Measuring pasture yield

By Gary Sliworsky
OMAFRA Rep.

Measuring pasture yields can be a challenge. The following article by Jack Kyle, Grazier Specialist with OMAFRA. Gives you an idea of how to do it.
With harvested forage or grain crops we get an indication of yield from the number of bales, feet in the silo or bushels of grain produced. With pasture we can measure the number of pounds of beef or lamb produced, but in many cases it is breeding females that are being pastured, so although we get an idea of the pounds of calf produced it is not a very accurate estimation of the actual pasture yields.
In many areas the productivity of a pasture is measured in terms of AUMs (Animal Unit Months), which is based on carrying capacity. An Animal Unit (AU) is considered to be 1000 pounds of beef cow with or without a nursing calf. Other animal types also fit under this definition based on 1000 pounds of body weight. The number of months (M) that this animal unit can be fed on the pasture gives the AUMs. This measure gives a good indication of the carrying capacity or productivity of the pasture.
Let’s look at an example: 10 cows weighing 1500 lbs would represent 15 animal units ...
If they were on a pasture for 60 days that would represent 2 months, 15AU X 2M is 30 AUM’s on that pasture. Let’s consider this value on an acreage basis. If this example was a 15 acre pasture then we would have (30 AUM / 15 ac) 2 AUM’s per acre. If it was a 20 acre pasture we would have 1.5 AUMs per acre. Another example: 10 stockers weighing an average of 500 pounds would represent 5 Animal Units. If they pastured for 120 days that would be (5AU X 4M) 20 AUMs. If this pasture was 5 acres then we would have 4 AUMs per acre.
By converting the animals into 1000 pound units you then have a consistent measure that will allow you to compare pastures, seasons and years.
Additional information can be found at the following website:
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/faq6722?opendocument
Another measure that can be used is cow days per acre. If 30 cows were on 20 acres for 90 days then we would have 30 X 90 =2700 cow days. 2700 cow days on 20 acres represents 2700/20 or 135 cow days per acre. This may be easier to calculate but it does not take into account the size of the cows.
The important part of this exercise is to record the number and size of animals that are in the pasture and the number of days that they are there. This is a very important measurement when looking at the productivity of annual crops such as turnips or cereals planted for grazing.

Dates to Remember
Dec. 3-5 – Large animal clinic dates for Dr. Stacey Angus. Call 204-422-8749 to book an appointment.