I DID partcipate in the Belize Animal Science pre-veterinary program in 2007 and it was a GREAT experience for me! (I also got a FULL scholarship through my school for the entire trip + airfare, so see if your school has any programs like this.)
Keep in mind that I had *just* begun to consider switching from pre-med to pre-vet and I hadn't yet had any hands-on clinical veterinary experience. Many of the things we did during normal class hours (SQ, IM injections, drawing blood, physical exams, suturing workshops, feeding and caring for wildlife, horse training etc) would not have been ground-breaking for me now after working as a vet-tech for nearly 2 years. However, back then, it was an absolutely perfect way for me to test the waters and gain some basic hands-on experience.
I WILL say that a few of us did have the opportunity to castrate bulls, pigs and neuter a stray dog (and ride a lot of horses!) but some of this was done during weekend extracurricular activities, so there's no guarantees. Also, having worked as a tech in a dog/cat only small animal clinic, I do think that my trip to Belize exposed me to MANY aspects of rural medicine, large animal medicine, equine medicine, wildlife and exotic medicine that I would otherwise not have experienced (not to mention the perspective one gains when exposed to the disparities and hardships faced by vets in developing countries... forget about gas anesthesia, autoclaves, gloves etc.).
Regarding credit - many of my friends did receive academic credit for their classwork in Belize. I didn't bother because I was a biochem major in undergrad and I knew it wouldn't fulfil any of my requirements.
I actually blogged the 1st half of my trip. PM me if you want with your email address and I'll give you access to my blog.