I've had three dogs when I was between 15 and 20, then later I started again around 27 or so, and had at least five dogs since then. One was a great dane, I had to be bent over a chair because I was too small for him sitting on my knees.
One (an English bull terrier) on many occasions. And I've given blowjobs to several others. I looked after a staffie on and off for a while and he used to get really excited when he could tell I was going to jerk him off (he'd usually be half out of his sheath already if he suspected). I used to jerk him off until he was hard and then squeeze him around the base of his knot, that got him squirting. Then I'd either suck him off or hold a glass under his dick until he was done so I could drink it. I did that maybe a dozen times. Also a border collie on a few occasions.