy Sci, March 1, 2007; 90(3): 1281 - 1288. [Abstract] [Full Text] [PDF]
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P. Melendez, G. Gonzalez, E. Aguilar, O. Loera, C. Risco, and L. F. Archbald Comparison of Two Estrus-Synchronization Protocols and Timed Artificial Insemination in Dairy Cattle J Dairy Sci, December 1, 2006; 89(12): 4567 - 4572. [Abstract] [Full Text] [PDF]
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J. S. Stevenson and S. M. Tiffany Resynchronizing Estrus and Ovulation After Not-Pregnant Diagnosis and Various Ovarian States Including Cysts J Dairy Sci, November 1, 2004; 87(11): 3658 - 3664. [Abstract] [Full Text] [PDF]
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S. Z. El-Zarkouny and J. S. Stevenson Resynchronizing Estrus with Progesterone or Progesterone Plus Estrogen in Cows of Unknown Pregnancy Status J Dairy Sci, October 1, 2004; 87(10): 3306 - 3321. [Abstract] [Full Text] [PDF]
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