The website Biology On Line defines carrying capacity as the "largest number of individuals of a particular species that can survive over long periods of time in a given enviroment, this level depends on the effect of the limiting factors".
That is pretty much how we use it in animal husbandry- how many animals can we get onto a piece of land and have them survive from the available food. If we add suplimental feeding, then the carrying capacity goes up and we put more animals on the land. But there's a problem.
Recently I became aware of two facts here in Whatcom County, Washington, that are true in many areas. First, in looking at some aquifer maps, I saw that there are very high accumulations of Nitrate in groundwater around Lynden, a highly agricultural area here. The second fact was visual. Driving last week across the county I saw in several places huge impulse sprinklers spraying manure slurry onto the fields. This is a common practice as a means of getting rid of the manure from dairy operations and improving the fertility of the land, so it can produce good grass for the herds.
Do you see the problem? That manure is the source of the Nitrate in the groundwater. So, the land may be able to feed the animals, but it can't process the waste.
Which leads to the conclusion that carrying capacity should not just be about how many animals you can feed on a piece of land, but also how can the land process the waste products of the animals without destroying water quality.
Another way to look at this is to look at true costs of agriculture. The true cost would include removing the nitrate from the water that the animals contributed.
One way or another, we pay. If we use present land use definitions of carrying capacity, we pay for the treatment to remove the pollutants. If we restrict the number of animals to more accurately represent carrying capacity, the price of meat will go up. We pay with tax, or we pay at the store. Of course, the meat producers would prefer not to talk about it. If they don't have to pay a true cost of production, then they look like they are selling a good value, and the costs to fix the damage are managed by those all time favorite bad guys- the government.
If meat prices reflected the true cost, we probably wouldn't buy so much, which is a worry for the producers, but would benefit our aquifers, and for that matter our hearts.
Mass production of meat is a little like the fossil fuels business. there are lots of subsidies, tax breaks, and market tricks that camouflage the true cost. At the very least, we should push back the veils to see what our meat consumption really costs us in dollars and environmental impacts.