I applied directly on their website, and the next day I received phone call from recruiter to set up a phone interview. The interview consisted of describing all of your resume in detail, followed by two very basic behavioral questions ("tell me about a time you worked on a team project", etc.). The recruiter was nice enough, though sounded a little bored, and was typing the answers as you spoke them (she had to ask me to stop or slow down multiple times, which was a little annoying). Be prepared for very detailed follow-up questions on your answers. She then let me know she would send my file to the Purina plants for further consideration, and one would contact me if they wanted to interview me.
The next week, a plant e-mailed me letting me know they were going to fly me and other candidates out for a two-day on-site interview later that month. A current management trainee then e-mailed and called me, introduced himself and asked if I had any questions, which I thought was very helpful. The first day consisted of a plant tour, a presentation on the company and the program, followed by drinks and dinner with current management trainees. The whole day was very informal, fun, and really interesting, and they wanted to make sure all your questions were answered. The next day consisted of three one-on-one interviews with very general behavioral interview questions, most regarding working on a team, working closely with other people, etc. The interviewers, who we met the previous day, were very friendly and personable. Overall enjoyable experience, staff was very friendly and laid back. NPPC seems like a great company to work for. Three weeks later, I received a standard thanks-but-no-thanks e-mail with the subject line "Purina Rejection." Ouch.