I am not quite sure what you mean. The amount of sperm in semen is microscopic.
Can you feel a man ejaculate during anal sex? Probably not. Just like the top of your vagina the rectum does not have a lot of nerve endings. You will probably be able to feel same heat from the ejaculate but even this is doubtful.
It will definitely drip and ooze out and make a considerable mess so you will feel it afterward.
It's much easier for me to feel a man ejaculating when I'm having anal sex. I'm just much more aware the tension in my anus than the mouth of my vagina. I can also feel the warmth of his ejaculation when he cums.