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Puppy Litters Conceived Under a Full Moon Contain More Males

The phases of the moon can influence the sex distribution of puppies

Key points

  • There are many examples indicating that the phase of the moon is associated with changes in physiology and behavior.
  • In the same way that the moon affects ocean tides, phases of the moon affect hormonal releases in animals.
  • Litters of puppies conceived under the full moon have a higher percentage of males than those conceived under the new moon.
By kxp130 and licensed under CC BY-NC 2.0
Source: By kxp130 and licensed under CC BY-NC 2.0

There are many superstitions about the effect that the moon has on life and behavior. Every fan of horror movies knows that traditionally werewolves appear only in the light of the full moon. In Shakespeare’s “Othello,” the maid Emilia tells Othello that the moon has drawn too close to the Earth and driven men insane. In fact, the "luna" in the word "lunacy" refers to the moon. One clearly observable effect of the moon is the rising and falling of the ocean's tides.

Considering the fact that most higher animals, including humans, are made up of 70 percent water, it makes some sense that the moon could have an impact on our physiology and psychology. Furthermore, if we can believe some new research coming out of Italy, the lunar cycle also has an influence on dogs, and may well predict the relative number of male and female puppies in a litter.

There are four prominent phases of the lunar month: new (no moon visible), waxing (the moon is gradually growing brighter as the lighted area increases), full (the visible moon is completely illuminated), and waning (the amount of illuminated area is decreasing). According to the position of the moon in its orbit, during the various phases, the gravitational pull of the moon on Earth changes, as does the amount of cosmic electromagnetic radiation that hits the Earth's surface. There have been numerous scientific studies that show that the lunar cycle has an impact on human beings.

The effects indicate a lunar influence on human reproduction, including fertility menstruation and birth rate. Admittance to the hospitals and emergency units due to various causes such as cardiovascular and acute coronary events have also been shown to be correlated with the moon's phases. It has been suggested that the gravitational and electromagnetic variations during the lunar cycle cause these effects by triggering the release of neurohormones, specifically melatonin and endogenous steroids.

Not too long ago, in 2005, a modest-sized investigation looked at some women in Nepal. The study monitored the timing of their ovulation and then determined which women got pregnant during the full moon and compared them to a group of women who got pregnant during the darker phases of the moon. They found that the women who got pregnant during the full moon were more likely to give birth to male babies than those who conceived their children during the darker phases of the moon. Just recently a team of Italian researchers, headed by Daniela Alberghina of the Department of Veterinary Science at the University of Messina, used that finding as a starting point and asked the question as to whether the lunar cycle might also predict the proportion of male and female puppies in litters.

These investigators looked at 150 litters of Labrador Retrievers (a total of 973 offspring). They considered the day of conception to be 62 to 64 days before the day the litter was delivered. They then divided the month into the traditional four phases going from waxing moon, through new moon, then waning moon, and finally full moon. Their results were similar to the findings in the study of Nepalese women. These investigators found that there were statistically more male puppies in litters conceived during the full moon, as compared to litters conceived during the new moon, as can be seen below.

SC Psychological Enterprises Ltd. based on data from Alberghina et al, (2021).
Effect of Phases of the Moon on the Percentage of Male Puppies in a Litter
Source: SC Psychological Enterprises Ltd. based on data from Alberghina et al, (2021).

These results indicate a really strong effect of the lunar cycle on the distribution of sexes in the litters. For litters conceived under the full moon, there were 62 percent male puppies; however, that number was reduced to only 41 percent for litters conceived during the new moon. There was an approximately 20 percent difference in the number of male puppies caused by the effect of the phases of the moon.

When I read these results I thought of an incident from my childhood. My Aunt Sylvia had two children, both daughters, and she and her husband dearly wanted to have a son to round off their family. I remember my Lithuanian grandmother (who was a reservoir of folk wisdom and superstition) wagging her finger at Sylvia and advising, "If you want a boy you must make love during the light of the full moon." These results certainly provide similar advice to dog breeders. If you want more male dogs in your litters, mate your dogs during the full moon. If you want more female dogs choose the new moon for your pairings. I don't know whether my Aunt Sylvia took my grandmother's advice, but her next child was a boy.

Copyright SC Psychological Enterprises Ltd.


Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission

Daniela Alberghina, Mauro Gioè, Marco Quartuccio & Luigi Liotta (2021): The influence of lunar cycle at the time of conception on sex offspring distribution in dogs, Chronobiology International, DOI: 10.1080/07420528.2021.1933001

Sarkar M, & Biswas NM. (2005). Influence of moonlight on the birth of male and female babies. Nepal Medical College Journal, 7(1): 62-4.