There are very few reasons for mobs of livestock to have access to ponds beyond and emergency drinking water access. My reason here is that these heifers needed to be separated from the main cow herd for the 45 day breeding season and the only paddock I have does not have shade or even a high point to catch a breeze such as the pond dam where the heifers in the second photo are standing.
Ideally, allotting short term adequate shaded space is the optimal. Video below shows comfortable cows and calves.
In many cases, cattle not selected for heat tolerance will immerse themselves in a pond for relief. The flip side is that oftentimes these cattle will tolerate severe cold better than the others. We can spend decades selecting for the genetics which thrive in each of our unique environments and management. Hopefully also providing a quality eating experience for the consumer.