Intake is daily forage requirement expressed as percent of bodyweight or pounds of forage per pound of animal live weight. The range is typically from about 2% for maintenance up to 4% for first calf heifers in low body condition. Length of the grazing season is how many days that pasture is expected to feed the herd.
Using reasonable estimates in the formula, tempered with good judgment, can give a fairly accurate estimate of the pounds of animal live weight each acre can be expected to support. The importance of stocking rate is further illustrated in the next section on managing forage intake.
A very basic objective of grazing management is to ensure grazing animals receive adequate nutrient intake to achieve the performance targets we set for them.
Whether we are talking about lactating dairy cows, growing beef stockers, or finishing lambs on pasture, a given level of performance requires a given level of energy, protein, and other nutrients. Just because the stock are standing in a pretty, green pasture does not necessarily mean those needs are being met. To achieve a target production level, a defined quantity of calories must be consumed. For example, a 700-pound heifer with a 1.75 lb/day target rate of gain would require approximately
12.4 Mcal/day. If she consumes less than that amount, she will not reach her target weight on time. Her energy intake is controlled by the combination of weight of dry matter forage consumed and the energy density of that forage. Our challenge as grazing managers is to ensure we provide her the opportunity to reach our performance target.
Voluntary forage intake (VFI) by grazing animals is controlled by three factors: time spent grazing, biting rate, and bite size. The first two are largely beyond our control. Ruminants divide their days into three activities with roughly the same amount of time spent grazing, ruminating, and resting. With excellent forage conditions, any class of ruminant can meet its physiological needs in as little as four