Analysis of breeding records from a large, well managed Zebu cattle (BOS INDICUS) herd in the Mexican Gulf Coast area and calculation of Spearman rank correlations with local meteorological data (monthly means for temperature, pressure, precipitation, humidity) revealed significant seasonal fluctuations in reproductive functions. This seasonal influence was evident for the onset of puberty; for all consecutive conceptions and for all conceptions in relation to the length of the calving interval. Fertility maxima coincided with the onset of the rainy season (June to August), with significant rank correlations between conceptions and temperature (+ 0.827), pressure (− 0.751) and precipitation (+ 0.632). A second fertility maximum was revealed late in the dry season (February to May), showing significant effects during early puberty and in situations where conceptions after calving were delayed. No single meteorological factor was significantly rank correlated with this pre-rainy season effect.