Use of an immunoenzymatic assay to detect the luteinizing hormone peak in bitches.

The success of artificial insemination with fresh chilled or frozen semen depends on the time of insemination. Determination of oestrous behaviour, use of vaginal smears or measurement of the vaginal resistivity are unreliable techniques and interpretation of the dosages of progesterone 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 plasma concentration of LH was measured in ten bitches by a new sandwich immunoenzymatic assay (Reprokit, Sanofi) and results were compared with the vaginal smears and plasma concentrations of progesterone. The LH peak was easily detected and lasted 3.3 days with maximum values ranging from 10 to 22 ng ml-1. At the time of the peak, the vaginal smears displayed features of pro-oestrus and the plasma concentration of progesterone was 2.9 ng ml-1. This immunoenzymatic assay, already used for many species, is an effective tool for determining the time of the LH peak. Added to the study of the progesterone concentration, it may help to determine the optimal time for artificial inseminations, particularly when frozen semen is used.