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Is Pregnancy Length in Martina Franca Jennies Influenced by Lunar Cycle?

In humans and animals there is a popular belief that spontaneous parturition, and therefore pregnancy length, could be influenced by the lunar cycle, but results from humans are often impaired by multiple variables of the studied population. In domestic animals those problems can be limited by studying restricted population, such as a single breed, reared under uniform conditions. The present study aimed to assess the possible influence of the lunar cycle on pregnancy length in Martina Franca jennies belonging to a single breeding farm. The retrospective study was performed on data collected from 96 Martina Franca healthy jennies with a normal singleton pregnancy course. The present study showed that, whit lunar cycle divided in 4 lunar phases, neither lunar phase at ovulation, nor lunar phase at foaling significantly influenced pregnancy length (371.8±6.45 days). Pregnancy length was not significantly influenced also by the month of the year in which ovulation and spontaneous foaling occurred, as well as by jennies’ age and foal’s sex. In conclusion, pregnancy length in Martina Franca jennies is very variable (335-395 days) but does not Arch Vet Sci Med 2021; 4 (2):34-42 DOI: 10.26502/avsm.023 Archives of Veterinary Science and Medicine 35 seem to be influenced by lunar phases at ovulation or at foaling, month of ovulation and foaling, and by jennies’ age and foal’s sex. Further studies are needed to clarify the reasons for this pregnancy length variability in Martina Franca donkey breed.


Introduction
In humans and animals many different physiological aspects were reported to be influenced by the moon phase [1]. In human's, it is often perceived that the onset of delivery can be influenced by environmental factors. Some climatic parameters, such as the atmospheric pressure, the time of the day, and day within the week, are reported to influence the admission to the hospital for labor and/or delivery [2][3][4]. Beside the above-mentioned climatic factors, also the lunar phases are supposed to influence the time of delivery, even if the scientific studies results remain controversial [4][5][6][7][8][9][10][11][12][13][14]. The main concern regards multiple variables of the studied population according to genetics, social, nutritional, and environmental conditions, impairing results evaluation. The possible effect played by the lunar cycle on parturition timing has been supposed also for animals. In domestic animals, the process of domestication reduced the genetic diversity [15] and within a specific breed the genetic variability is also much lower, due to inbreeding.
Moreover, within a single farm, the climatic conditions, management, nutrition, and environmental conditions are uniform for all the animals. In equine husbandry there is the popular belief that delivery time could be influenced by the lunar cycle. A recent study on cows [15], showed a significant influence of the moon on spontaneous parturition.
The influence of the moon on living beings can be attributed to factors such as gravity and light changes and their supposed actions on hormonal production and regulation [16]. Due to the moving of the moon relatively to the earth and the sun, lunar days are not perfectly 24 hour-lasting and this, in turn, alters the light cycle [17]. Moreover, it was suggested that some cyclic variations related to the lunar cycle can be mediated by melatonin and endogenous steroids, with a release of neurohormones triggered by some factors, such as the electromagnetic radiation and/or the gravitational force of the moon [1].
Some authors [18] investigated the role of the moon at birth on behaviour and cognition in donkeys and found that a 10% linear correlated effect on learning ability played by the moon phase. One study assessed the possible effect played by the moon at mating on the proportion of male to female horse foals at birth [19] but did not find a relation between moon phase at mating and foal's sex.
In mammals, many parameters can influence the pregnancy length and, in turn, the occurrence of parturition.
Among them, maternal, fetal, environmental and genetic factors are listed. A previous study [20] investigated some factors affecting pregnancy length in jennies and found that pregnancy duration was influenced by foal's sex, but not by foal birth weight, year of parturition, month of ovulation and parturition, and by the jennies' age.

Materials and Methods
The project was approved by the Committee on

Lunar cycle
The lunar cycle was divided in the classical four phases: waxing crescent, waxing gibbous, waning gibbous, waning crescent, each one lasting about 7.4 days. Moon phase at ovulation and at foaling records were obtained from the Astronomical Observatory of Abruzzo.

Statistical analysis
Data about jennies' age at parturition, date of ovulation, date of parturition, foal sex and pregnancy

Effect of month of ovulation and of month of foaling on pregnancy length
The month in which ovulation occurred did not significantly influence the pregnancy length.

Effect of lunar phases on pregnancy length
Pregnancy length was not significantly influenced by lunar phases (p = 0.328), nor at ovulation (p = 0.152) neither at foaling (p = 0.216; table 3).

Discussion
The present study results showed that neither at ovulation nor at foaling, the lunar phases significantly influenced pregnancy length in 96 Martina Franca Jennies reared under uniform breeding and management conditions. This result is in contrast with recent findings in cows [15], in which the effect of moon phase was significantly associated with timing of spontaneous calving in Holstein cows, with increased births around full moon in multiparous, but not in nulliparous cows. Previously, [12] reported significant clusters of deliveries in relation to full moon in multiparous women, although they considered this data cautiously. In the present study, the retrospective analysis of data did not allow to assess the possible effect of lunar phases at ovulation and at foaling on primiparous and multiparous jennies, because this information was not available from the data records. According to the possible effect of month of ovulation on pregnancy length, it is to note that a significant influence of the month of breeding on gestation length was previously reported in the horse mare [33]. The age of jennies did not show influence on pregnancy length, in agreement with previous data from Martina Franca jennies [20], and Spanish donkeys [32], but in contrast with data from the horse mare [33].

Conclusions
In conclusion, results from the present study showed that, in Martina Franca jennies, reared in a single breeding farm in the south of Italy, the lunar phases at ovulation and at foaling did not influence pregnancy length. In addition, some other factors, such as the month of ovulation and of foaling, the jennies' age, and the foal's sex, did not influence pregnancy length, resulted, however very variable. Further studies are needed to clarify the reasons for this pregnancy length variability in Martina Franca donkey breed.

Funding
The present study has been carried out in the framework of the Project "Demetra" (Dipartimenti di