In part I of this grazing primer we covered some names and principles for managed grazing, as well as stocking rate and stock density. Today we’ll continue along those lines with more terms and definitions.
Recovery time – This is the amount of time allowed by the grazing manager for plants to regrow after a grazing event. It is sometimes erroneously called “rest,” but this term doesn’t remind the grazing manager that plants actually need time to regrow adequate leaf material for photosynthesis and fully recharge the energy stored in crowns, rebuild root systems, and reconnect with underground life such as bacterial and mycorrhizal fungi. This is even more important than once understood, since plants trade carbohydrates with underground life for nutrients they may not be able to mine from the soil with their own root systems. Allowing plants to fully recover builds soil life and fertility, thereby increasing productivity. The most productive pasture plants also require the longest recovery time to thrive.
Graze period – This is vital information for grazing managers because the true definition of overgrazing, from the standpoint of plants, is being grazed or bitten off a second time or more before it can recover from the first grazing. This means grazing several times over several days is very damaging to individual plants, although repeated biting over a day or a few hours is not problematic.
Graze period also is inversely related to the number of paddocks used in a grazing operation. The higher the number of paddocks, the shorter the graze period.
AUDs, ADAs or cow days per acre – These are primarily measurements of the productivity of your resource. These measurements are a good way to track progress or regression over time, and is very important to help with grazing planning and management. This is very important to good managers who should be changing grazing patterns and herd makeup from year to year and season to season.
Animal Unit Days is based on an Animal Unit (AU), which the NRCS generally says is one mature cow of about 1,000 pounds and a calf as old as six months, or their equivalent. NRCS uses 30 pounds of air-dry forage per day as the standard forage demand for that animal unit. Animal Days per Acre is generally simpler in that the manager can choose his size of animal and simply track how many days and the number of animals were in a paddock. Cow days per acre is a variation of ADAs, based on a manager’s particular cow size.
As an example how to use this, a herd of 100 dry cows weighing 1,400 pounds (140 AU equivalent) might stay in a one-acre paddock one day, producing 140 ADAs for that grazing. Two of the same grazings would produce 280 ADAs for the year. This tells the manager if rainfall and time of recovery and time of year are similar, that paddock should allow a herd of 233 600-pound steers should be able to graze one day on the same paddock (140ADA / .6 = 233).
This comparison can be weight-adjusted most simply, or more accurately adjusted by the consumption of a class of livestock and forage type. It should also be adjusted to include calves with cows according to their average weight.
Residual forage — This is the forage left behind, usually expressed as a percentage of the forage present when cattle entered the paddock. Many managers aim to leave 50% under many circumstances. If forage is ample and animal production is more desired, leaving behind a higher percentage, such as 60-75% might be the goal, leaving a residual of 25-40%. If rationing out winter forage along with protein supplement, a consumption level of perhaps 80% with only 20% residual might be the goal.
Tomorrow we’ll publish Part III.