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Introduction Non-uniform grazing distribution by livestock on diverse landscapes
and its effects on present vegetation has presented a challenge for livestock, grazing,
and natural resource managers for an extended period of time. Many variables, such as
water location, forage availability, and ruggedness of the terrain, which exist at a
variety of scales, influence habitat selection and use behaviors by livestock. As a
result, livestock tend to use some areas more than others, resulting in degradation of the
plant communities that are used heavily throughout the grazing period.
Animal age, a variable that has been researched very little
in relation to livestock distribution, is highly related to an animal’s physical,
physiological, and morphological characteristics. Understanding how these factors may
interact to influence the grazing behaviors of animals of different ages may help managers
create tools to reduce the negative effects of heavy use in some areas and little or no
use in other areas of a pasture. One question still exists, “Can you teach an
old cow, sheep, or goat new tricks?”.
How Does Vegetation Respond To Non-Uniform Livestock
Grazing?
Large herbivores play a major role in the dynamics and
function of ecosystems by selectively consuming some plants within certain plant
communities in a pasture. A decline in range condition due to direct and indirect effects
of heavy, prolonged grazing on certain sites within a landscape may cause a shift in
forage production and/or species composition in these areas. It is important to keep in
mind that some level of patchiness is good for increased biodiversity of plants and
animals on a landscape level. However, excessive use or lack of use of plants and patches
across the landscape may be unfavorable to the overall sustainability of plant
communities. Therefore, knowledge and implementation of management practices, such as
grazing with intraspecific age classes of livestock (i.e. various ages of the same kind of
animals grazing together), that enhance some level of diversity but minimize excessive
selection and degradation of resource patches is critical.
What Animal Characteristics Affect Distribution?
Little research to date has focused directly on
intraspecific age differences related to landscape- or community-level resource selection
patterns by livestock. All factors that influence livestock resource selection behaviors
are highly interrelated. Therefore, it is important to understand how age relates to
physical, physiological, and morphological characteristics of an animal and how they all
relate to each other to influence animal grazing behaviors.
Physiology and Body Size.
As age and body size are directly related, physiological differences between ages must
also take into account differences in body size. Younger, smaller animals have greater
energy and nutrient requirements per unit body weight, smaller rumen capacity, and,
subsequently, lower absolute intakes of forage than larger, older animals. The combination
of a smaller rumen capacity and greater nutritional requirements per unit body weight
requires smaller, younger animals to consume higher quality diets within a foraging bout
than larger, older animals. Additionally, lactating cows, those that are producing milk to
feed their young, tend to consume more forage per unit body weight than non-lactating cows
to satisfy greater energy and nutrient requirements.
Thermoregulation.
Animals must maintain a constant body temperature, which is called thermoregulation,
despite any challenges from their surrounding environment. Winter grazing studies
conducted in Montana, have documented young cattle, which have higher thermoregulatory
needs than older cattle, using pastures less efficiently, spending more time in cold,
windy, unprotected areas, and grazing longer and traveling farther per day than older
animals. This difference may be due to a lack of grazing experience of young cattle in
winter pastures and higher nutrient and energy demands when compared to experienced,
mature cows.
Foraging Time and
Efficiency. Under more moderate environmental conditions, young cattle
and goats have been documented grazing longer than older animals each day and spending
more time searching for forage of higher nutritional quality. Suckling calves may be at
leisure to be more selective when they graze because a majority of their needs are met via
milk consumption from their mother. Differences in forage harvesting efficiency between
age classes of livestock may also contribute to variable resource selection and use
patterns. For example, younger animals tend to have teeth that are in better condition for
foraging than older animals.
Learned Behavior.
Learned behaviors, both individually and socially, play a large role in livestock
resource selection patterns throughout their lifetime. Animals are sensitive to social
facilitation by different intraspecific classes at various ages and stages of their life.
As a very young animal that is dependent upon mom’s milk and before its rumen is
completely developed, calves tend to be the most influenced by their mother’s
behavior. This effect weakens as calves become yearlings, or “cow-teenagers”,
and peer influences become the strongest. Ultimately, as cattle mature, individual
experiences become the strongest influence of behaviors that dictate foraging and resource
use patterns.
Previous Grazing
Experience. A factor that plays an incredible role in influencing
livestock resource selection and use patterns that should not be considered independently
of age is previous grazing experience. Many studies conducted that have documented
livestock grazing distribution use patterns have attributed portions of their results to
previous grazing experience. Animals that have previously grazed in a pasture or similar
situation are like people who have eaten at a specific restaurant or similar kind of
restaurant previously. They probably know what is good to eat and what is not!
How Can Livestock Behavior Be Modified To Improve
Distribution?
Animal behavior is a reflection of a lifetime of
individually and socially learned behaviors up to that point in the animal’s life.
Therefore, grazing behavior modification to enhance utilization of various plant
communities must be started at a young age and reinforced throughout the animal’s
lifetime to persist, because it’s not easy to teach an old cow, sheep, or goat new
tricks. As animals are the most receptive to learning from their mother at a young age,
shaping young animal behavior to increase their distribution should begin by modifying
mom’s behavior first. An example of this type of modification might be to herd mother
animals away from preferred areas of a pasture, such as areas near a stream, into less
preferred areas, such as upland slopes, influencing the young via their mother’s
actions. Ideally, as generations of animals pass through the herd or flock, these
early-learned behaviors exhibited by maturing animals may become more prominent and
influential to young animals entering the herd or flock.
Cattle have been documented utilizing working spatial
memory to return to places for which preferences have been developed. Preferences
are generally formed for areas that animals perceive as having desirable and adequate
forage. Animals, in general, also respond to various types of punishment and
reinforcement. Perhaps a combination of these factors that influence animal behavior could
be used to improve livestock distribution. An example of this might be to rotate pasture
entrance points (e.g. use different gates) every time livestock are placed in a pasture.
In addition to rotating entrances, managers could provide a source of positive
reinforcement near the entrance and in surrounding areas, such as molasses blocks.
The blocks may cause the animals to create a place preference for that area of the pasture
and influence livestock to return to the area during future use of the pasture.
Additionally, this behavior modification, coupled with the
previous idea of influencing animal behavior at a young age by modifying their mom’s
behavior, by herding animals to areas that generally receive little use, may serve as an
effective and efficient behavior modification and management tool. Herding mother
animals to new areas and rewarding them with something positive may facilitate the
behavior of the animals returning to that area in the future, which may influence future
behavior of young animals that observe their mother’s actions.
Conclusion
Intraspecific grazing of various age classes of livestock
may be an effective tool managers can use to increase livestock distribution at a
landscape level. Understanding the influence of physical, morphological, and physiological
differences among age classes may have on distribution, the relation of each of those
factors to each other, and the advantages and limitations potentially associated with each
is a necessary first step in the development of such tools.
Additional References:
Bailey, D.W., J.E. Gross, E.A. Laca, L.R. Rittenhouse, M.B.
Coughenour, D.M. Swift, and P.L. Sims. 1996. Mechanisms that result in large
herbivore grazing distribution patterns. 49:386-400.
Howery, L.D., F.D. Provenza, R.E. Banner, and C.B. Scott.
1998. Social and environmental factors influence cattle distribution on rangeland. Appl.
Anim. Behav. Sci. 55:231-244.
Pieper, R.D. 1994. Ecological implications of livestock
grazing. p. 177-211. In: M. Vavra, W.A. Laycock, and R.D. Pieper (eds.) Ecological
implications of livestock herbivory in the west. Society for Range Management, Denver, CO.
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