IIRC they report horse weights for bettors to see when they place their bets. What people tend to pay attention to are the change in weights (compared to the horse's weight on its previous race). Major weight changes usually indicate that horse isn't going to perform well.

The real-life Sweek gained a hefty amount of weight that he had to slim off. Exactly 16 kg, IIRC.

On this subject... the current JRA record is like +66kg for a horse named Bonding Time. That horse finished at 15th.

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Anyway... looks like the umagirls are walking physics-middle-finger-defying monstrosities like the shipgirls.