Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2000
Publication Date: 6/1/2000
Citation: SASONGKO, B.P., WHITTIER, J.C., BURNS, P.D., GEARY, T.W., MORTIMER, R.G. EVALUATION OF FIXED-TIME AI WITH GNRH ON PREGNANCY RATE OF BEEF HEIFERS SYNCHRONIZED WITH THE MGA/PGF2ALPHA PROTOCOL. JOURNAL OF ANIMAL SCIENCE SUPPLEMENT. 2000. v. 78(Suppl. 2). p. 119. Interpretive Summary:
Technical Abstract: The objective of this study was to evaluate pregnancy rate to timed- insemination with 100 ug of GnRH at 60 h post PGF in beef heifers synchronized with the 14-d MGA/19-d PGF system. The comparison treatment was 14-d MGA/19-d PGF with heat detection and AI up to 72 h, then non- responding heifers were all mated at 72 h. The study was conducted on virgin heifers at two locations in the spring of 1999. In both locations, animals were fed .5 mg MGA/head/d for 14 d. There was a 19-d interval between the end of MGA feeding and the 25 mg injection of PGF. Animals were randomly assigned either to timed AI at 72 h (72) or to 60 h plus 100 ug GnRH injection (60) post prostaglandin injection. Estrous detection began at the same time of PGF injection through 72 h at L2. At L1, estrus was observed starting 1 d before PGF injection through 72 h for animals in treatment 72, but it was from the time of PGF injection to 60 h for 60-treated animals. Animals in treatment 72 that exhibited estrus were bred according to am-pm rule, except for those observed at 72 h and non-responders. All heifers in treatment 60 were bred at 60 h in L1. Animals in treatment 60 that exhibited estrus in L2 were bred according to am/pm rule except for those exhibiting estrus at 36, 60, 72 h and non-responders. There was no interaction between treatments and locations on AI pregnancy rates and thus data were pooled to either 72 or 60 treatment. Chi-square analysis showed similar AI pregnancy rates between treatments. These data indicate that the duration of estrous detection was reduced and similar pregnancy rates were achieved by mating at 60 h with 100 æg GnRH compared to waiting until 72 h post PGF following a 14-d MGA/19-d PGF synchronization system.