Grazing is the base of the nutritional program for most cattle producers. It's a base, however, that changes every year due to climatic conditions, last year's management, types of forages, weed infestation, grazing intensity and other factors.
During periods of initial growth in the spring and summer, most forages are high in nutrient content and moisture. As plant growth advances, the nutritional differences in forage types become more evident.
The nutrient evaluation of range forage can be based on their amount of protein, energy, phosphorus and vitamin A. These are the limiting factors of rangeland forages. These forages may be divided into three common classes: forbs (broad-leaved), herbaceous plants (grasses but may be weeds) and shrubs.
Grasses rapidly decline in digestible protein as they mature. As grass matures, it moves nitrogen from its above-ground parts — which are available to the grazing animal — to storage below the ground.
Shrubs, on the other hand, are good sources of protein even after they reach full maturity. This is because nutrients remain in branches and leaves as well as in the roots.
Generally, forbs are intermediate between shrubs and grasses with respect to protein content during most seasons.
Phosphorus is often limiting in range forage plants. Grasses are low in phosphorus soon after they form seed, while shrubs are generally considered good sources of phosphorus even when mature. Most forbs have a phosphorus content only slightly lower than that of shrubs.
Digestibility is the proportion of a dietary nutrient available for animal metabolism and directly influences intake. As digestibility goes down, intake goes down.
Shrubs are not a good source of energy after they reach maturity or set seeds. Forbs, however, are intermediate between grasses and shrubs in furnishing energy.
Generally, energy is more frequently the limiting factor in grazing than protein is. However, the biggest problem, especially when plants are mature, is getting enough dry matter (total nutrients) into the animal each day.
Other factors may also influence the nutritive value of range plants. Range condition, for example, can alter total forage intake of grazing cattle. Research shows protein and phosphorus content are about the same in plants growing on good versus poor range condition.
However, plant species on poor-condition range may be less digestible than plant species on good-condition range. This may reduce total forage intake by livestock — the animal either can't or won't eat enough forage.
Management factors such as stocking rate and specialized grazing systems also can influence grazing animal nutrition. Heavy stocking rates will reduce individual animal performance and may result in damage to the forages.
Carefully planned grazing can increase diet quality. In grazing cells, the longer animals stay in a particular area, the further diet quality is reduced. If grazing periods are shortened, be sure to consider the implications of the corresponding rest periods.
The old grazing adage of “take half and leave half” is true. When up to 50% of the leaf volume of a plant is removed, root growth stoppage is about 2-4%. This level would have little effect on plant regrowth.
But, if 60% of the leaf volume is removed, root stoppage growth escalates to about 50%. At 80% removal, the roots have no regrowth. That delays regrowth of the upper parts of the plants and may increase plant death and winterkill. This is especially critical in drought areas and will affect next year's plant growth.
In any grazing situation, a common goal is to obtain even grazing distribution throughout the pasture. This may be difficult due to various types of forage — cool-season versus warm season species, different soil types, differences in terrain, weed infestation, stage of maturity and water, salt and supplement distribution.
Class of livestock also plays an important role in efficient utilization of forages. Information from the U.S. Forest Service includes the following observations:
Yearling cattle utilize pastures more uniformly over variable terrain than cows with calves.
Yearling heifers will utilize steep, rocky terrain more evenly than yearling steers.
Cow/calf pairs utilize forage near water more heavily than yearlings.
Older cows with calves tend to use sheltered areas most often using open terrain only when needed.
Young cows with calves tend to use open grasslands rather than sheltered areas.
These observations may not apply to all range situations or breeds of livestock.
Proper grazing techniques are becoming more critical in the profitability of any cattle operation. Reducing feed costs while maintaining production and range viability is a balancing act. With proper management and knowledge, producers can improve pastures and profitability.
David Wieland is a nutrition consultant specializing in cow/calf, feedlot and horses. Based in Shepherd, MT, he also publishes a subscription newsletter. Contact him at 406/373-5512 or e-mail firstname.lastname@example.org.