Managing Pasture to Meet Nutrient Needs

Rory Lewandowski, Extension Agent Ag/NR Athens County

Is pasture capable of meeting a beef animal’s nutrient needs? I’ll give a typical extension answer; it depends. It depends upon how the producer manages the pasture, the species mix in the pasture, the class of beef animal in the pasture, and what nutrient needs are targeted. However, in general, with a moderate level of management, pasture should be able to meet the crude protein, energy, and to a large extent, the mineral needs, of most classes of beef animals.

A good place to start in thinking about pasture management is to have some understanding of the nutrient needs of a beef animal. Those needs depend upon such things as body maintenance, environmental conditions, age, reproductive stage and milk production. Generally beef cattle producers pay attention to two main nutrient requirements, energy and protein. Energy needs can be expressed using a term called Total Digestible Nutrients or TDN. Protein needs are expressed using a term called Crude Protein or CP. Using these terms and some common classes of beef livestock that producers most commonly are working with at this point in the pasture season, the nutrient needs are:

Class of Livestock Crude protein TDN
Stockers 12-14 65-70
Growing heifers 10.5 65
Yearling bulls 10.5 65
1200 cow, 20 lb milk 10.7 60
Mature bull 8 50

Now that the producer has some idea of the nutrient needs of a particular class of livestock, the next question is; to what extent can pasture meet these nutrient needs? To help answer that let’s take a look at some book values regarding the nutrient content of pastures:

Pasture type Crude Protein TDN
Tall fescue/Orchardgrass:Vegetative to boot stage 12-16 61-66
Tall fescue/Orchardgrass:Boot to head stage 8-12 56-61
Tall fescue/Orchardgrass:Post head stage 7-8 48-50
Red clover: early flower 14-16 64-67
Red clover: late flower 12-14 59-64

In comparing these two tables a couple of things stick out. First, the crude protein needs of beef animals are not at super high levels. Energy may become a limiting factor in rations before crude protein is short. Second, pasture in the vegetative stage is a feedstuff capable of meeting the nutrient requirements of even the most demanding livestock class, stockers, without additional supplementation. For most cow-calf producers, nutrient needs can be met by keeping pasture in the late vegetative to boot stage. Once seed heads appear, although the crude protein level may still be adequate, it is likely that energy as measured by TDN, will be deficient. Finally, it can be seen that adding a legume to the grass species mix of the pasture can improve pasture nutrient quality.

The beef producer also needs to understand that not only is pasture quality important but also pasture quantity. In other words, the grazing beef animal should be able to get a mouthful of nutritious pasture grass with each bite taken. Research has demonstrated that grass grazed at a 6 to 10 inch height will provide from 1800 to 2500 pounds or more of dry matter forage per acre. When that dry matter availability drops below 1000 to 1200 pounds per acre, somewhere around a 3 to 4 inch pasture height; the animal does not get a mouthful of forage with each bite. At this point, even if nutrient levels are adequate in the pasture plant, the animal will not get enough total intake to meet daily nutrient requirements.

With regard to minerals, on good pasture, calcium, phosphorous and potassium are likely to be supplied in adequate amounts. Early in the grazing season it is important to provide a mineral mix that contains magnesium oxide to reduce the risk of grass tetany. A good salt mix should be provided throughout the season that will meet livestock requirements for trace or micro minerals.

In closing, the beef producer should recognize that pasture is a valuable resource capable of meeting the beef animal’s nutritional needs when the producer exercises some management skills through the use of pasture rotations and good grazing principles.