Grazing systems must be designed with both plant growth and animal performance in mind. Optimizing the balance between available forage and stocking rate helps to ensure profits by maximizing animal performance while safeguarding pasture productivity.
As a grass plant approaches maturity (seed heads appear) it is tolerant of defoliation, as under hay or silage management. However, under a grazing system, whether with continuous or rotational, the pasture must be utilized long before the grasses in question approach the heading stage. Grazing systems are needed that permit immature shoots to be defoliated with minimal risk of delayed regrowth. If improper management causes delayed recovery, undesireable invasive species will soon appear.
This educational module is designed to provide a better understanding of regrowth mechanisms of grasses so that they can be grazed with minimal risk of delayed recovery following defoliation. These management guidelines will enable the livestock manager to maximize stocking rates while maintaining optimal plant production, thereby improving efficiency.
Optimum grazing efficiency exploits the inherent capacity of grasses (and legumes) to recover following defoliation, providing additional forage for later consumption. This is the goal in pasture management. Livestock are selective in their grazing habits. Thus, with continuous grazing or ill-conceived sequential grazing schemes, it is common to find that certain species reach maturity and become unpalatable, while other species in the mixture are grazed prior to the time they have achieved grazing readiness. Mismanagement of the desired grass(es) results in dynamic changes in sward composition; disappearance of desired types and the appearance of undesireable types.
To achieve optimum efficiency, pastures should be grazed at a time, and in a manner, which ensures prompt competitive regrowth. To achieve this goal, the manager must understand the growth mechanisms which account for grass recovery, and be able to identify the growing points (also called the meristematic zones) which will provide either for continued leaf blade growth or for new shoot production from the alternative regrowth mechanism found in the crown (base) of the plant.
When given unlimited access to grazing lands, livestock will select what is most palatable and most easily accessible. This would appear to be an ideal system. The North American Bison enjoyed this luxury. When grass produced seed heads and became unpalatable, the Bison grazed the recovery growth in areas previously visited. Simply stated, this is grazing without design; by default.
An alternative is to graze by design; i.e. develop a system of controlled grazing. Research has demonstrated that more animal product can be produced per unit area of land when forage utilization is not left to chance, but is scheduled to take advantage of the grass plant's ability to produce multiple harvests; to grow and recover providing for increased carrying capacity.
Previous Problems with Rotational Grazing Systems
Many rotational grazing systems have failed to yield expected results because defoliation schedules were not based on scientific principles. Livestock were shifted between paddocks in an arbitrary manner or according to an ill-conceived rotation schedule (i.e. a preset time period without regard to developmental stage). In some instances livestock were offered forage that was mature and unpalatable. As a result, animal performance dwindled. In other cases, the grass was defoliated in a manner that rendered it incapable of prompt regrowth. Weeds flourished and pasture productivity suffered. Carrying capacity during mid-summer diminished.
What we propose, in contrast, is to develop defoliation management schemes based on sound scientific principles outlined in this educational module.
The purpose of this project is to convey information essential for the development of these management skills.