Motherhusk for some reason works on anal pregnancies, but in order for it to take effect, you must first have a vagina. Then, once you are impregnated anally, the pregnancy modifier from the vagina mysteriously seems to apply to the ass out of nowhere. This can be tested with creatures that impregnate via the butt, such as butt bugs, or pretty much any impregnator on Myrellion since it's all eggs with a single live birth on there(most notably being the Water Queen pregnancy which is counted). Most interestingly, when trying to use Motherhusk on a male, it doesn't allow them to gain anything. No taint, no pregnancy speed increase, just absolutely nothing. I'm guessing this was due to how back then there was no anal pregnancies, which tbf there really isn't much content for either way as the only way to reliably increase anal capacity is to turn Kiro into a bimbo, trappify yourself via Carver's sluttificaion program, or take mods/drugs that drastically alter your body and/or give extra taint.
The test method is rather simple. If your character has a vagina, use 8 motherhusk. After that, remove the vagina. The pregnancy speed modifier will still apply to the butt with or without the vagina.
The test method is rather simple. If your character has a vagina, use 8 motherhusk. After that, remove the vagina. The pregnancy speed modifier will still apply to the butt with or without the vagina.