For the last 5 - 6 months, I switched
over to a low carb (~ 50 - 75g / day) diet,
mostly making up the calories with whey protein and lots of fats (olive oil, avocado,
grass fed butter).
Mostly they depend on the grazing lands change
over time as they become unsuitable by the invasion of predators or large herds, drought, or
over-growth of
grasses.