If the goal is “maximum sustainable profit / ha” there are only two options in terms of grazing: Either we selectively graze the “top third”
Or we non-selectively graze and flatten the ground in order to achieve 100% harvest efficiency.
There are grazing management advisers that recommend ranchers to graze “lightly” or “take the top third.” This is IMPOSSIBLE in multi-species pastures. Cattle will, if allowed (low stock density), graze grasses selectively in accordance with their preference. They may utilise a third of the available material, but they will not evenly graze a third of each individual grass. The result of grazing selectively is poor utilisation (lower stocking rate) and negative species composition changes. There will also be a poorer cycling of nutrients as well as poorer solar energy conversion.
My advice is graze non-selectively and mitigate a drop in body condition by implementing a shorter recovery period (higher quality grass) during periods when body condition is critical (calving and breeding). An important proviso is that grazing be non-selective and that such intensively grazed areas be allowed a longer recovery period the following growing season.
The human mind is an enigma. It is amazing how we become brainwashed. The recommendation to “only graze the top third” is a case in point.