Graduate Thesis Or Dissertation
 

The influence of grazing systems on the performance and diet of yearling cattle

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  • Research was conducted at the Starkey Experimental Forest and Range in northeastern Oregon to determine cattle performance, diet quality, botanical composition of forage ingested, and production and utilization among rest-rotation, season-long, and deferred rotation grazing systems. The grazing season lasted from June 20 to October 10 of each year. Cows equipped with esophageal fistulas were used to evaluate diet quality and diet botanical composition. Yearling heifers were used to evaluate livestock performance. The weight estimate method combined with a double sampling technique was used to estimate forage production. Utilization estimates were made by employing the use of the ocular-estimate-by-average-of- plants method. Grass was the most important forage class in cattle diets among the three systems. Grasses made up 67.7 percent of cattle diets on the season-long and rest-rotation grazing systems when data were pooled across systems, periods, and years. Forbs and shrubs contributed 19.7 percent and 11.6 percent of the diet, respectively. Area collected and vegetation structure appear to influence the percent by weight of important species found in the diets of cattle among the systems. More grasses were consumed in the season-long system during early summer of 1979 than in the rest-rotation grazing system. Forb consumption decreased from 32.0 percent by weight to 8.1 percent as the grazing season advanced. Shrub consumption totalled only 13.4 and 17.5 percent during early summer and late summer, respectively. Crude protein, acid detergent fiber, lignin, and cellulose values of diet samples were not significantly different among the systems when data were pooled across years and periods. Although values for in vitro dry matter digestibility were different among the three systems, differences were not great enough to change animal performance. Livestock performance data trends were very consistent with diet quality data trends. However, livestock performance was significantly different among the grazing systems when data were pooled across years and periods even though there was little difference in diet quality among the systems. Average daily gains were 0.51, 0.61 and 0.65 kg for the rest-rotation, season-long, and deferred rotation grazing systems. Animals gained significantly more in deferred rotation than in the other two systems. Cattle gained significantly less in rest-rotation than cattle in season-long when data were pooled over years and periods. When spring rainfall was highest in 1980, production was greatest. Utilization was heaviest in the rest-rotation pasture when grazing pressure was heaviest due to animals remaining in this pasture throughout the grazing season. However, utilization totalled only 30 percent during 1980 in rest-rotation.
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