[citation needed] For example, in 1960, psychologist John Falk was studying hungry rats that had been trained to press a lever for a small food pellet.
Once a rat had received a pellet, it was obliged to wait an average of one minute before another press of the lever would be rewarded.
Pregnant sows are typically fed only a fraction of the amount of food they would consume by choice, and they remain hungry for almost the whole day.
If a water dispenser is available, some sows will drink two or three times their normal daily intake, and under winter conditions, warming this amount of cold water to body temperature, only to discharge it as dilute urine, involves an appreciable caloric cost.
However, if such sows are given a bulky high-fibre food (which under typical circumstances would result in an increase in water intake), they spend much longer eating, and the excessive drinking largely disappears.