Is the Mare in Labor?
Mares tend to deliver their foals when it is dark out, but some will foal in the daylight hours. Odds are very high the mare will go into labor within the 4 hour window (on a 12 hour cycle) determined during prior monitoring as the foaling window. (See above regarding a foaling window.)
A horse can doze on her feet, but will lie down for a deep sleep. When a mare is large with foal she'll sometimes lie down just to rest and take some weight off her feet and legs. Lying down does not necessarily indicate the mare is foaling. In fact, there are a few mares who will push the foal out while still standing. Some mares move their legs while they are asleep.
Stage 1 labor is often when the mare shows more discomfort, including: pawing, pacing, rubbing her tail against the wall, kicking or nipping at her belly, etc. Less obvious indications are shaking or rubbing the head, working her mouth, swishing her tail, carrying her tail more away from her body, not standing still very long, etc. The mare may not eat if she is uncomfortable, which may mean the foal is in an awkward position ... or may mean the mare is in labor. But a seasoned broodmare may walk away from dinner to push out her foal.
The mare in Stage 1 labor normally has softer, sometimes runny manure. It is common to have multiple rather wet manure piles in the stall over a period of a few hours when the mare is in labor. Sometimes the manure is so soft and wet it more closely resembles a cow pie.
If a mare is very close to stage 2, it isn’t unusual for that mare to lie down briefly, stand, then lie down again moments later, perhaps repeating this several times. Sometimes a mare will roll to help the foal position better for delivery.
Each mare's behavior during labor is a bit different. Some are more obvious than others. The mare with a radical change in her behavior - or a prolonged stage 1 or 2 labor - may be having problems. The foal may be somehow positioned wrong and may need assistance. Most mares have no problems and can safely produce their foal unassisted.
Disturbing the mare while she is in Stage 1 labor may cause the mare to delay or even temporarily shut down the labor. Going to the stall to check the mare or clean the stall may result in stalled or stopped labor, but may also be advantageous if it appears the mare needs help positioning her foal.