Last week, a group of friends and I went to spend our vacation in Colorado. We saw so many cool and interesting landscapes that we simply do not have here in Ohio.
One site that stood out to me was the rangelands on which they were running their cattle. It was very dry compared to the ones in Jackson County.
I looked to my friends and jokingly said, “See these hundreds of acres, I bet at least two cows can eat here for a month!”
My friends did not grow up in the agricultural world, so they missed the joke. This encouraged me to revisit the difference between stock density and stocking rate.
Stocking rate
These two concepts are very similar but different. Stocking rate is the number of animals on a piece of land, usually over the whole farm. Stocking rate is calculated by: Total Amount of Land / Number of Animal Units = Stocking Rate.
There is still another definition we need to know before understanding this concept. According to the Natural Resources Conservation Service, “an animal unit (AU) is one mature cow of approximately 1,000 pounds and a calf up to weaning, usually six months of age, or their equivalent.”
Let’s do an example: we have 100 acres with 20 cows. If each cow is 1 AU, our stocking rate is 5 acres/AU (100 / 20 = 5).
Stocking density
Stock density is the number of animal units that are occupying a specific paddock at that specific moment. Stock density is calculated by: Paddock Size / Number of Animal Units = Stock Density.
Let’s use the same example of 20 cows on the 100-acre farm, but the farm is split into four paddocks. Our new equation would be (100 / 4) / 20 = 1.25 acre/AU.
Now the big question is, how many animal units can my pasture support? The answer is, it depends. Let’s revisit the definition of animal unit. This definition assumes that the cow will consume 26 pounds of dry matter a day. This begs the question: how much dry matter is in my pasture?
Get a grazing stick
This is where I encourage everyone running livestock to own a grazing stick. This stick tells you a vast amount of information, but to keep this article short, I will sum up the use in this example. I take my grazing stick into my pasture and slide it into my tall fescue. I stand up and see two dots (grass covers eight of the 10 dots from my sight). I rotate my grazing stick to see that it says, “Estimated pounds of dry matter/acre/inch”.
This tells me that for every inch of fescue, I have 200 to 250 pounds of dry matter/acre. If I have eight inches of fescue, I have roughly 1,600 to 2,000 pounds of dry matter/acre.
I want to stop grazing when my fescue is 4 inches, so I have roughly 800 to 1,000 pounds of dry matter/acre to feed. Let’s use the same example: I am running 20 cows that eat around 26 pounds of dry matter a day. They consume 520 pounds of dry matter a day. They are in a 25-acre paddock, so they have between 20,000 and 25,000 pounds of dry matter to consume before rotating them.
This means they have about 38 to 48 days before rotating to the other paddock under continuous grazing.
The same calculations can be made for more intensive grazing in smaller paddocks.
There are other variables that exist, like utilization of the paddocks, but doing this math gives you a good estimation to help with your active management.
