Does he act hungry? Is there possibly some underlying condition where it's painful for him to want to latch on? Tubing should only be a last resort if absolutely nothing is working and if he's truly getting dehydrated. And at that age, he is going to be a little bit of a fighter.
Another Q: Do you have other cows around that have mothered up to him when you're not there where he can reach through the fence and suckle at? Or, do you have a surrogate cow (or even goat) on hand where he may be more successful at mothering up with, if possible?
You might try and see if you can get him to drink out of a bucket. I had an older calf that I had to pull and hand raise, but bottles never worked. He'd throw himself around, up and down, and would never suck-I would squeeze the contents into his mouth and sometimes he'd swallow, other times it'd run out the side. I tried a bucket and he took to it right away and never looked back.
We've mixed liquid molasses in it before to improve the taste and even dipped the nipple in it first. Worked well. I'll update if I think of anything else. Good luck!
That’s a bit odd. A calf at that age being so resistant! I would suspect something is up with that calf. I always say a hungry calf will drink, because everyone I’ve had will after they get super hungry, eat.
My experience has been with getting critters on bottles: #1, they can be very picky with the formula; #2, they can be very picky with the nipple. I've actually had a doe go THREE days with absolutely nothing to eat, she was starting the downhill starvation slide; I could hear her tummy rumble, and she would always try the bottle, but immediately reject it. I finally got the bright idea to try a different formula (which thankfully I had on hand), and she immediately downed it! I've had the same thing happen over various nipples, as well--two sibblings like one, the third sibbling wanted nothing to do with it, but would take a different kind readily. Go figure!
With a calf, there's pretty much only one nipple type, unless you've been lucky enough to have others in your area (if so, buy one of each and try them all). So try getting milk on your fingers and see if he'll readily try suckling from your fingers (if so, suspect the nipple as the problem), and try offering it to him from a bucket. If neither of those approaches helps at all, try different formulas. I've had a lot of success with Dumor brand. I actually just this week had 5 kids on bottles that loved it, but I couldn't get any more, so I had to switch brands. Once they were fully on the other, they all but one began refusing it! You can also try whole cow's milk, preferably from a cow but also from the store (if from the store, try to find as close to natural as possible, like non-homogenized, minimally pasteurized--try NOT to use ULTRA pasteurized, it actually changes the protein molecules and makes it hard to digest--not making that up, had that experience with a kid, nearly killed her). You can also make an electrolyte solution with sugar, salt, and baking soda (Google it), and taste it before giving it, it should taste nicely sweet and pretty palatable. See if he'll take that. If so, it's not the nipple, but most likely your formula he doesn't want. (Consequently, taste your formulas. Some taste markedly better than others. If they taste gross to you, they'll probably taste gross to them, also, though individuals have varying tastes of course.)
Good luck! Getting a baby on a bottle can be uber frustrating, but once you finally find that sweet spot and he goes to town on it, it's SO rewarding!