Considerations Necessary for Winter Nutrition on Rangelands
By Derek Scasta, Extension Rangeland Specialist
As we enter the month of October, the cooler temperatures and higher probability of snow should get us thinking about livestock nutrition for the upcoming winter months.
As most grasses are dormant now, or are rapidly going dormant, they have much lower quality than they did in the spring and summer when they were actively growing and conducting photosynthesis. This relationship reflects the old adage that “maturity is the enemy of quality,” or in other words, as a plant gets older, its quality decreases. Quality in the context of livestock nutrition and rangeland forage can mean either crude protein, which is related to nitrogen content, or digestibility, which is related to fiber and lignin content.
During this phase of plant growth, plants redistribute nutrients from the leaves to the root system, ultimately reducing nutrient quality available to livestock. As plants mature, the cell walls increase in thickness and fiber content – changes that reduce the digestibility of the plant material. This relationship can also depend on the plant species and elevation of the winter pastures as it can be different for cool-season plants, such as western wheatgrass, versus warm-season plants, such as blue grama.
The availability of forage on rangeland and its relative quality and quantity is important to put in the context of the class and species of livestock you are concerned about. For cattle, general rules of thumb are: dry cows need about seven percent crude protein, growing heifers need about 10 percent crude protein, and lactating cows need about 12 percent crude protein.
Furthermore, it is important to be aware of certain animal life stages that are stressful nutritionally. For cattle, these stressful periods are times when the animal has a high nutritional demand, particularly late gestation and early lactation. Thus, you have to consider your reproductive management and calving/lambing periods relative to forage quality and animal demand.
The relative amount of forage available is also a reflection of energy available to livestock. Because energy is derived from adequate dry matter intake, if grass is available in adequate amounts, energy will typically not be the limiting nutritional consideration for livestock on rangeland.
Subsequently, a producer could supplement only with protein to enhance the digestibility of the adequately available dormant forage. In essence, this provides a supplemental source of nitrogen to stimulate the microbial bacteria in the rumen that digest the forage. This will increase the digestion rate and rate of passage. However, if the relative amount of rangeland forage was not adequate, then the supplementation program must provide adequate sources of energy with harvested forage. Producers must be able to put all of the above information together and determine if supplementation should be based on energy or protein.
However, this cannot be determined by assessing forage availability alone because animal body condition also matters. If animal body condition is thin, energy is a concern because animals need to gain weight. This becomes an issue often for producers who are overstocked and have cows that are thin. In this case, producers should consider supplementing with high energy and low protein supplements.
In contrast, let’s say a producer is feeding a group of late gestating beef cows that are on dormant winter range. These cows are in acceptable body condition and abundant grass is available. However, the grass is low in nutrient content and these animals are in a stressful period where their nutritional needs are high. In this scenario, crude protein is the primary limitation and should be the focus on the winter nutrition program for these particularly cows. This will enhance microbial requirements and digestibility of rangeland forage and increase dry matter intake.
In summary, if you need to get started planning your winter livestock feeding program you have to address the following issues to build the proper nutritional program: first, understand how rangeland forage decreases in crude protein and digestibility as it matures; second, understand animal nutrition demands relative to the different classes of livestock and gestation/lactation stages; and third, identify the limiting constraint of protein and energy by assessing forage availability and animal body condition.
As you are all well aware, one of the greatest issues in the livestock industry is appropriate and economical supplementation in the winter. Hopefully, this article has stimulated some more thoughts about how you are approaching the upcoming winter and how you might better balance the available rangeland forage with your livestock’s nutritional needs.