Cattle nutrition and grazing behavior during short-duration-grazing periods on crested wheatgrass range.

Abstract

Daily changes in diet quality, ingestive behavior, and daily forage intake were investigated using crested wheatgrass [Agropyron desertorum (Fisch.) Schult. and A. cristatum (L.) Gaertn.] range in a 3-year study to provide an understanding of how the rapid defoliation that occurs under the high stocking density of short duration grazing (SDG) affects livestock nutrition. A 10-paddock short duration grazing cell was stocked with yearling Angus heifers. Grazing periods in paddocks varied from 1 to 4 days. Dietary quality was assessed daily within pre-selected paddocks by determining crude protein content and in vitro organic matter digestibility of extrusa samples collected from esophageally fistulated animals. Three variables of ingestive behavior were measured concurrently, including ingestion rate, biting rate, and grazing time. Daily forage intake was estimated by multiplying ingestion rate and grazing time. There were large daily changes in diet quality, ingestive behavior, and forage intake during the grazing period within particular SDG paddocks. Diet quality declined significantly during the 2 or 3 day grazing period in all 3 years. Although not as consistent throughout the study, ingestive behavioral responses changed significantly, indicating declines in forage intake during the grazing period on a particular paddock. Ingestive behavior was correlated with several characteristics of the sward that changed as it was defoliated. Ingestion rate decreased with herbage availability, apparently causing the animals to compensate by increasing biting rate or grazing time. Ingestion rate and biting rate decreased as nutritional quality of the sward declined, as indicated by decreased crude protein content and digestibility, and increased fiber content. Based on the system studied, grazing periods in SDG paddocks should be no more than 2 days to maintain high levels of livestock performance on crested wheatgrass range.