A long time breeder once told me that donkeys tend to give birth on or near full moon or new moon. Even before this I had read that just as the moon's phase influences tides in the ocean it makes sense that a female's body could be influenced given that 60% of total body weight is water. So does the moon's phase affect our donkeys' birthing dates?
Over the years it seemed to be true but we had no hard data on this. We decided to track our recent births and compare them to the moon phases. We considered 33 births that happened in Stafford, CT at Foster Hill Farm between 2018 and 2020. We stand 3 jacks and have 25 jennets so the dam and sire pairing of each foal was unique in most instances. Of the 33 foals 17 were jacks and 16 were jennets. For all of the time we have been breeding the gender split has been even which is also so fascinating to me.
We took a look at the number of days away from a full or new moon that each foal was born. There are 14 days between a new moon and a full moon with a quarter moon exactly between the 2 at 7 days. 73% of the foals were born 4 days or less from a full or new moon. If the births were evenly distributed among all of the days of the moon's phases there would be 57% of the births within 4 days of the full and new moon combined. So in our small study we did have more births than average closer to the new and full moon phases.
We took this one step further and looked at the number of births that were 4 days or less from the new moon vs. 4 days or less from the full moon. We found that of the 73% of births that occurred 4 days or less from full or new moon, 52% were near the new moon and 21% were close to the full moon. The vast majority of births happened at night however we do not have exact data on that.
Since this has posted we have received feedback that what is really needed is to look at the actual cover date for the jennet and determine if the 12 month due date is influenced in any way by the moon phase. This would be an important next step to determine if perhaps it is the jennets' heat cycle that is influenced by the moon phases and the birth dates are all on on average 12 months from conception. We do hand breed our donkeys initially but then let them run with the jack and record additional breedings and heat cycles that are observed.
There was a study conducted on dairy cattle that showed a correlation between moon phase and birthing patterns. 'There is a popular belief that the lunar cycle influences spontaneous delivery in both humans and cattle. To assess this relationship, we investigated the synodic distribution of spontaneous deliveries in domestic Holstein cows. We used retrospective data from 428 spontaneous, full-term deliveries within a three-year period derived from the calving records of a private farm in Hokkaido, Japan. Spontaneous birth frequency increased uniformly from the new moon to the full moon phase and decreased until the waning crescent phase. There was a statistically significant peak between the waxing gibbous and full moon phases compared with those between the last quarter and the waning crescent. These changes were clearly observed in deliveries among multiparous cows, whereas they were not evident in deliveries among nulliparous cows. These data suggest the utility of dairy cows as models for bio-meteorological studies, and indicate that monitoring lunar phases may facilitate comprehensive understanding of parturition.' (1)
In our small experiment we found the jennets foaling closer to new moon than to full moon like the cattle in the study that is cited above. Whether or not it is the heat cycle that is influenced by the moon or not I found our results interesting once I actually tabulated all of the information. I am not a scientist but am just sharing what we found. We will continue to track this information at Foster Hill Farm. A larger sample could help us to identify birthing timing and patterns for donkeys.
(1) Yonezawa T., Uchida M., Tomioka M., Matsuki N. Lunar Cycle Influences Spontaneous Delivery in Cows. PLoS ONE. 2016;11:e0161735. doi: 10.1371/journal.pone.0161735.[PMC free article] [PubMed] [CrossRef] [Google Scholar]