How to Determine How Many Acres of Pasture are Required For Your Cattle
Calculate how many animal units you have., Calculate the estimated stocking rate for your area., Determine how long your cows will be grazing on a piece of land for., Put it all together to find how just how much space you need for your herd., Find...
Step-by-Step Guide
-
Step 1: Calculate how many animal units you have.
In order to do this, you first need to know just how many animals you actually have, plus the average weight of the herd.
For example, you may have 100 head of 1400 lb mature cows.
The next thing you need to know is what an "animal unit" is.
Animal units (AU) are the basis of calculating stocking rates and pasture space for a group of animals.
The standard single (1) AU is equivalent to one cow-calf pair weighing a collective 1000 lb.
Some sources may confuse you with "with or without a calf" or as just a cow, but you should not worry about those technicalities so much as that 1 AU = one 1000 lb cow (or cow-calf pair).
To calculate the number of animal units you have, multiply the number of head by the animal unit equivalent of your cows.
By the example above: 100 cows x (1400 lb / 1000 ) = 100 head x
1.4 AUE = 140 AUs An "animal unit equivalent" is the adjustment that is calculated from the standard animal unit based on the average weight of your livestock.
AUEs can be used for any weight of grazing animal being used on the pasture, from sheep to bulls to horses to deer.
The calculation simply involves dividing the average weight of your animals by the weight of the standard animal unit. -
Step 2: Calculate the estimated stocking rate for your area.
The stocking rate for your location is determined by the amount of forage you have in terms of pounds per acre or kilograms per hectare, the utilization rate expected by the animals based on pasture condition, and how much of that forage is utilized by a standard animal unit for one month.
The amount of forage you have in your pastures can be eye-balled, though if you have not learned how to properly eye-ball how much forage you have, you can be far more in accurate than if you clipped various samples around the pasture, and weighed then after they are dried down.
To get an accurate clipping measurement, you need to use a 1 ft by 1 ft quadrat (square) so that you can calculate the amount of forage (in pounds) per acre (where 1 acre = 43,560 square feet) after its dry matter weight has been assessed.
Utilization rate is a percentage of how much a cow should remove compared with the total amount of forage that is actually there.
For most pastures that are in decent condition (with 6 to 8 inches of forage or more) the utilization rate should not exceed 55%.
Poorer pastures with low amounts of herbage should have a utilization rate of less than 30%.
Excellent pastures can have a high utilization rate only if the animals are in there for a short amount of time; otherwise it is best to stick with a 50 to 55% utilization rate to ensure plenty of plant material is left behind.
One AU is estimated to consume between 600 to 900 lb of forage in one month.
To make things simpler, and as an average used by all stockmen to calculate their stocking rate for their land, the best estimate is that one animal unit will consume 800 pounds of forage in one month.
This is what makes an Animal Unit Month (AUM).
To calculate out stocking rate, let's assume your pastures are producing 1600 pounds of forage per acre.
With a 50% utilization rate, and assuming one AUM consumes 800 pounds of forage a month, that will give you a stocking rate of
1.0 AUM/acre.
The formula is:
Stocking Rate = (Forage production x )/800 lb/month Per the example:
Stocking rate = (1600 lb/acre x (50%/100))/800 lb/month =
1.0 AUM/acre , Typically this is measured by months, not days.
For most North American areas (not including the tropics) a typical grazing season is between 4 to 6 months.
More southern grassland areas, like in California and down into Florida and Texas, are more flexible with being able to graze for 12 months a year.
Thus, let's assume you live an area where you are only wanting to graze these 100 cows (see step 1 above) for 4 months.
Only use days if you are splitting up the pasture into multiple paddocks to rotationally graze your cattle in.
This requires more extensive calculations, and an entirely different how-to article to perform. , Once you have figured out how many head of cattle you have, their weights and corresponding animal units, your stocking rate, and how long you intend to graze, you can plug them into a formula to get the amount of land needed for your herd.
The formula is:
Required Pasture = (Number of Animal Units x Stocking rate ) / Time to graze Using the example created:
Required Pasture = (140 AUs x
1.0 AUM/acre) / 4 months = 560 acres needed. , You may need to recalculate if you cannot get the amount of acreage for your herd.
Recalculation may involve reducing the number of cows, or the amount of time they spend in the pasture.
It's highly recommended to not change the weights of your cows if you've already determined their weights, because you could short-change both yourself and the person you may be leasing the land from to use to feed your cows for the summer.
If you reduce the weight of your cows from 1400 pounds to 1200 pounds, you may be inviting serious overgrazing by libelling about your cows' actual average weights.
This could land you into trouble and potential for being not allowed to lease from that person again.
Also do not change stocking rate unless you're absolutely sure that it needs to be changed.
Always remember, the shorter the grasses look and the thinner the sward (collective term for lots of forage plants), the lower the stocking rate will be.
If you reduce the number of cows you have or the time allowed to graze, you can reduce the amount of land needed to raise your animals on.
For instance, 90 head of 1400 lb cows can be grazed on 504 acres of land, whereas if you decided to graze your 100 head of 1400 lb cows for only 2 months, you could leave your cows on 280 acres for two months. , Keep an eye on the pasture and the cows.
If you find they are not getting enough, you may need to pull them out sooner than expected.
These calculations are merely a guide and an estimation.
They are not exact, nor ever will be.
It's up to you, as manager, to pay attention to the resource (forage) the cows need in order to both keep your cows happy, and not cause significant damage to the land. -
Step 3: Determine how long your cows will be grazing on a piece of land for.
-
Step 4: Put it all together to find how just how much space you need for your herd.
-
Step 5: Find out if you can get the required space for your livestock.
-
Step 6: Turn your cows out to pasture and let them graze for the allotted time.
Detailed Guide
In order to do this, you first need to know just how many animals you actually have, plus the average weight of the herd.
For example, you may have 100 head of 1400 lb mature cows.
The next thing you need to know is what an "animal unit" is.
Animal units (AU) are the basis of calculating stocking rates and pasture space for a group of animals.
The standard single (1) AU is equivalent to one cow-calf pair weighing a collective 1000 lb.
Some sources may confuse you with "with or without a calf" or as just a cow, but you should not worry about those technicalities so much as that 1 AU = one 1000 lb cow (or cow-calf pair).
To calculate the number of animal units you have, multiply the number of head by the animal unit equivalent of your cows.
By the example above: 100 cows x (1400 lb / 1000 ) = 100 head x
1.4 AUE = 140 AUs An "animal unit equivalent" is the adjustment that is calculated from the standard animal unit based on the average weight of your livestock.
AUEs can be used for any weight of grazing animal being used on the pasture, from sheep to bulls to horses to deer.
The calculation simply involves dividing the average weight of your animals by the weight of the standard animal unit.
The stocking rate for your location is determined by the amount of forage you have in terms of pounds per acre or kilograms per hectare, the utilization rate expected by the animals based on pasture condition, and how much of that forage is utilized by a standard animal unit for one month.
The amount of forage you have in your pastures can be eye-balled, though if you have not learned how to properly eye-ball how much forage you have, you can be far more in accurate than if you clipped various samples around the pasture, and weighed then after they are dried down.
To get an accurate clipping measurement, you need to use a 1 ft by 1 ft quadrat (square) so that you can calculate the amount of forage (in pounds) per acre (where 1 acre = 43,560 square feet) after its dry matter weight has been assessed.
Utilization rate is a percentage of how much a cow should remove compared with the total amount of forage that is actually there.
For most pastures that are in decent condition (with 6 to 8 inches of forage or more) the utilization rate should not exceed 55%.
Poorer pastures with low amounts of herbage should have a utilization rate of less than 30%.
Excellent pastures can have a high utilization rate only if the animals are in there for a short amount of time; otherwise it is best to stick with a 50 to 55% utilization rate to ensure plenty of plant material is left behind.
One AU is estimated to consume between 600 to 900 lb of forage in one month.
To make things simpler, and as an average used by all stockmen to calculate their stocking rate for their land, the best estimate is that one animal unit will consume 800 pounds of forage in one month.
This is what makes an Animal Unit Month (AUM).
To calculate out stocking rate, let's assume your pastures are producing 1600 pounds of forage per acre.
With a 50% utilization rate, and assuming one AUM consumes 800 pounds of forage a month, that will give you a stocking rate of
1.0 AUM/acre.
The formula is:
Stocking Rate = (Forage production x )/800 lb/month Per the example:
Stocking rate = (1600 lb/acre x (50%/100))/800 lb/month =
1.0 AUM/acre , Typically this is measured by months, not days.
For most North American areas (not including the tropics) a typical grazing season is between 4 to 6 months.
More southern grassland areas, like in California and down into Florida and Texas, are more flexible with being able to graze for 12 months a year.
Thus, let's assume you live an area where you are only wanting to graze these 100 cows (see step 1 above) for 4 months.
Only use days if you are splitting up the pasture into multiple paddocks to rotationally graze your cattle in.
This requires more extensive calculations, and an entirely different how-to article to perform. , Once you have figured out how many head of cattle you have, their weights and corresponding animal units, your stocking rate, and how long you intend to graze, you can plug them into a formula to get the amount of land needed for your herd.
The formula is:
Required Pasture = (Number of Animal Units x Stocking rate ) / Time to graze Using the example created:
Required Pasture = (140 AUs x
1.0 AUM/acre) / 4 months = 560 acres needed. , You may need to recalculate if you cannot get the amount of acreage for your herd.
Recalculation may involve reducing the number of cows, or the amount of time they spend in the pasture.
It's highly recommended to not change the weights of your cows if you've already determined their weights, because you could short-change both yourself and the person you may be leasing the land from to use to feed your cows for the summer.
If you reduce the weight of your cows from 1400 pounds to 1200 pounds, you may be inviting serious overgrazing by libelling about your cows' actual average weights.
This could land you into trouble and potential for being not allowed to lease from that person again.
Also do not change stocking rate unless you're absolutely sure that it needs to be changed.
Always remember, the shorter the grasses look and the thinner the sward (collective term for lots of forage plants), the lower the stocking rate will be.
If you reduce the number of cows you have or the time allowed to graze, you can reduce the amount of land needed to raise your animals on.
For instance, 90 head of 1400 lb cows can be grazed on 504 acres of land, whereas if you decided to graze your 100 head of 1400 lb cows for only 2 months, you could leave your cows on 280 acres for two months. , Keep an eye on the pasture and the cows.
If you find they are not getting enough, you may need to pull them out sooner than expected.
These calculations are merely a guide and an estimation.
They are not exact, nor ever will be.
It's up to you, as manager, to pay attention to the resource (forage) the cows need in order to both keep your cows happy, and not cause significant damage to the land.
About the Author
Helen Reed
Writer and educator with a focus on practical organization knowledge.
Rate This Guide
How helpful was this guide? Click to rate: