DETECTION OF THE LH SURGE IN THE COW BY E NZYMOIMMUNOASSAY IN THE LABORATORY OR ON FARM

The aim of the present study was to define the practical conditions to be used for determination of plasma LH concentrations in cows by EIA at the laboratory or on farm. A first investigation compared the LH co ncentrations from plasma sampled every 2 hours from 13 oestrus control led females as determined by RIA and EIA. From these cows, 9 showed an LH surge as observed simultaneously by RIA and EIA. The overall coeff icient of correlation between the concentrations measured by the 2 met hods was 0.80 (p < 0,0001) and varied according to individuals between 0.73 and 0.98. A second trial was designed to evaluate the possible u se of such an EIA on farm. EIA LH determination was then performed fir st on farm and second at the laboratory. Twelve cows were previously o estrus controlled and superovulated. Blood was sampled every 3 hours f or 36 hours. All cows showed an LH surge and this was found both from the on farm and the laboratory assays. Values from these 2 series were highly correlated (r = 0.88; p < 0,0001) but those optical densities determined on farm were slightly but constantly lower (- 10 p. cent) t han those measured at the laboratory. From this study, it was found th at blood sampling every 6 hours was required in order to ascertain the observation of the LH surge. In conclusion, LH EIA on farm can be per formed in order to detect the LH surge of cows prior to insemination a nd possibly adjust the time of AI accordingly. Nevertheless, frequent sampling and carefull use of the test are required.