In every Pastures for Profit school or discussion about management intensive grazing, someone always ask: “How many acres do I need per cow?”
Or “How long can I graze a 20-acre field?”
Or “How big do my paddocks need to be?”
One quick look and you realize that all of these questions are asking the same thing.
Most people think of terms like stocking rate, stocking density, graziers arithmetic, or even forage budgeting.
The real question. On closer examination, these questions actually get to the heart of managing grazing: balancing what the animal needs with what is produced.
I am reminded of the observation that experienced graziers know what their animals require, observe what is going on in their pastures and plan what they need to do next accordingly.
There are two key parts of any answer to these questions. I want to focus on the first part, what do the animals have to eat or how much feed is out there?
The second part can be easier, how much forage do they need to eat?
Do you measure up? To determine how much feed is available, we must measure the forage.
Now, there are lots of ways to measure forage, pasture sticks, rising plate meters, electric pasture probes, and even the fun method of cut-dry-weigh.
With experience, graziers can consistently determine how much forage is available by walking their paddocks.
The easiest measurement of forage we can do is height. We see inches of forage.
But there seems to be some common confusion about using plant height to measure forage. Do livestock eat inches of forage or do they eat pounds of forage?
Actually, they eat pounds. To make it simpler, we take water out of the equation and say pounds of dry matter.
Take half? Using plant height has also confused a lot of people when we talk about the rule of thumb for forage management: Take Half: Leave Half.
I have heard speakers state that this refers to plant height. One example used was the grass is 10 inches tall at the start of grazing, then you should pull the animals out at 5 inches.
The rule of thumb ‘Take Half: Leave Half’ refers to dry matter, not inches.
If you really look at the profile of grass plants, you should notice that there is more vegetative matter the closer you get to the ground.
If you are ambitious, you could cut and weigh each inch of plant material from the ground up. Depending on the grass species, you would find that the first 2 to 3 inches has more dry matter than the next 6 to 10 inches.
Convert to dry matter. If height is the easiest measurement, then we have to convert plant height to pounds of dry matter.
There have been tables created that list different forages and pounds of dry matter expected per inch depending on the condition of the pasture. Those came from multiple observations of specific grasses.
But if you do not have those forages listed, which forage on the chart do you pick? I have been in fields looking at the chart on the stick with farmers and the grasses they have are not listed.
Another caution about using tables like that are the condition of the pasture. Pounds of forage per acre is also related to the density of the plants in the field. The pasture condition side of those tables try to get at density.
Which numbers should be used? This is a subjective measurement, one person may call a pasture poor and someone else calls it good.
Meters and probes. Rising plate meters and pasture probes try to account for both height and density. Both can be used for consistent estimations of forage dry matter. But they still need to be calibrated.
The calibration relies on the cut-dry-weigh method.
Back to cut-dry-weigh. The cut-dry-weigh method is simply to take a known area, usually a 2-foot square, cut all of the forage in that area, dry it down, weigh the sample and convert it to pounds of dry matter per acre.
It is the most accurate method we have to determine how much feed is out there in terms we can use.
Taking samples like that does take time, so most people use it to calibrate some other faster method of measurement, which is OK.
But sometimes I think we should teach it first and then move to the easier methods.
(Jeff McCutcheon is an OSU Extension, Agriculture and Natural Resources Agent in Knox County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)
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