No description available.

No description available.

A trial was conducted May 1 to September 4, 1989 at the Eastern Oregon Agricultural Research Center (EOARC) Burns, OR to examine the effects of strip or continuous grazing management on the diet and performance of steers grazing native flood meadows. The objective was to determine if strip grazing would be a more efficient means of grazing management than continuous grazing. The experiment was designed to test diet quality, botanical composition of the diet, daily dry matter (DM) intake and performance of yearling steers. Eighty yearling steers weighing 253±17 kg were selected from cattle at the Squaw Butte Experiment Station. The experimental design was a randomized complete block, with blocking based on past forage production. Treatments were continuous or strip grazing. A representative meadow of approximately 22.4 ha was divided into four equal pastures. Continuous grazing steers had access to 5.6 ha pastures for the duration of the study. Animals on strip grazing were confined to an area that was estimated to provide 5-7 days of forage using New Zealand portable electric fencing. Strip sizes were predetermined based on standing forage crop. Steers were not allowed to graze more than 7 days in any one strip. Diet quality was estimated from bi-weekly esophageal samples. Extrusa was collected from 4 esophageal fistulated steers per treatment on two consecutive days. Collections were timed to coincide with the mid point of the strip being currently grazed. Samples were pooled by collection dates and analyzed for CP and IVOMD. Dietary OM intake was estimated from biweekly, 24 hr total fecal collections starting the day following esophageal collections. Total DM fecal output from 6 fecal collection steers per treatment was corrected with the %IVOMD to predict actual DM intake. Diet botanical composition was estimated by microhistological examination of fecal sub-samples. Animal weight gains were recorded bi-weekly. Experimental animals grazed together at all times during the trial. Initial stocking densities were 2.0 AU/ha in each treatment pasture. Steers were counted as .56 AU with 20 steers grazing 5.6 ha pastures. The average strip size over the trial was .46 ha; and depending upon standing crop of forage, ranged from .23-1.15 ha. Record moisture from snowmelt and rainfall resulted in greater than expected standing crop of forage. This growth resulted in under stocking of both treatment pastures. A 1.08 ha block was removed as hay from the higher forage producing strip treatment block to adjust for over abundant forage. This resulted in a total mean strip grazed area of 4.37 ha or 22% less than continuous grazing. Actual grazing density means over the summer were 2.6 AU/ha for continuous and 3.15 AU/ha for the strip treatment. Available forage was determined from clipped plots on a DM basis and expressed as herbage allowance at a given point in time. Herbage allowance for steers in continuous grazed pastures ranged from 405-1153 kg/AU when measured at bi-weekly intervals and 68-186 kg/AU for strip grazed steers when estimated at the beginning of each strip. Grazing pressure was higher for strip grazed steers (.10 AU/kg) compared to continuous (.02 AU/kg). Diet quality declined significantly over the summer (P<.01). Analysis for CP in steer diets provided values of 13.9 vs 10.9% for continuous and strip treatments, respectively. However, this difference was not significant (P=.14). Digestibility analysis suggested that forage in continuous diets tended (P=.07) to have higher IVOMD than strip diets (64.6 vs 60.7%), respectively. Daily herbage intake was similar (P=.42) for both treatments when expressed as a percentage of body weight. Diet botanical composition was positively affected by the type of management system. The amount of the major grass species, meadow foxtail (Alopecurus pratensjs), was increased (P=.05) 39% in the diet of strip grazing steers. Differences were noted in the amounts of other, less frequently occurring grass species. The total amount of grass tended (P=.06) to be higher in strip diets (49% vs 35% for continuous). Rushes (Juncus spp.) and sedges (Carex spp.) contributed a similar percentage to the diets of both treatments. Forbs comprised less than .5% of the overall diet of both strip and continuous steers. Individual animal performance tended (P=.09) to be higher under continuous grazing management. The ADG was 1.16 and .77 kg for steers in continuous and strip grazing, respectively. However, total animal production per hectare grazed area (26.14 vs 22.13 kg/hd) was not considered different (P=.17). / Graduation date: 1991

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 56-61). Also available on the World Wide Web.

Thesis (Ph. D.) -- Lincoln University, 2009. / Also available via the World Wide Web.

Inaug.-diss.--Giessen. / Lebenslauf. "Literaturverzeichnis": p. 86.

No description available.

No description available.

Estuarine phytoplankton growth is often controlled by nitrogen availability. In addition to overall nitrogen loads, nitrogen form (organic vs. inorganic) is an important factor affecting estuarine phytoplankton growth and community composition. Recent studies have shown that in addition to nitrogen availability, trophic cascades and relaxation of grazing pressure may also be important for phytoplankton bloom formation in estuaries. With a goal of better understanding how nitrogen availability and grazing pressure interact to control estuarine phytoplankton growth and community composition, we examined the individualistic as well as the combined effects of nitrogen (varying availability and form) and grazing pressure on estuarine phytoplankton growth and community composition in the Neuse River Estuary, North Carolina, USA. During each of three sampling events (June 2011, August 2011, March 2012) natural phytoplankton assemblages were manipulated with added nitrogen (as urea or nitrate) and reduced grazing pressure (by filtering out zooplankton grazers). Treatments were incubated for 48 hours in an experimental pond, and subsamples taken daily to assess phytoplankton growth responses to treatments through chlorophyll a, diagnostic photopigments and cell enumerations. The effects of nitrogen additions and reduced grazing pressure varied throughout the events. In June, only nitrogen addition stimulated phytoplankton community growth (chlorophyll a), while in August, only grazing reduction had a significant impact on community growth. Neither treatment had a significant effect on community growth in March, as the phytoplankton community faced phosphorus-limitation and decreased grazing pressure associated with cooler winter/spring temperatures. While both treatments did not continuously effect overall phytoplankton growth throughout all experiments, there were always effects seen in some diagnostic photopigments, indicating varying taxa-specific responses to treatments throughout the year, which can be explained by shifts in phytoplankton community composition and environmental factors. These results demonstrate the importance of both bottom-up (nutrient availability and form) and top-down (grazing) controls in a temperate, eutrophic estuary. Results also hint at the potential for other factors (i.e. light and phosphorus-limitation) to play a role in phytoplankton growth as well. Phytoplankton growth, biomass and community dynamics are relevant indicators of environmental change and this study highlights the need to consider the potential interactive effects of controlling factors for proper management of estuarine ecosystems.

Re-introducing heterogeneity to native North American rangelands is imperative to maintaining grassland biodiversity, and it has been suggested that using a variety of cattle grazing intensities on the landscape could accomplish this. I used generalized linear mixed models to describe the effects of grazing intensity on vegetation structure, plant species diversity and plant communities over four years. I used the Mantel test and non-metric multidimensional scaling to illustrate changes in plant communities with varying grazing intensities and over time. Effects of grazing were cumulative and changed over time, upland and lowland habitats responded differently to grazing intensity, and heterogeneity was maximized at the landscape scale under a variety of grazing intensities. When conservation is the primary goal, a variety of grazing intensities on the landscape can be used to increase heterogeneity, and therefore grassland biodiversity.