County agent Lloyd Culter, Lake Co. Indiana needed an explanation for the failure of a well designed rotational grazing system of dairy cattle. The dairy farmer subdivided his bromegrass-Ladino clover pasture into 7 paddocks with the plan to graze each paddock intensively prior to moving the livestock to an adjacent paddock. By late June the dairyman was in serious trouble. His grazing pattern and unfortunate consequences are described below.
At the onset of grazing, the bromegrass in the first paddock was approaching the transition stage of development. Leaf sheath elongation had raised the collar zones of most of the leaves to a vulnerable height such that the leaves were severed beneath this meristematic zone. However, internode elongation had not yet elevated the shoot growing point, thus this important meristem system remained as part of the stubble. As a consequence, the flowering culm continued to grow, ultimately producing a seed stalk with very few leaves. British scientists use the term "denuding" to describe this effect. The culms are indeed naked, only the flag leaf remained on many of the culms.
Denuded paddocks should be clipped by the time seed heads emerge from the boot because the developing seed head takes precedence over vegetative renewal by means of new tillers from crown tissue. This was clearly demonstrated in paddock 1. New tiller initials were formed, but shoots did not emerge; a manifestation of apical dominance.
The bromegrass in the second paddock was "decapitated." Decapitation implies that culm development was sufficiently advanced to raise the growing point of the shoot to a vulnerable position. The entire above-ground meristem system was destroyed. In this instance, grass recovery was slow due to the weak development of basal buds in crown tissue. When visited in late June, the available forage was comprised chiefly of clover and weeds. The dairyman was reluctant to use this paddock on the subsequent grazing cycle due to the associated bloat hazard.
Bromegrass in the 3rd paddock had approached the boot stage of maturity when offered to the livestock. The grass was as yet quite palatable: cows consumed the available forage in good fashion. Grass recovery was totally dependent of production of new shoots from basal buds in crown tissue which, by the boot stage, are normally capable of providing competitive regrowth (see Defoliation section).
The 4th paddock was grazed initially when bromegrass seed heads had started to appear. By this stage the grass was stemmy and unpalatable, consequently the cattle refused the forage. Milk production dropped sharply. In desperation, the manager moved the cattle to the 5th paddock where the grass was even less fit for grazing. He called the County Extension Agent for help. A grass physiologist familiar with developmental stages was invited to come along. The dairy farmer asked, "Where should I put my cows? I have nothing but poor choices." The first two paddocks were predominantly clover and weeds, presenting bloat hazards; the third paddock was hardly ready for further grazing. He readily admitted that the remaining ungrazed paddocks should have been harvested for hay two weeks prior to this late-June visit.
What went wrong? The long-standing rule of thumb: "take half and leave half" would have ensured that the cattle moved across all of the paddocks before the initial growth became unpalatable. This would have avoided untimely "denuding" and "decapitation" in the first two paddocks. The remaining paddocks would have been "decapitated" in a timely manner. Furthermore, timely seed head removal would have triggered early production of aftermath shoots from crown tissue prior to the onset of arid conditions.