Edit: Although the banner advert on the site said free shipping ended at 0900am Thursday, as per @dankd, the coupon still seems to work if you add it manually so I've unexpired this deal. No idea when it will end, or if there's any chance Vet Post will cancel orders if they say it was a mistake.
Happened to notice while looking for something that Vet Post is offering free shipping with no minimum spend until 0900 tomorrow/Thursday. It should be automatically added when you checkout but I've provided the coupon code it uses. Fairly sure this means you can't use any other coupons.
VetPost normally has free shipping over $79 so this is most useful if you want to make a smaller order where shipping is $6. Also useful for rural delivery, when I tested a rural address still seemed to be completely free shipping (normally $5.50 more for light weighted rural delivery, so $5.50 if you spend more than $79).
Possibly it also works for heavy orders but I didn't test this.