Fig. 1

Seasonal-trend decomposition analysis of the body weights of male racehorses. The data are for male horses aged 2–7 years that competed in races held by the Japan Racing Association in the years 2002–2014 (n = 377,301). a The mean body weight of the horses by age and month. b The seasonal component. c The trend component. d The remainder component after fitting the seasonal and trend components. The dotted vertical lines indicate the month each year when body weight peaked, and the dashed vertical lines indicate the month when the body weight was at its nadir. The grey bars to the right of each panel show the relative scales of the components. Each grey bar represents the same length, but because the plots are on different scales, the bars vary in size