Twenty four Awassi lambs (mean BW 24.4 kg) were used in a two periods experiment to measure maintenance (zero growth) and growth requirements of metabolizable energy (ME). During the pre-treatment period (period 1, 3 weeks) all lambs were maintained at a constant level of feed intake (2% BW). During the treatment period (period 2, 10 weeks) the lambs were divided into four equal groups and fed different amounts (2, 3, 4 and 5% of BW). Six additional lambs of similar BW and age were killed at the beginning of the experiment to compare final empty body weight (FEBW) with initial body weight (IBW). Twelve lambs, divided into four equal groups were fed the experimental diet in the same amounts as in the growth experiment (period 2) to determine the digestibility of energy.
Energy requirement for maintenance (EM) was measured by both constant weight technique, using data collected during period 1, and regression technique by regressing ME intake on body weight gain (BWG) and empty body weight gain (EBWG). EM measured during the constant weight period (pre-treatment) and overall experimental period (pre-treatment plus treatment periods) were 0.482 and 0.466 MJ of ME per kg M0.75 per day. Predicted energy requirements for growth (Eg) calculated from equations derived during the treatment period were 0.433, 0.623, 0.782, 0.910 and 1.007 (MJ per kg M0.75 per day) for the growth rates 50, 100, 150, 200, and 250 (g per day) respectively. It is concluded to be more appropriate to use the values derived during the overall experimental period for maintenance and the overall treatment period for growth as they are most applicable to production situations. 相似文献
This article presents a modeling framework that enhances our ability to analyze the implications of policy for future sustainability of industrial systems. The framework quantifies the relationship between physical input and waste flows, capital vintage, and investment behavior in the U.S. pulp and paper industry. A regional vintage model is developed that simultaneously incorporates investment decisions, vintage structure of the capital stock, and physical material and energy flows, in addition to paper demand. Each capital vintage is specified by size, output structure, and age-specific retirement rates, as well as fiber use and energy intensities. Both embodied and disembodied technological change are incorporated, as well as greenhouse gas emissions from fuel use, and decomposition and incineration of waste. Estimated equations are used to simulate industrial futures until 2020, from a system of nonlinear differential equations. Our results demonstrate the economic and physical inter-dependence between material and energy flows and the central role energy prices have in decision-making. For instance, an increase in average energy prices, ceteris paribus , will on average discourage paper recycling, which has implications for greenhouse gas emissions as well as for changes in energy intensity. The analysis of the data reveals diminishing rates of energy self-generation, and the immense longevity of capital, which hampers rapid change in input and carbon intensity. This stresses the importance of investment-led strategies in facilitating faster capital turnover to enhance future sustainability of the system. 相似文献
Manganese (Mn) is an essential trace element that is critical for human health and development. At the turn of the century when diets were based on whole grains, cereals and other traditional foods, Mn intakes (8–9 mg/d) were much greater than that prevalent today (2 mg/d). As societies have developed, diets have shifted as part of a nutrition transition, to those that are high in processed foods, fat, and sugar. These foods are virtually devoid of Mn. Thus, dietary Mn has declined substantially throughout the world, as confirmed by several wide-scale, total diet studies.International variability in dietary Mn is considerable, due to tremendous diversity in food and culture. In countries where fruit and vegetable intake may be limited, i.e. the United Kingdom, populations may ingest much lower levels of Mn (1.4 mg/d) as compared to Asian cultures (4 mg/d) which have an abundance of plant foods in their food supply and cuisine. The bioavailability of Mn must be considered, including chemical form, oxidation state, mineral-mineral interactions, presence of dietary components and traditional food processing techniques (milling, germination, malting, fermentation). Manganese toxicity is a public health problem that results from exposure to a naturally high water source or contaminated environment of the soil and/or drinking water. In contrast, inadequate intake is associated with adverse health effects such as diabetes, metabolic syndrome, poor birth outcomes and possibly, cancer. Future studies are recommended to set dietary standards for this mineral in countries that lack recommendations to help achieve optimal health. 相似文献
The North American beaver (Castor canadensis) builds dams that pond water on streams, which provide crucial ecological services to aquatic and riparian ecosystems and enhance biodiversity. Consequently, there is increasing interest in restoring beavers to locations where they historically occurred, particularly in the arid western United States. However, despite often intensive efforts to reintroduce beavers into areas where they were severely reduced in numbers or eliminated due to overharvesting in the eighteenth and nineteenth centuries, beavers remain sparse or missing from many stream reaches. Reasons for this failure have not been well studied. Our goal was to evaluate certain biotic factors that may limit the occurrence of dam‐building beavers in northern New Mexico, including competitors and availability of summer and winter forage. We compared these factors at primary active dams and at control sites located in stream reaches that were physically suitable for dam‐building beavers but where none occurred. Beaver dams mostly occurred at sites that were not grazed or where there was some alternative grazing management, but were mostly absent at sites within Forest Service cattle allotments. Results indicated that cattle grazing influenced the relation between vegetation variables and beaver presence. The availability of willows (Salix spp.) was the most important plant variable for the presence of beaver dams. We conclude that grazing by cattle as currently practiced on Forest Service allotments disrupts the beaver‐willow mutualism, rendering stream reaches unsuitable for dam‐building beavers. We recommend that beaver restoration will require changes to current livestock management practices. 相似文献
Cyclic GMP formation and inositol phospholipid hydrolysis were studied in rat brain slices to determine if the two processes have common origins. Muscarinic cholinergic stimulation enhanced [3H]inositol phosphate ([ 3H]IP) accumulation from slices prelabelled with [3H]inositol but did not affect cyclic GMP formation in the cortex, striatum, or cerebellum. An elevated level of extracellular K+ stimulated accumulation of both cyclic GMP and [3H]IP in cortex slices. The former, but not the latter, was reduced by lipoxygenase and phospholipase A2 inhibition. Calcium channel activation enhanced and blockade reduced K+-stimulated [3H]IP formation without affecting the cyclic GMP level, and there were differences in the Ca2+ requirements for the two responses. Thus, there is no support for the concept that guanylate cyclase activation inevitably accompanies inositol phospholipid breakdown, and the evidence presented demonstrates that K+ stimulation promotes cyclic GMP and [3H]IP accumulation by different transducing pathways. 相似文献
Abstract. In a highly saline environment high rates of ion uptake are required to generate sufficient osmotic pressure to maintain the turgor that is needed for the continued growth of plants. We estimate the rates of net uptake of Cl− and Na+ required by growing cells to sustain cell expansion at an external NaCl concentration of 500 mol m−3. We also estimate the ion fluxes required to regulate turgor of expanding and fully expanded cells during diurnal changes in transpiration. Passive fluxes could contribute significantly to osmotic regulation, but active fluxes are still essential and would consume a substantial amount of energy. We discuss whether a limitation to growth at high salinity would arise from lack of energy, or from insufficient capacity for ion uptake. There is insufficient evidence to choose between these possibilities. 相似文献
The present investigation was designed to study the uptake of67Cu when administered directly, into the portal vein, along with either functose or glucose, by the liver and extrahepatic
tissues. Following weaning, male Sprague-Dawley rats were fed for 3 wk either commercial laboratory ration (chow) or semipurified
diets deficient in Cu (0.6 ppm) or supplemented with Cu (6.0 ppm) and containing 62% carbohydrate as either fructuse or cornstarch.
After an overnight fast, a single dose of rat plasma (0.1 mL) containing fructose or glucose extrinsically labeled with67Cu was injected directly into their portal vein. Although not always statistically significant, rats fed chow retained more
radioactivity in the liver and several extrahepatic tissues when67Cu was administered with fructose than with glucose. Regardless of Cu status, rats fed diets containing fructose retained
more radioactivity in extrahepatic tissues than rats fed starch. There was an increased uptake of67Cu by the liver, blood, muscle, and fat pad when fructose as compared to glucose was injected in combination with the isotope.
These data strongly suggest that Cu requirements or utilization are greater when fructose is the main dietary carbohydrate.
The results may also in part explain the reason for the increased severity of Cu deficiency in rats fed fructose. 相似文献