Milking cows typically dominate dairy farm greenhouse gas (GHG) emissions, but replacement heifers also contribute to farm emissions and can increase the emission intensity of milk production. In northern Australia, heifers generally graze poorer-quality subtropical pastures and in the absence of energy-dense supplementary feed during periods of low pasture growth, liveweight (LW) gain can be restricted. This modelling study examined the time required and enteric methane (CH4) emissions produced in raising dairy heifers to a target LW for first mating by feeding a diet assuming either constant (static) or variable (dynamic) nutritive values. Using a static approach (Australian Feeding Standards methodology), and assuming a target mating LW of 360 kg, growing heifers reached their target LW at ~18 months of age while consuming C4 grasses with a constant metabolisable energy content of 9.5 MJ/kg dry matter (DM) or 11 months of age on a diet of 11.0 MJ/kg DM. Enteric CH4 emissions were 1.2 and 0.8 t of carbon dioxide equivalents/heifer over the 18- and 11-month periods, respectively. To explore the extent with which climatic conditions influence seasonal pasture availability and nutritive value with a dynamic approach, we used a whole-farm biophysical model (SGS pasture model) to simulate diets with mean metabolisable energy values of 9.5 and 10.9 MJ/ kg DM. On average (±s.d.), heifers required 22 ± 4 and 17 ± 1 months, respectively, to reach target LW, with cumulative enteric CH4 emissions of 1.22 ± 0.20 and 0.72 ± 0.04 t carbon dioxide equivalents, respectively. The dynamic approach resulted in slower LW gain due to the variable nutritive value of the diet throughout the year, resulting in seasonal periods of LW plateauing or decline. Maintaining heifers on high-quality diets in subtropical northern Australia should result in increased daily LW gain, lower enteric CH4 emissions to mating LW and earlier calving. Together, these factors reduce their lifetime emission intensity of milk production.

2008-06-01·Educational Action Research

When students negotiate: an action research case study of a Year 8 English class in a secondary college in Victoria, Australia

作者: Carlyn Sproston

This article is the story of what happens when students are given the opportunity to be part of the decision‐making process, both in the negotiation of what takes place in the classroom and in the ‘action’ of the action research process itself. An action research approach was used as the most appropriate method by which to analyse the experiences of students and teacher as they negotiated three action research cycles in their Year 8 English classes. Specifically, the research focused on the connection between negotiated learning and motivation. Results suggest that students experience greater commitment and motivation when they are given opportunities to be actively involved in contributing to their own learning, and point to the value of action research as a method for improving teaching practice. This article is of particular interest to educators of middle‐years students because it addresses the perceived challenges of educating young adolescents, particularly those at the Year 8 level.

Medicine, Health and Being Human

作者: Lesa Scholl

100 项与 Emmanuel College, University of Queensland 相关的药物交易

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100 项与 Emmanuel College, University of Queensland 相关的转化医学

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