Dear Moshe,

Great question. Rav Yonasan Eybeschutz (18th century Prague) writes in his Sefer, Kreisi u'Pleisi, that normally after slaughtering an animal the reason blood streams out is because the veins and arteries are severed. But here, they were not severed, so blood didn't come out (1). Like the commentaries before him (2), he writes that the Chidush is that it is not a problem that there is no opportunity for Kisuy ha'Dam. If that is the case, one might suggest that there was a degree of blood, just not enough to spill on the ground.

Best wishes,

Yishai Rasowsky