Can vegans swallow?

Some people may ask themselves if vegans can swallow, and if sperm is vegan.

Short answer: yes, sperm is vegan.

The definition of veganism is:

"A philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose; and by extension, promotes the development and use of animal-free alternatives for the benefit of humans, animals and the environment. In dietary terms it denotes the practice of dispensing with all products derived wholly or partly from animals." - The Vegan Society, 1979[1]

Considering that sperm is not sentient, because it lacks every trait an organism would need to be sentient, such as having no central nervous system, there are no moral qualms in regards to consideration for semen.
Sperm does not have the ability to perceive or feel and they're not aware, let alone have subjective experiences, simply being singular cells (also called spermatozoon). There is no suffering involved when swallowing semen or ejaculating. So as long as the parties involved are consensual to whatever practices are done, there's no need to hold back.

To read further on this, feel free to check the bodily fluids section.