Carrying Capacity a Zero-sum Calculation

Beefs and Beliefs

For grazing think: forage production minus cattle consumption

Published on: January 19, 2012

I’ve had carrying capacity on the brain the last few days – mostly because I’ve been helping some friends cull deer/reduce deer numbers but also because of what I’ve seen across the countryside while traveling.

I live in Oklahoma, and though I was on the eastern edge of the worst part of the drought we still had half our normal rainfall. Further west it was worse.

Some of the country out there wasn’t destocked near early enough and it’s mostly bare soil. The damage will seem slight once it starts raining again and no one will notice the increased plant spacing, new erosion and deeper-cut creeks. They’ll just feed more hay.

I think the appearance of the land and the hanging onto cattle so long in drought signals the fundamental misunderstanding of the factors which make up stocking rate calculations.

It’s mostly mathematics and common sense. Simply put, you grow only so many tons of forage each year on your land and a bovine eats a given amount of forage each day and year, depending on size and production class. Cows eat about 3% of their body weight daily. Lighter cattle eat 2%, 2.5% or more daily, for example.

Multiply the number of cattle by the number of pounds consumed and you get the consumption side of the equation.

If you’ve never asked, stocking rate recommendations are basically founded on the “take half, leave half” principle. Range scientists figure on grazing about one-fourth the normal forage production, losing about one-fourth to trampling, weather and other issues, and leaving one half standing. It doesn’t work out exactly that way but that’s an argument for another time and place.

Essentially, it’s roughly production minus consumption, with allowance for leftovers. That’s the mathematical part.

But common sense is demanded. When it rains more, there’s excess and that presents opportunity. When it rains less there’s not enough and that means fewer head can graze.

It’s hard enough to manage from year to year; drought just adds a heavy emotional burden to the decision.

Yet it seems to me keeping in mind the fundamentals of grazing capacity as an equation is a useful mental tool: forage grown minus number of cattle grazing times forage consumed per head. It should help producers face hardships such as drought with more realism.

We can improve the land and increase forage production by good grazing management but we can’t get around the mathematical relationship of production minus consumption. Neither can we escape the ravages of overconsumption, not on the plants/rangeland and not on the animals.