From your post, it sounds as if you're relatively new to hot snakes, so I'll try to help, though there are more knowledgable folks here than myself.
My experience with freshly caught c. horridus was that they needed the following items ...
One thig I need to say right off ...make sure he has adequate housing ... I absolutely HATE seeing large rattlers in a twenty-gallon aquarium, I don't care what anyone says. Many times, wild-caught venomous snakes need room and time to get settled in.
1. Check scales (especially underbelly) closely with light and magnifying glass to see if ticks or mites are present. Please note, if you don't have much experience pinning and necking large rattlers, get advice from someone who does. It's very easy to injure the snake. Even if you don't see ticks or mites, it might be a good idea to put a MINUTE (read very small) dusting of Sevin Dust (from hardware store) in the bottom of the cage under whatever substrate you use. Oh ... make sure the snake ain't in the cage when you do this.
2. While you've got him or her 'necked' check the snake (especially the 'business ends') for mouth rot, tumors, injuries, open sores, anything sticking out of it's butt (don't DO anything if something's sticking out, take it to a herp vet because it could have worms, prolapsed penisis or sump'n else). If you see open sore that aren't too bad/big regular applications of hydrogen peroxide with a q-tip will usually clear it up.
3. Get a stool sample to a vet to check for parasites ASIP (as soon as it poops).
4. Make sure the temperatures are correct in the cage. Take the temp AT THE SNAKES LEVEL IN THE CAGE, not at the top of the cage ... the snake ain't up there unless he's a climbing horridus (c. horridus climbus). Ensure that there are warmer and cooler spots in the cage so he can bask or cool down if he wants, but make sure the warm and cool areas are still within the optimum range for the snake.
5. Make sure he has a hiding place in the cage (a box, an overturned flowerpot or bucket with a hole in it, etc.) and isn't being messed with much, if at all. He's scared and he needs some space to calm down. Snakes are well-known for needing their 'quiet time'.
6. Also make sure he has periods of light and dark. You wouldn't want to be under a spotlight all the time either.
7. Make sure he is well-hydrated. I always likes a relatively shallow plant pot bottom. Those terra cotta thingees that go under a pot for excess water to run into. They are more shallow than most dog dishes and you can get them pretty wide, too. Make sure the water is kept clean. I always soaked my new catches in the tub (I covered all the drains and spouts) or in a large aquarium to ensure thay are well hydrated and it helped remove any nasties that might be clinging. Make sure the water is about 65-75 degrees and that there's no soap scum in the tub or aquarium you use. Disinfect whatever you put him in.
If all this has been done ... give the guy a week or two to calm down and acclimate to his new home. Give him some room and don't mess with him all the time. Just come in once per day (quietly) to check on him (remember you need his poop) and check his water and to cycle his light. Make sure he is in a low-traffic area so he isn't subject to movement and noise all the time. DO NOT FORCE FEED HIM yet ... give him some time with the previous conditions met first.
After two weeks of relative quiet time, give him a small, live mouse and sit very quietly and far away and watch to ensure the mouse doesn't try to bite on the snake if not taken. Give him an hour (you can read a book) or so and see if he feeds. If he kills, it VERY important that NO ONE is moving around at all in the room. Rattlers can be easily spooked (though some eat like PIGS from day one).
DON'T PUT ANOTHER SNAKE IN WITH HIM if he is already a trouble feeder. Just look after this guy for while and get him squared away before taking on another charge.
Following the previous items ... I have NEVER had a WC rattler not eventually feed. Some are just easily 'put off'.
Good luck!
Phil Minh Thong Holbrook