Effect of season of the year and phase of the moon on puberty and on the occurrence of oestrus and conception in dairy heifers reared on high planes of nutrition

A study of the factors that influence the age at first oestrus has been made with 57 Friesian heifers reared on high planes of nutrition in a partially-controlled environment. Although animals born during the period of increasing daylength reached puberty approximately 2 months earlier than those born during decreasing daylength, there was also a marked influence of live weight at 182 days of age and of the phase of the moon at the time of oestrus. Frequency of occurrence of first oestrus and of conception showed four distinct peaks at approximately 7-day intervals within the lunar cycle; this association between conception and lunar phase appeared to decline with increasing parity. Frequency of occurrence of artificial insemination, which reflected all suspected instances of oestrus, was also related to lunar phase. This effect of the lunar phase appears to be associated in the young heifer with 7-day cycles of oestrous activity positioned in time by the occurrence of the full moon.