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1 Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
In Experiment 1, 308 Holstein cows were assigned randomly to four treatments: 1) GnRH injection followed in 7 d by PGF2
injection, then another GnRH injection 33 h later, and artificial insemination (AI) 16 to 18 h after the second GnRH injection; 2) GnRH injection followed in 7 d by PGF2 injection and AI only after detected estrus; 3) injections of PGF2 14 d apart, GnRH injection 33 h after the second PGF2 injection, and AI 16 to 18 h later; and 4) injections of PGF2 14 d apart, AI only after detected estrus following the second PGF2 injection or, in the absence of detected estrus, at 80 h after the second PGF2 injection. In Experiment 2, 227 Holstein cows were assigned randomly to two treatments: 1) GnRH injection followed in 7 d by PGF2 injection, then another GnRH injection 48 h later, and AI 16 to 18 h after the second GnRH injection; and 2) GnRH injection followed in 7 d by PGF2 injection and AI only after detected estrus. Although conception rates in both experiments resulting from AI made after detected estrus either tended to be greater or were consistently greater than those following GnRH injection and one fixed-time AI, pregnancy rates were of greater magnitude after fixed-time AI because of poor expression or detection of estrus.
Key Words: OvSynch • synchronized estrus • pregnancy • rates
Submitted on June 12, 1998
Accepted on November 20, 1998
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