Month and lunar cycle at calving influence and reproductive performance of a tropical buffalo herd

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A retrospective study (2000-2022) was conducted in a commercial buffalo farm in Mérida State, Venezuela, to assess the effect of month and lunar cycle at calving on some reproductive variables. According to the percentage of moonlight, the lunar cycle (29.52 days) was divided into 30 periods (0.98 days each). The intervals calving-estrus and calving-conception and the number of services/conception were analyzed by the general linear model. The conception rate at first service and calving frequency were analyzed by the Chi-square test (n=3510). The month of parturition did not affect the calving-estrus interval (p=0.1438), which varied between 93.3 (January) and 112.5 days (February). An effect of month of parturition was observed in the calving- conception interval (p=0.0006), with the greatest value in February (170.4 ± 11.3 days) and lowest values in January (137.7 ± 6.3 days), July (138.9 ± 7.3 days) and August (136.1 ± 5.4); however, no differences were found in the services/conception (p=0.4692) (1.41 in July and August, and 1.49 in June) and first service conception rate (p=0.8504) (∼63% in May and June, and 68% in January). The distribution of calving varied significantly along the year (p<0.0001); the lowest frequency of calving occurred between February and July (range 6.7 to 7.2%), and the greatest took place between August and January (9.6 to 10.9%). There was no effect of the lunar cycle at parturition on the calving-estrus interval (p=0.3837). However, there was an effect on the calving-conception interval (p=0.0021), which was more significant around the new moon (154.9 ± 4.5 days) than around the full moon (141.9 ± 4.0 days) and most of the waning period (138.0 ± 4.3 days). No effect of the lunar cycle was observed on services/conception (p=0.8196) or first service conception rate (p=0.8539). As has been observed in other species (cattle, swine, and guinea pigs), the frequency of calving was significantly greater (p=0.0026) ∼2 days around the new moon (17.5%) and full moon (14.6%) than in the remaining 26 periods of the moon cycle (67.9%). This study showed a significant effect of month and lunar cycle at calving on calving-conception interval and calving frequency in a tropical buffalo population.