Cool-Season Mixed Pasture Growth Responses to Winter Grazing Severity and Timing of Initial Spring Grazing.

Initiating grazing early, and grazing stockpiled forage late, are approaches to extending the grazing season in order to minimize costs of winter hay feeding. Impacts of initiating spring grazing at different times on subsequent pasture growth are not well-defined. Understanding the impacts of fall and early spring grazing on annual herbage production could help managers make grazing management decisions. Our objective was to compare total-season herbage production when spring grazing was initiated at early, intermediate, and late dates following moderate and heavy defoliation of stockpiled pastures during fall. Stockpiling of perennial cool-season mixed pasture was initiated in August of 2009 and 2010. Herbage masses at the end of each growing season (October 26-29) were 2670-3470 kg dry matter (DM)/ha. Spring-born beef heifers were allocated to grazing treatments on November 12-18 at daily herbage DM allowances of 0.035 or 0.07 of body weight. New paddocks were assigned every 3-5 days. Round bale haylage was fed during December 21-April 19. In spring, pastures were continuously stocked through May 23, after which heifers were combined and rotated among pastures until early August. Exclosures were established in each pasture treatment on March 19-20 and managed under rotational stocking through June 3. Subdivisions were grazed initially on April 9 (‘early’), April 19 (‘medium’), or April 29 (’late’) for a period of 3-5 days, then again approximately 31 days later. Strips of summer regrowth were mowed for determination of hay mass on June 24 and August 12, after which regrowth accumulated for the remainder of the growing season and was measured on October 20. Total-season herbage utilization ranged from 9682-11,558 kg DM/ha among treatments, and increased with later dates of initiation of spring grazing. Date of initiation of spring grazing may have more impact on subsequent seasonal herbage production than does previous fall grazing severity.