INVESTIGATION BY METAANALYSIS OF THE EFFECT OF PROSTAGLANDIN-F2-ALPHAADMINISTERED POST-PARTUM ON THE REPRODUCTIVE-PERFORMANCE OF DAIRY-CATTLE

The effects of injecting prostaglandin F-2 alpha (PGF) in dairy cattle within 40 days of calving on the rate of pregnancy at first service a nd on the number of days open were investigated by meta-analysis, by p ooling data from numerous independent trials into single analyses. A t otal of 4052 cows from 24 trials described in 10 papers were included in the analyses of first service pregnancy rate and 2646 cows from 21 trials described in nine papers in the analyses of the number of days open. The analyses were stratified by trial and by the reproductive he alth of the cows after calving. Treatment with PGF during this early p ost partum period had no significant effect on the first service pregn ancy rate of cows with a normal or abnormal puerperium. An analysis of the data for the number of days open by effect-size methods showed th at a significant percentage (54 per cent) of the treated cows had fewe r days open than the untreated cows, and that this difference tended t o be greater for cows with an abnormal puerperium (59 per cent of trea ted cows). The weighted average reduction in days open between the tre ated and control cows was 2.6 days for trials with abnormal cows, and 3.3 days for trials including normal and abnormal cows. However, the c alculation of the fail-safe number (F) indicated that it would require only a few studies with a negative response to PGF to negate this fin ding. Meta-analysis was a useful technique for evaluating the apparent ly conflicting results of previous studies.