The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Thursday, January 31, 2008 - 10:20 AM
Matching Plant and Animal Processes to Alter Nutrient Supply and Performance of Strip-Grazed Beef Cattle
P. Gregorini, Pasture Systems & Watershed Management Research Unit, USDA-ARS, Building 3702 Curtin Road, University Park, PA 16802
The outcome of any grazing strategy results from the interactions among herbage ingestion and digestion. Herbage chemical composition fluctuates during the day and therefore nutrients supplied by pasture. Such fluctuation is mainly attributable to photosythate accumulation, which increases herbage nutritive value from dawn to dusk. While grazing cattle seem to follow this temporal variation by increasing intake rate at dusk, this phenomenon is not yet maximized. Changes in timing of herbage allocation (late in the afternoon instead of early in the morning) alter duration and intensity of individual grazing bouts, modifying the connection among them into the temporal distribution. Dusk grazing bouts become longer and more intensive when the herbage has the greatest nutritive value. This change in the grazing pattern modifies the dynamics of ruminal metabolism, increasing glucogenic and aminogenic nutrient supply, which leads to better performance of beef cattle. Because hunger is related to herbage intake rate, the positive effect of afternoon herbage allocations could be enhanced by strategic fasting periods. Prior to afternoon herbage allocations, short fasting periods generate even longer and more intense grazing bouts at dusk, which at the same level of daily herbage intake may increase nutrient ingestion, but not digestion nor nutrient supply, explaining the null effect on performance of beef cattle under this management. Despite this lack of positive effect in cattle performance, matching afternoon herbage allocations with prior short fasting periods may allow graziers to graze cattle in shorter grazing sessions, reducing treading, trampling and fouling, and potentially improve herbage production. It was believed that producers have partial control over herbage quality, nutrient availability and the grazing process. However, even at the same amount of resource allocation, a simple matching of plant and animal processes may help graziers to gain control and allocate nutrients supplied by pasture with greater efficiency.