USE OF AN IMMUNOENZYMATIC ASSAY TO DETECT THE LUTEINIZING-HORMONE PEAK IN BITCHES

The success of artificial insemination with fresh chilled or frozen se men depends on the time of insemination. Determination of oestrous beh aviour, use of vaginal smears or measurement of the vaginal resistivit y are unreliable techniques and interpretation of the dosages of proge sterone may be critical as it may vary from one laboratory to another. The plasma concentration of LH displays a peak of secretion that can be a good reference to date the events of the ovarian cycle. The plasm a concentration of LH was measured in ten bitches by a new sandwich im munoenzymatic assay (Reprokit (R), Sanofi) and results were compared w ith the vaginal. smears and plasma concentrations of progesterone. The LH peak was easily detected and lasted 3.3 days with maximum values r anging from 10 to 22 ng ml(-1). At the time of the peak, the vaginal s mears displayed features of pro-oestrus and the plasma concentration o f progesterone was 2.9 ng ml(-1). This immunoenzymatic assay, already used for many species, is an effective tool for determining the time o f the LH peak. Added to the study of the progesterone concentration, i t may help to determine the optimal time for artificial inseminations, particularly when frozen semen is used.