Animal drinking troughs have pressure reducers for reducing the higher pressure of the liquid supply to a low liquid pressure for supplying the animal drinking troughs. For various reasons, it is desired to change the reduced pressure. This takes place by adjustment of the pressure reducers. It is known to undertake such an adjustment with compressed air. This requires a separate compressed air source and a corresponding pipe system. The invention makes provision to adjust the pressure reducer hydraulically by means of the higher pressure of the liquid of the liquid supply. The energy required for adjusting the pressure reducers thereby provides the liquid pressure of the liquid supply. As a result, the pressure reducers according to the invention operate autonomously. A separate energy source for adjusting the pressure reducers is not required.