Cottle D.J.,University of New England of Australia |
Velazco J.,University of New England of Australia |
Hegarty R.S.,University of New England of Australia |
Mayer D.G.,Ecosciences Precinct
Animal | Year: 2015
Spot measurements of methane emission rate (n = 18 700) by 24 Angus steers fed mixed rations from GrowSafe feeders were made over 3- to 6-min periods by a GreenFeed emission monitoring (GEM) unit. The data were analysed to estimate daily methane production (DMP; g/day) and derived methane yield (MY; g/kg dry matter intake (DMI)). A one-compartment dose model of spot emission rate v. time since the preceding meal was compared with the models of Wood (1967) and Dijkstra et al. (1997) and the average of spot measures. Fitted values for DMP were calculated from the area under the curves. Two methods of relating methane and feed intakes were then studied: the classical calculation of MY as DMP/DMI (kg/day); and a novel method of estimating DMP from time and size of preceding meals using either the data for only the two meals preceding a spot measurement, or all meals for 3 days prior. Two approaches were also used to estimate DMP from spot measurements: fitting of splines on a ‘per-animal per-day’ basis and an alternate approach of modelling DMP after each feed event by least squares (using Solver), summing (for each animal) the contributions from each feed event by best-fitting a one-compartment model. Time since the preceding meal was of limited value in estimating DMP. Even when the meal sizes and time intervals between a spot measurement and all feeding events in the previous 72 h were assessed, only 16.9% of the variance in spot emission rate measured by GEM was explained by this feeding information. While using the preceding meal alone gave a biased (underestimate) of DMP, allowing for a longer feed history removed this bias. A power analysis taking into account the sources of variation in DMP indicated that to obtain an estimate of DMP with a 95% confidence interval within 5% of the observed 64 days mean of spot measures would require 40 animals measured over 45 days (two spot measurements per day) or 30 animals measured over 55 days. These numbers suggest that spot measurements could be made in association with feed efficiency tests made over 70 days. Spot measurements of enteric emissions can be used to define DMP but the number of animals and samples are larger than are needed when day-long measures are made. © The Animal Consortium 2015
Pagendam D.E.,Ecosciences Precinct |
Percival D.B.,University of Washington
Water Resources Research | Year: 2015
Detiding end-of-catchment flow data are an important step in determining the total volumes of freshwater (and associated pollutant loads) entering the ocean. We examine three approaches for separating freshwater and tidal flows from tidally affected data: (i) a simple low-pass Butterworth filter (BWF); (ii) a robust, harmonic analysis with Kalman smoothing (RoHAKS) which is a novel approach introduced in this paper; and (iii) dynamic harmonic regression (DHR). Using hydrographic data collected in the Logan River, Australia, over a period of 452 days, we judge the accuracy of the three methods based on three criteria: consistency of freshwater flows with upstream gauges; consistency of total discharge volumes with the raw data over the event; and minimal upstream flow. A simulation experiment shows that RoHAKS outperforms both BWF and DHR on a number of criteria. In addition, RoHAKS enjoys a computational advantage over DHR in speed and use of freely available software. Key Points: RoHAKS gives improved estimates of freshwater flow Detiding methods can exhibit periods of upstream flow Detiding based on robust statistical methods shows improved performance © 2015 Commonwealth Scientific and Industrial Research Organisation, Australia. Water Resources Research © 2015 American Geophysical Union.
Dundon S.G.,LEP Consultant |
Mayer D.G.,Ecosciences Precinct
Small Ruminant Research | Year: 2015
Summer in the Persian Gulf region presents physiological challenges for Australian sheep that are part of the live export supply chain coming from the Australian winter. Many feedlots throughout the Gulf have very high numbers of animals during June to August in order to cater for the increased demand for religious festivals. From an animal welfare perspective it is important to understand the necessary requirements of feed and water trough allowances, and the amount of pen space required, to cope with exposure to these types of climatic conditions. This study addresses parameters that are pertinent to the wellbeing of animals arriving in the Persian Gulf all year round.Three experiments were conducted in a feedlot in the Persian Gulf between March 2010 and February 2012, totalling 44 replicate pens each with 60 or 100 sheep. The applied treatments covered animal densities, feed-bunk lengths and water trough lengths. Weights, carcass attributes and health status were the key recorded variables. Weight change results showed superior performance for animal densities of ≥1.2m2/head during hot conditions (24-h average temperatures greater than 33°C, or a diurnal range of around 29-37°C). However the space allowance for animals can be decreased, with no demonstrated detrimental effect, to 0.6m2/head under milder conditions. A feed-bunk length of ≥5cm/head is needed, as 2cm/head showed significantly poorer animal performance. When feeding at 90% ad libitum 10cm/head was optimal, however under a maintenance feeding regime (1kg/head/day) 5cm/head was adequate. A minimum water trough allowance of 1cm/head is required. However, this experiment was conducted during milder conditions, and it may well be expected that larger water trough lengths would be needed in hotter conditions.Carcass weights were determined mainly by weights at feedlot entry and subsequent weight gains, while dressing percentage was not significantly affected by any of the applied treatments. There was no demonstrated effect of any of the treatments on the number of animals that died, or were classified as unwell. However, across all the treatments, these animals lost significantly more weight than the healthy animals, so the above recommendations, which are aimed at maintaining weight, should also be applicable for good animal health and welfare.Therefore, best practice guidelines for managing Australian sheep in Persian Gulf feedlots in the hottest months (June-August) which present the greatest environmental and physical challenge is to allow feed-bunk length 5cm/head on a maintenance-feeding program and 10cm/head for 90% ad libitum feeding, and the space allowance per animal should be ≥1.2m2/head. Water trough allocation should be at least 1cm/head with provision for more in the summer when water intake potentially doubles. © 2015.
Kienzle M.,Ecosciences Precinct |
Kienzle M.,University of Queensland
Journal of Agricultural, Biological, and Environmental Statistics | Year: 2016
Fisheries management agencies around the world collect age data for the purpose of assessing the status of natural resources in their jurisdiction. Estimates of mortality rates represent a key information to assess the sustainability of fish stocks exploitation. Contrary to medical research or manufacturing where survival analysis is routinely applied to estimate failure rates, survival analysis has seldom been applied in fisheries stock assessment despite similar purposes between these fields of applied statistics. In this paper, we developed hazard functions to model the dynamic of an exploited fish population. These functions were used to estimate all parameters necessary for stock assessment (including natural and fishing mortality rates as well as gear selectivity) by maximum likelihood using age data from a sample of catch. This novel application of survival analysis to fisheries stock assessment was tested by Monte Carlo simulations to assert that it provided unbiased estimations of relevant quantities. The method was applied to the data from the Queensland (Australia) sea mullet (Mugil cephalus) commercial fishery collected between 2007 and 2014. It provided, for the first time, an estimate of natural mortality affecting this stock: (Formula presented.) year (Formula presented.). © 2015, International Biometric Society.
Dang A.,03 Tor Street |
Dang A.,University of Southern Queensland |
Silburn M.,03 Tor Street |
Silburn M.,University of Southern Queensland |
And 2 more authors.
Journal of Agricultural and Food Chemistry | Year: 2016
Herbicides are often applied to crop residues, but their fate has not been well studied. We measured herbicide washoff from sugar cane trash during simulated rainfall, at 1, 8, and 40 days after spraying (DAS), to provide insight into herbicide fate and for use in modeling. Herbicides included are commonly used in the sugar industry, either in Australia or in Brazil. Concentrations of all herbicides and applied Br tracer in washoff declined exponentially over time. The rate of washoff during rainfall declined with increasing DAS. Cumulative washoff as a function of rainfall was similar for most herbicides, although the most soluble herbicides did have more rapid washoff. Some but not all herbicides became more resistant to washoff with increasing DAS. Of the total mass washed off, 80% washed off in the first 30 mm (∼40 min) of rainfall for most herbicides. Little herbicide remained on the trash after rainfall, implying nearly complete washoff. © 2016 American Chemical Society.