Calf wont take bottle!?!?

How to get a 3 day old calf to take a bottle, momma is sick and unable to feed him so for the past couple days we've been havin to force feed him becuz he won't suck on the bottle...I've heard sometimes it can take a lil while but is there anything to do to make him take the bottle? I'm thinkin maybe its because he's weak but if he doesn't eat he's only gonna get weaker!