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

      Olson, K. C.; Rouse, G. B.; Malechek, J. C. (Society for Range Management, 1989-03-01)
      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.
    • Some effects of a rotational grazing treatment on cattle preference for plant communities

      Walker, J. W.; Heitschmidt, R. K.; Dowhower, S. L. (Society for Range Management, 1989-03-01)
      Rotational grazing is commonly assumed to improve livestock distribution compared to continuous grazing, but little evidence supports this contention. Research was conducted on the effects of rotational grazing (RG) compared to continuous grazing (CG) on the preference of cattle for plant communities. Different livestock densities in the RG treatments were created by varying the size of paddocks in a 465-ha, 16-paddock, cell designed RG treatment stocked at a rate of 3.6 ha/cow/yr. Paddock sizes of 30 and 10-ha were used to simulate RG with 14 (RG-14) and 42-paddocks (RG-42), respectively. The CG treatment consisted of a 248-ha pasture stocked at 5.9 ha/cow/yr. Data consisted of hourly daylight observations of cattle location and activity during 8 seasonal trials lasting 6-15 days. These data were expressed as a percent of the time cattle were observed in each of 4 plant communities and the area surrounding permanent water. Relative electivity (RE), a preference index, and a selectivity index (SI) that measures departures from random distribution were calculated from these data. Relative electivity (i.e., preference) for plant communities was not affected by grazing treatment. However, cattle were less selective for plant communities as livestock density decreased from the RG-42 to the CG treatment. In the RG-14 treatment, the cattle were either unaffected or less selective on the last day than on the first day in a paddock. We hypothesize that grazing systems influence cattle preference for plant communities by affecting the availability of forage biomass per unit land area rather than by their effect on grazing pressure.