I'm an agricultural economics major, all of my instructors are Republicans.
Out of curiosity, do they tend to vote GOP because of the party's general friendliness toward agriculture, or more based on social issues/military/"rural culture" generically?
Its a healthy mixture of both, but the former probably helps with keeping the department so overwhelmingly GOP.
Another hypothesis I have as to why nursing/business/ag professors tend to be far more conservative than the average professor is that many of them (at least in business I know) spent at least some time in the private sector, unlike the vast majority of others in academia. Is this true for the ag professors you had? I assume most of them grew up on a farm (or worked on it as a kid), but do many also manage land in addition to teaching?
I can only speak to one field of business (finance), but I don't think I had a single professor (i.e., not a TA) who didn't have private sector experience. All seemed to be fiscally-motivated Republicans.