Gonadotrophin-releasing hormone treatment in cattle: a meta-analysis of the effects on conception at the time of insemination
1993
Morgan, W.F. | Lean, I.J. (Sydney Univ. (Australia). Dept. of Animal Science)
Data from 40 trials described in 27 published papers were analysed by meta-analysis (pooling of data from numerous trials into a single analysis) involving a total of 19 019 cows. Mantel-Haenszel analysis revealed that use of GnRH at insemination significantly increased the overall risk of pregnancy by 12.5 percent in treated cows. However, increases in risk of pregnancy were greatest (22.5 percent) when repeat breeders were treated. Results for use of GnRH or analogue at first service were similar, with increased risks of pregnancy in treated cows of 5.2 and 8.0 percent, respectively. The risk of pregnancy tended to be higher (11.1 percent) when the dose of GnRH was 250 microg or more and when used at second insemination (9.9 percent). The analysis demonstrated that while treatment at insemination with GnRH and GnRH analogues increased conception rates in dairy cattle, some variation in study results was attributable to the number of inseminations after calving at which GnRH is administered.
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