Sheep don’t send signals or stick to schedules, but ranchers still know exactly when mating happens. The secret is surprisingly simple.

Male sheep wear a special marking harness fitted with a colored chalk block on their chest. When a ram mounts a ewe, the chalk leaves a clear mark on her back. That single streak tells the rancher who was bred and roughly when.

The color is often changed every few weeks, allowing farmers to track breeding windows and predict lambing dates with impressive accuracy.

Ranchers also watch behavior closely. Ewes in heat will stand still for a ram, become more vocal, and show brief restlessness. Once bred, those signs disappear.

In some cases, a “teaser ram”—a male unable to reproduce—is used first to identify which ewes are fertile before introducing a breeding ram.

It’s practical, low-tech, and surprisingly precise. Long before ultrasound machines, shepherds had timing down to an art.