Grazing vs Mowing
Herbivores harvest their foods through a fairly mechanical process that is not unlike the cutting of a field of hay with a mower. The amount of hay cut with a mower is a function of mower speed X mower width X the amount of time the mower is spent in operation. Dry matter intake in an herbivore is a function of bite rate X bite size X the amount of time the animal spends grazing. And although the processes are very similar, there is one big difference between a mower mowing and an herbivore foraging.
A cutter bar on a mower is nonselective. It does not care what a plant looks like, smells like, feels like, tastes like, or whether or not a plant is nutrient dense or loaded with toxins, tall and rank, or short and sparse. Herbivores do care. And when animals have concerns about what they are eating, they do not eat, or if they do eat, their intake is limited.
As examples, when grazing animals are placed in environments where plant densities and thus yields are low, they have a difficult time consuming enough forage to meet their requirements. The same can be said for pastures that have been grazed to extremely short residual forage heights. Low yielding, sparse pastures tend to result in animals taking in smaller amounts of food with each bite and they also reduce the number of bites taken per unit of time. To compensate for this, herbivores have to increase the amount of time they spend foraging, and in the process they waste energy covering more ground. Unfortunately, this is a classic example of the law of least effort. The animals work harder and longer but get less for their efforts.
A very similar problem exists when herbivores are placed in environments where the plants are tall and rank. While having something to eat is generally better than having nothing to eat, again, studies have shown that most herbivores, most of the time, prefer green leaf.
Just as the amount of hay cut in a day is reduced by slower versus faster mower speeds, narrow versus wider mower widths, or less versus more time spent mowing, so too is the amount of dry matter ingested by an herbivore by anything that negatively impacts bite rate, bite size, or the amount of time spent foraging.
Your Job: Make the Most of Your Stock’s Time
Here’s where you come in. Making it easy for your animals to harvest their own foods with the least amount of effort and in the shortest time possible is the key to high animal performance.
In order to prevent the “Law of Least Effort” from robbing you of profits, you need to ensure that your livestock are actually grazing on fairly decent land and not on some misnamed piece of real estate that you are simply calling pasture. In other words, avoid the swamp, avoid the ski slope, and avoid low fertility or marginally productive lands.
Providing 2 or 3 acres of low- quality land where plant densities and yields are low is not a substitute for 1 acre of high-quality land where plant densities and yields are higher. When plant density and yields are low, herbivores have to forage longer and cover more ground to find enough to eat.
Generally speaking, a good pasture is a pasture where animals can easily harvest their own feeds with a minimum amount of effort. A good pasture needs to be on good land, not the poorest land on the farm or ranch. A good pasture will have an adequate kind, amount and quality of feed available to meet the nutritional requirements of your particular kind, number and class of livestock. And a really good pasture will be utilized with a high level of land management including, when required, soil fertility amendments, brush control, water management, and reseeding to ensure a diversity of plant species.