Agriculture & Life Sciences
I very much doubt this is true for life sciences. If any thing, you’d expect biology PhDs to be more Democratic than, say, physicists, because they’re much more female.
"Agriculture & Life Sciences" are collectively the degree programs you'd expect to only see at land-grant institutions. For example:
--Agricultural Economics
--Animal Science
--Crop Management
--Food Science & Technology
--Forestry
--Horticultural Sciences
--Nutrition
--Poultry Sciences
--Rangeland, Wildlife & Fisheries Management
--Recreation & Tourism Sciences
--Soil Sciences
--Veterinary Sciences
All these fields have in common that they're concerned with the management of land, plants and animals for human use (i.e., agriculture.) In contrast to biology, they involve an inherently interdisciplinary approach and tend to overwhelmingly attract students from agricultural/rural backgrounds (hence why they'd be Republican-leaning.)
I don't get the impression that
PhD holders in any of these fields outright lean R, at least in the Pacific Northwest. Then again I don't perceive Computer Science to be a particularly R field either.
