A widely circulated internet meme (see e.g. the oatmeal) states that pig orgasms can last up to 30 minutes.
I've been trying to find any source or reference to back up (or refute) this claim, but haven't been able to find anything.
Pig ejaculation certainly does last a long time relative to human ejaculation, and pig ejaculation is measured in minutes, not seconds.
Boar semen is collected to artificially inseminate sows. I found various guides on collecting boar semen which contain estimates for how long one should expect ejaculation to last.
Here is one estimate from the Department of Animal Sciences Purdue University:
Always allow the boar to complete his ejaculation (5-8 minutes). If you let loose too soon, be prepared for a challenge. He will not want to leave the dummy. You will make this mistake only once or maybe twice.
The boar will generally go through two to three cycles during ejaculation, taking five to fifteen minutes to complete the process.
When the penis is 'locked' in the hand and the boar relaxes, a four-phase ejaculation follows in a few seconds, taking 5 to 10 minutes to complete.
Large amounts of gel signal the end of ejaculation. When it is clear the boar's erection is fading, a second ejaculation can be stimulated with brief, firm, pulsating hand pressure applied to his penis.
So the largest estimate is 15 minutes, then add a possible second ejaculation of 15 minutes, that might be where the 30 minute number came from. Of course it depends on the pig! There does seem to be a large variation. More likely, the slightly more conservative estimates given here are the length of an average pig orgasm.