Pheromones for modulating reproduction in cattle: biological potential of oestrus-related substances inintra- and inter-species chemical communication

Declining dairy cow fertility, largely attributable to increasing milk yields, is of major concern to dairy farmers worldwide. New tools for reproductive management, to replace exogenous hormones, would be of great interest. Chemical communication in cattle has been suggested to cause modifications of the oestrous cycle. Here, reproductive parameters were monitored in ten dairy heifers during five oestrous cycles. They were exposed to distilled water (control) or oestrous urine and vaginal mucus (treatment). Four of them were also subjected to intensive blood sampling to study the treatment effect on the LH pulsatility pattern (LHP) preceding the preovulatory LH surge (LHS).We found that the treatment had significant effects on when the different signs of oestrus occurred and on the intensity of oestrus expression. There was a tendency for treatment to have an effect on LHS characteristics whereas LHP was significantly affected by the treatment. To find a quick bioassay to detect bioactive bovine body fluids, two heifers and two bulls were exposed to different body fluids while their heart rates were registered. Although the exposure caused significant effects, they were not of sufficient magnitude to be useful. Further attempts to find a bioassay to identify oestrus-specific compounds included using the face fly as a biological detector. Female flies were allowed to choose between either oestrous (OU) or luteal urine (LU) and distilled water (control) in a Y-tube olfactometer. Flies were significantly repelled by OU, but not by LU. Gas chromatography coupled with electroantennographic detection (GC-EAD) revealed no behaviourally active, oestrusspecific compounds. Comparison of chromatograms, however, showed that cetyl alcohol was more abundant in OU than in LU. When tested at different doses, the lowest dose of cetyl alcohol was found to attract flies, while the second lowest dose was repellent. We found effects of exposure to body fluids on cyclicity in heifers, as well as on heart rate in cattle, which supports the existence of bovine pheromones. We also found that the face fly could discriminate between OU and LU, probably based on the amount of cetyl alcohol in the samples. Neither monitoring of heart rate, nor using the face fly as a biological detector, were suitable bioassays for detection of bovine pheromones.