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Overgrazing is an issue of time plants are exposed to grazers, not the number of grazers or amount of defoliation.

Walt Davis 1, Editor

August 17, 2020

4 Min Read
Cattle continuous grazing
Time not numbers: Long exposure of grazers to plants is the thing that damages the best plants and allows unwanted plants to flourish.Alan Newport

Overgrazed is a term frequently used to describe an area where the forage has been degraded by overuse. I would suggest a more accurate and useful description.

I say we should instead use the term overgrazed to refer to a plant that has had green leaf removed before said leaf has produced enough energy to replace itself.

A plant must have green leaf to use sunlight to convert carbon dioxide from the air into sugar (energy). Under continuous exposure to grazing, new and tender forage growth will be grazed and re-grazed, while older, tougher forage is not grazed and accumulates. Sunlight falling on senescent forage or on overgrazed forage is largely wasted.

A simple, and highly effective, way to increase the amount of forage produced, is to use time-controlled grazing management to prevent both conditions. Nature’s recipe is to keep a lot of forage in a green and growing state and provide enough quality recovery time to maintain healthy energy levels. This cannot be done by just reducing animal numbers. The frequency of defoliation must be managed. Grazing animals will always eat the best first. With continuous exposure to grazing, the vegetative sward becomes a mixture of photosynthetically ineffective old plants and low-vigor overgrazed plants.

An overgrazed plant is energy deficient and unable to grow normally. This malady occurs not to areas, but to individual plants. Unlike some academic jargon, this is not just scholastic nitpicking about semantics. From a management standpoint, it is important that we understand why some plants are damaged by overgrazing while others in the same area – sometimes even close relatives – are damaged by underutilization.

Completely ungrazed plants are most common when plants are isolated by distance or terrain factors that limit their use, but also occur by happenstance during periods of abundant growth. A plant, ungrazed for some period, becomes unattractive to animals. Part of the explanation for this lies in what constitutes quality forage to grazing animals. Such quality is determined by several factors:

  • Nutritional quality – digestibility and protein content (strongly influenced by the physiological age of plant), and presence of essential minerals.

  • Anti-quality factors – early lignification, toxic content, spines, burrs, prostrate growth habit.

  • Education – animals learn from other animals what plants to choose, and young animals are attracted to plants their mothers consumed while pregnant.

  • Need for variety – all plants contain anti-quality factors to prevent animals from consuming too much of their foliage at one time. The ill effects of some of these factors can be reduced by anti-quality factors contained in other types of forage. No one forage contains everything needed or desired by animals. Having a variety of forages will increase consumption.

  • Fouling with dung and urine, which makes the plant undesirable.

A prime factor in grazing management is increasing forage intake by removing or offsetting as many intake-limiting factors as is feasible. Nature shows us how to do this with the interactions between grazing animals and their predators. The prey animals common to open grasslands. Bison, antelope, wild equines, wapiti – form herds for protection from predators. These herds, through strength in numbers, make it harder for predators to isolate and kill prey animals. A large part of successful kills target animals with disabilities: Old, very young, sick or injured. Herding behavior cannot prevent all predation, but it limits the number of kills by forcing predators to pay a price, possibly injury or death, to subdue a victim.

Congregating in large numbers means that herd animals must move – quite often when feed is limited, less often when feed is plentiful but seldom remaining in one place for long periods. This movement of concentrated animals benefits forage, soil, and soil life. Periods of no grazing allow forage recovery, halt overgrazing (unless animals return too soon), improve nutrition for plants and microbes from large quantities of dung and urine deposited in a short time period, re-incorporate senescent forage into the soil-plant-animal complex, and increase capture of solar energy.

Animals benefit from movement as well. They receive fresh forage regularly, move away from parasites and disease organisms, and create more uniformity of physiological age of diet, which improves function of rumen microbes.

Nature has used the technique for eons: A large number of grazing animals on a small area for a short period of time, followed by a period of no grazing. The same results can be obtained using fencing or herding and can be extremely beneficial in improving profitability, regenerating natural resources, and reducing parasites, predation and disease.

Unless your idea of fun is popping brush behind a bunch of wild cows, it can make ranching enjoyable. You can find more of my ramblings at

The opinions of this author are not necessarily those of Beef Producer or Farm Progress.

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