Evaluating rules of thumb for grazing management

Over the years, I’ve heard rangeland managers develop rules of thumb, or short phrases, to try to help them simplify decisions that need to be made to manage their pastures. Some of these rules of thumb have merit and scientific or economic data to support the rules of thumb; however, some rules of thumb may be unfounded and lack informational support.

The following is a list of some common rules of thumb, along with an explanation of whether or not the rule of thumb has any merit or basis of support. Thumbs Up means it’s a rule of thumb with merit, and a Thumbs Down indicates the rule of thumb lacks support and has room for improvement. A Thumbs Up and a Thumbs Down means that arguments may be made for and against the rule of thumb. Below is the first set in a series of three sets of rules of thumb that will be shared in upcoming newsletters.

Take half and leave half. Thumbs Up. This is probably the most common and most important rule of thumb for rangeland managers to follow. Clipping studies and grazing studies have both shown that when approximately 50% of the growing season’s top growth is removed, animal performance and vegetative production are at near optimal levels and performance can be sustained over a long period of time. At the right stocking rate, half of the 50% of growth that is removed during the growing season, or 25% of the total growth for the year, is actually ingested by grazing animals. The other 25% of the total growth that disappears does so as a consequence of trampling, defecation, wildlife use, insect feeding, and natural senescence and weathering of the plant material. The 50% of total growth that should remain standing through the growing season is needed for leaves to continue to photosynthesize to produce carbohydrates for new leaf material, for maintaining and producing new root growth, and for storage during the dormant season to serve as a source of energy to initiate new plant growth the next season. The right stocking rate for a pasture balances forage availability with animal removal to achieve this concept of take half and leave half on a sustainable basis.

You can’t overgraze and make money. Thumbs Up. Pastures that are overgrazed produce lower net returns than pastures that are stocked at a moderate rate using the take half and leave half concept. Greatest net returns per acre will be experienced when collectively the greatest number of animals achieve their most efficient individual gain (Fig. 1).

This is also the stocking rate where total pasture gain on a per acre basis is usually at its greatest point of efficiency. As stocking rate increases further, additional animals cause enough competition for high quality forage, or competition for enough quantity of forage, that individual performance is reduced. This results in production per acre increasing because more animals are on pasture, but production per acre increases at a decreasing rate because each individual animal will gain fewer total pounds.

Increasing stocking rate further and removing more vegetation results in even more competition and lower individual animal gain, and animal gain per acre will eventually even start to decline. Grazing animals at high stocking rates don’t achieve great enough gain to cover their own costs of production, so net returns plummet. Returns per acre and per animal are at their greatest level when total gain is most efficient to cover the costs of production.

Grazing studies have shown that the greatest returns per acre are usually achieved at a moderate stocking rate that takes half and leaves half, and are least with heavy stocking when more than half of the standing forage is annually removed.

If it’s not grass, it’s a weed. Thumbs Down. Animal consumption and preference data do not support this rule of thumb. Cattle prefer grass, but studies show that up to 25% of grazing cattle diets consist of forbs (broadleaf plants) rather than grasses, especially early in the growing season. Many forbs are high in protein and are highly digestible when young and still immature. Forbs can be important for animals to maintain a high quality diet.

Rangelands contain many forbs that are native legumes, which are especially high in protein and benefit animal nutrition. These legumes capture nitrogen from the atmosphere and add it to the soil to help maintain fertility and productivity. One of the most common forbs on Kansas rangelands is western ragweed.

Grazing studies have shown that animals may consume 49% of the ragweed vegetation produced during a growing season. Western ragweed will start to reduce native grass production when approximately 35% to 40% of pasture dry matter consists of ragweed. Ragweed composition in pastures is highly precipitation dependent and will rapidly decline during extended droughts. Some broadleaf plant problems do occur in pasture, especially when noxious weeds are considered, but just because a plant is not a grass does not mean that it is not beneficial to the grazing animal or the pasture ecosystem.

Rotational grazing is better than continuous grazing. Thumbs Up and Thumbs Down. Rotational stocking systems are not automatically better than continuous stocking systems. A stocking system still has to be managed properly to be successful and sustainable. A rotational system that overutilizes forage growth and does not balance the seasonal forage removed with the seasonal forage available is still overgrazed regardless of the rotational system being used. Likewise, a continuous stocking system that doesn’t balance forage produced with forage removed and utilizes more than half the forage growth will be overgrazed.

The majority of grazing research studies show that animal production and pasture vegetation production are actually quite similar when continuous and rotational systems are grazed at the same stocking rate. For pastures that have a history of overuse, both systems can be used to help with pasture improvement.

Three main strategies will help to increase pasture production and shift pasture vegetation to more desirable species over time. First, data shows that significantly lowering stocking rate will increase pasture yield and will improve pasture plant composition, even with continuous stocking. Second, providing a rest period during the growing season allows vegetation to accumulate more leaf material and dry matter and allows plants to replenish their carbohydrate status. Providing a rest period during the growing season is the only way to ensure that all plants will have a period in the growing season without any leaf material being removed. And third, implement a combination of the above two strategies. All three strategies will improve pasture condition over time, but providing a significant rest period during the growing season may help improvement to occur more quickly. Practicing some form of rotational stocking system is often a practical way to implement a rest period across all grazing units.