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Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
Corresponding author: J. S. Stevenson; e-mail: jss{at}ksu.edu.
We compared outcomes of 2 protocols used to resynchronize estrus and ovulation in dairy females after a not-pregnant diagnosis. Nulliparous heifers and lactating cows in which artificial insemination (AI) occurred 41 ± 1 d earlier were presented every 2 to 3 wk for pregnancy diagnosis by using ultrasonography. Ovaries were scanned, follicles were mapped and sized, presence of corpus luteum was noted, and GnRH was injected (d 0). Females were assigned randomly to receive PGF2
7 d later (d 7) and then either received estradiol cypionate (ECP) 24 h after PGF2 (d 8; Heatsynch; n = 230) or a second GnRH injection 48 h after PGF2 (d 9; Ovsynch; n = 224). Those detected in estrus since their not-pregnant diagnosis were inseminated, whereas the remainder received a timed AI (TAI) between 65 and 74 h after PGF2. Ovarian scans and blood collected before injections for progesterone analysis were used to classify 4 ovarian status groups: anestrus, follicular cysts, luteal cysts, and cycling, plus an unknown group of females in which no blood sampling or ovarian scans were made. Few females (5.1%) were inseminated between not-pregnant diagnosis and d 8. On d 10, more ECP- than GnRH-treated females were inseminated after detected estrus (24 vs. 6%). Overall, more Ovsynch than Heatsynch females received a TAI (82 vs. 62%). Conception rates tended to be greater for females inseminated after estrus (37%) than after TAI (29%), particularly for those treated with Heatsynch (41 vs. 27%) than with Ovsynch (33 vs. 31%). Those inseminated after estrus conceived 31 ± 8 d sooner than those receiving the TAI. Conception rates for females having elevated progesterone 7 d after the not-pregnant diagnosis were greater than those having low progesterone in Heatsynch (42%; n = 133 vs. 25%; n = 55) and Ovsynch protocols (33%; n = 142 vs. 15%; n = 45), respectively. Conception rates were greater in nulliparous heifers than in lactating cows (43 vs. 28%) regardless of protocol used. Although overall pregnancy outcomes after a not-pregnant diagnosis were similar in response to either the Ovsynch and Heatsynch protocols, inseminations performed after detected estrus before the scheduled TAI reduced days to eventual conception and tended to increase conception rates, particularly after Heatsynch.
Key Words: synchronized estrus • ovulation • cysts
Abbreviation key: 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, Ovsynch = injection of GnRH 7 d before and 48 h after an injection of PGF2, with one fixed-time AI at 16 to 22 h after the second GnRH injection, P4 = progesterone, TAI = timed AI
This article has been cited by other articles:
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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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R. A. Sterry, M. L. Welle, and P. M. Fricke Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows. J Dairy Sci, June 1, 2006; 89(6): 2099 - 2109. [Abstract] [Full Text] [PDF]
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J. S. Stevenson and A. P. Phatak Inseminations at Estrus Induced by Presynchronization Before Application of Synchronized Estrus and Ovulation J Dairy Sci, January 1, 2005; 88(1): 399 - 405. [Abstract] [Full Text] [PDF]
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