Grazing Habits of Livestock
Livestock are selective grazers, using their sense of smell to select the most
desirable plants. With uncontrolled grazing, they will always return to the most recent
regrowth and if allowed to continue, will overgraze these plants resulting in loss of the
most desirable plant species.
Livestock may vary in their ability to eat pasture forages. However, by regulating the
grazing time (days) and the time (days) for regrowth, it is possible to vary the height of
the forage and thus achieve the optimum bite size for the grazing animal.
For cattle, 4-8 inches is considered an ideal grazing height, as an animal can
obtain a good mouthfull of forage with each bite. Forage over 10 inches is considered too
high, as it is difficult for the animal to obtain a good mouthful. Plants less than 3
inches in height will not provide a good mouthful.
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Forage Needs
Cow/calf pairs require different quality and quantity of forage than do stocker or
feeder animals. A cow/calf unit can make good use of low quality forage while stockers
need higher quality. Forage demands are often determined as a percent of body weight. A
range of 2.5 per cent to 4 per cent of body weight (BW) is often used for beef animals to
account for maintenance, growth and feed wastage.
Stocking rates may be determined in this manner. For example, a 1500 lb. cow/calf pair
at 4 per cent of BW may require 60 lbs. of dry matter (DM) forage per day or 3.75 tons DM
for the season (125 days). A pasture capable of producing 3,000 lbs. of DM for the season,
would require 2.5 acres for that grazing unit.
Sheep are similar in their forage requirements to cattle and horses. Due to a
more inefficient digestive system they usually requires 15 per cent to 25 per cent more
forage. Goats browse different species and are often used in multiple species grazing
systems to make better use of the available forages including weeds and brush.
Stocking rates should always be conservative and be continuously monitored to avoid
lack of supply during times of drought.
Measuring or estimating the available forage in a pasture is the "Art" of the
grassland manager. Some tools, such as a pasture disk, are available to estimate available
forage.
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Planning Process
- Pasture Plan
To plan a grazing system for your pasture, you need a map or sketch of the existing
farm enterprise so that you can plan for the future.
On your sketch you will need the location of :
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Existing fields, (crop and pasture)
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Location of bush, streams, ditches, slopes, roads
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Location of all existing fences
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Location of old and new water sites
Aerial photos are very useful to provide an accurate picture of the topography as well
as the acres involved in each parcel.
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Pasture Quality and Quantity
Identify the quality of forage in all pasture areas and potential pasture areas.
Include seeded pasture, unimproved and bush pasture, seeded annuals, and crop residues
that could be pastured.
The next step is to estimate the potential productivity and the time when the forage is
available. This can be done by estimating the potential forage production (by measurement
or from a reference source) and converting this information to Animal Days per Acre or
Animal Unit Months (A.U.M.). Both systems are based upon an animal unit of 1,000 lbs. live
weight.
If you assume 1 A.U. will consume 26 lbs. of DM per day (2.6 per cent of BW), the
forage needs of one cow/calf pair will be 26 lbs. DM/day. A pasture rated at 5 AUM could
support 1 AUM for 5 grazing months.
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How Many Paddocks
There is no "ideal number" of paddocks in a grazing
system. The number of paddocks required in any grazing unit will depend upon the number of
grazing days in a period and the amount of rest required for plant recovery. More paddocks
will increase the control of the grazing animal, increase the stock density and reduce
selective grazing.
Rest Period/Grazing Period + No. Animal Groups = #Paddocks
Using this formula, if 30 days are required for regrowth, 5 days grazing per period and
1 herd, this would require 7 paddocks. For two herds, an additional paddock would be
required assuming a "follow the leader" grazing system.
Days grazing per period is varied according to size and quality of forage in a paddock.
For example, more days grazing per paddock for larger paddocks or those with tame forages
and less days for bush or native pastures or smaller paddocks.
Rest is the Key to grazing management. Sufficient time must be provided for the grazed
plant to recover before another grazing. The grazing manager is always looking ahead to
when the grazed paddocks will be ready for another grazing. Walk Your Pastures. It usually
takes a plant 20-40 days to recover from a grazing.
During the fast growing period of the season, 20 days or less may be required for
regrowth, however 40 or more days may be required during the slow growth periods. Many
tame forages will recover faster than some native species.
- Stock density
Stock density is the number of animals per acre in a single paddock
during a grazing period. For example, 50 head on 10 acres provides a stock density of 5
head/acre.
Varying the size of the paddocks will affect the stock density. Some grazing managers
with many paddocks prefer stock density of 20 head per acre or more to give greater
control.
Increasing the stock density on a pasture results in more uniform grazing, a more even
"clip" of the pasture as the selective grazing of the pasture is reduced.
Paddock size is determined by:
Number of Animals
Desired Stock Density
Variable Stock Density
With the seasonal growth curve of the pasture and the increasing demand of the
livestock during the season, varying the size, and the numbers of paddocks in a grazing
system is a common practice. The objective is to maintain the forage in a high-quality
vegetative state.
The fencing system, particularly temporary electric fencing, is used to vary the size
of the paddock. One option is to have a good perimeter fence and then use temporary
electric fencing to subdivide or "ration out" the required forage for the stock.
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