Also, fwirw, once you have established a sow being in heat, mark it on your calendar. In roughly 2 weeks, they'll be back in heat again like clock-work, though it
can vary by a couple days, so you'll know beforehand it's coming.
All 5 of my sows are are almost exactly every 14 days, and all 5 go through their humping period, and all 5 have synced up within a day or so of the other, so it's like a full week of that silliness.
The one that "seems" in distress (one being mounted), is doing EXACTLY what female gp do when a boar is trying to get with them, usually followed by streams of urine aimed at the offending humper wannabe to discourage him/her and say "not ready", following an eventual bum up in the air when ready, though the one doing the humping (when it's a sow) is the one that's ACTUALLY "ready" to be mounted, hence the mention of a boar immediately mounting it if one was available, as mentioned in my last post. She would/should immediately put her bum up for him, or they'll do a short circle chase like they are chasing each other's bum in a circle like a dog chasing it's own tail, then mount.
Other things the "mountee" will do is get really low to the ground- chin and all, squeal slightly differently, similar to their whining when not wanting to be handled atm, along with "double-tap" nipping i.e. "nip nip"' running away then immediately following the offending humper' dropping their chin to the ground when being approached while also emitting a different squeal/wheek; spraying a stream of urine directly behind them; jumping the back legs up when their fur is nudged against the grain on the lower back/bum area; doing 180 jump/spins to face the other, etc.. ALL NORMAL
