PHOTOPERIOD AND SEASONAL INFERTILITY IN THE PIG AND THE POTENTIAL OF EXOGENOUS MELATONIN AS A PREVENTIVE: A REVIEW E.B. GREER* SUMMARY

and not high ambient temperature, appears to be the major cause of seasonal infertility in pigs. Attempts to counter depressed fertility during summer by cooling sows are often unsuccessful. In contrast, artificially reducing daylength during summer shortened the wean-to-oestrus interval of a commercial sow herd by 18d to 5.7d. A similar programme also improved boar fertility. However, there are likely to be practical difficulties in manipulating daylength in the normal Australian style of housing for breeding pigs. It is suggested that parenteral or oral administration of the "daylength " hormone, melatonin, may have potential as a counter to seasonal infertility. (Keywords: sows, infertility, temperature, photoperiod, melatonin