An objective approach to model reduction: Application to the Sirius wheat model.

An existing simulation model of wheat growth and development, Sirius, was evaluated through a systematic model reduction procedure. The model was automatically manipulated under software control to replace variables within the model structure with constants, individually and in combination. Predictions of the resultant models were compared to growth analysis observations of total biomass, grain yield, and canopy leaf area derived from 9 trials conducted in the UK and New Zealand under optimal, nitrogen limiting and drought conditions. Model performance in predicting these observations was compared in order to evaluate whether individual model variables contributed positively to the overall prediction. Of the 1 1 1 model variables considered 16 were identified as potentially redundant. Areas of the model where there was evidence of redundancy were: (a) translocation of biomass carbon to grain; (b) nitrogen physiology; (c) adjustment of air temperature for various modelled processes; (d) allowance for diurnal variation in temperature; (e) vernalisation (f) soil nitrogen mineralisation (g) soil surface evaporation. It is not suggested that these are not important processes in real crops, rather, that their representation in the model cannot be justified in the context of the analysis. The approach described is analogous to a detailed model inter-comparison although it would be better described as a model intra-comparison as it is based on the comparison of many simplified forms of the same model. The approach provides automation to increase the efficiency of the evaluation and a systematic means of increasing the rigour of the evaluation.

Methane emissions among individual dairy cows during milking quantified by eructation peaks or ratio with carbon dioxide.

The aims of this study were to compare methods for examining measurements of CH4 and CO2 emissions of dairy cows during milking and to assess repeatability and variation of CH4 emissions among individual dairy cows. Measurements of CH4 and CO2 emissions from 36 cows were collected in 3 consecutive feeding periods. In the first period, cows were fed a commercial partial mixed ration (PMR) containing 69% forage. In the second and third periods, the same 36 cows were fed a high-forage PMR ration containing 75% forage, with either a high grass silage or high maize silage content. Emissions of CH4 during each milking were examined using 2 methods. First, peaks in CH4 concentration due to eructations during milking were quantified. Second, ratios of CH4 and CO2 average concentrations during milking were calculated. A linear mixed model was used to assess differences between PMR. Variation in CH4 emissions was observed among cows after adjusting for effects of lactation number, week of lactation, diet, individual cow, and feeding period, with coefficients of variation estimated from variance components ranging from 11 to 14% across diets and methods of quantifying emissions. No significant difference was detected between the 3 PMR in CH4 emissions estimated by either method. Emissions of CH4 calculated from eructation peaks or as CH4 to CO2 ratio were positively associated with forage dry matter intake. Ranking of cows according to CH4 emissions on different diets was correlated for both methods, although rank correlations and repeatability were greater for CH4 concentration from eructation peaks than for CH4-to-CO2 ratio. We conclude that quantifying enteric CH4 emissions either using eructation peaks in concentration or as CH4-to-CO2 ratio can provide highly repeatable phenotypes for ranking cows on CH4 output.

Variation among individual dairy cows in methane measurements made on farm during milking.

The objective of this study was to quantify on-farm variation between and within cows in methane emissions measured during milking, and to determine which factors are related to this variation. Methane emission rate during milking (MERm) was recorded at milking using methane analyzers installed in automatic (robotic) milking stations for 215 cows over a period of 5 mo. Between-cow variation in MERm (mean 2.07, SD 0.629 g/min), was greater than within-cow variation and was related to variation in body weight, milk yield, parity, and week of lactation. Estimation of daily methane emissions from MERm data, using an equation derived from comparisons with respiration chamber data, produced estimates that ranged from 278 to 456 g of CH4/d and were commensurate with values predicted from metabolizable energy requirements for observed body weight and milk yield. It is concluded that methane emissions vary considerably between dairy cows housed under commercial conditions. This variation needs to be taken into account when performing inventories or testing mitigation strategies, but it might offer opportunities for genetic selection.

On-farm methane measurements during milking correlate with total methane production by individual dairy cows.

The objective of this study was to investigate whether measurement of methane emissions by individual dairy cows during milking could provide a useful technique for monitoring on-farm methane emissions. To quantify methane emissions from individual cows on farm, we developed a novel technique based on sampling air released by eructation during milking. Eructation frequency and methane released per eructation were used to estimate methane emission rate. For 82 cows, methane emission rate during milking increased with daily milk yield (r = 0.71), but varied between individuals with the same milk yield and fed the same diet. For 12 cows, methane emission rate recorded during milking on farm showed a linear relationship (R² = 0.79) with daily methane output by the same cows when housed subsequently in respiration chambers. For 42 cows, the methane emission rate during milking was greater on a feeding regimen designed to produce high methane emissions, and the increase compared with a control regimen was similar to that observed for cows in respiration chambers. It was concluded that, with further validation, on-farm monitoring of methane emission rate during milking could provide a low-cost reliable method to estimate daily methane output by individual dairy cows, which could be used to study variation in methane, to identify cows with low emissions, and to test outcomes of mitigation strategies.

Spatial variability of organic matter properties determines methane fluxes in a tropical forested peatland.

Tropical peatland ecosystems are a significant component of the global carbon cycle and feature a range of distinct vegetation types, but the extent of links between contrasting plant species, peat biogeochemistry and greenhouse gas fluxes remains unclear. Here we assessed how vegetation affects small scale variation of tropical peatland carbon dynamics by quantifying in situ greenhouse gas emissions over 1 month using the closed chamber technique, and peat organic matter properties using Rock-Eval 6 pyrolysis within the rooting zones of canopy palms and broadleaved evergreen trees. Mean methane fluxes ranged from 0.56 to 1.2 mg m-2 h-1 and were significantly greater closer to plant stems. In addition, pH, ranging from 3.95 to 4.16, was significantly greater closer to stems. A three pool model of organic matter thermal stability (labile, intermediate and passive pools) indicated a large labile pool in surface peat (35-42%), with equivalent carbon stocks of 2236-3065 g m-2. Methane fluxes were driven by overall substrate availability rather than any specific carbon pool. No peat properties correlated with carbon dioxide fluxes, suggesting a significant role for root respiration, aerobic decomposition and/or methane oxidation. These results demonstrate how vegetation type and inputs, and peat organic matter properties are important determinants of small scale spatial variation of methane fluxes in tropical peatlands that are affected by climate and land use change.

Amino acid and fatty acid composition of follicular fluid as predictors of in-vitro embryo development.

The value of using the amino acid and fatty acid composition of follicular fluid as predictors of embryo development was assessed in a bovine model of in-vitro maturation (IVM), IVF and blastocyst culture (IVC). A total of 445 cumulus-oocyte complexes (COC) aspirated from visually healthy follicles underwent IVM and IVF singly (n = 138) or in groups (n = 307). Of these COC, 349 cleaved (78%) following IVF and 112 went on to form blastocysts (32% of cleaved) following IVC. Culture method (singly or in groups) had no effect on development. In contrast to fatty acids, which had no predictive value, the amino acid composition of follicular fluid was associated with morphological assessments of COC quality and with post-fertilization development to the blastocyst stage. Principal component analysis identified two amino acids (i.e. alanine and glycine) that had the highest value for predicting early post-fertilization development. The predictive value of these two amino acids, in terms of the percentage of oocytes that cleaved following IVF, was greatest for COC with the poorest morphological grades but, with respect to blastocyst yields, was independent of morphological grade, and so may serve as a useful additional non-invasive measure of COC quality.

Does the diurnal pattern of enteric methane emissions from dairy cows change over time?

Diet manipulation and genetic selection are two important mitigation strategies for reducing enteric methane (CH4) emissions from ruminant livestock. The aim of this study was to assess whether the diurnal pattern of CH4 emissions from individual dairy cows changes over time when cows are fed on diets varying in forage composition. Emissions of CH4 from 36 cows were measured during milking in an automatic (robotic) milking station in three consecutive feeding periods, for a total of 84 days. In Periods 1 and 2, the 36 cows were fed a high-forage partial mixed ration (PMR) containing 75% forage, with either a high grass silage or high maize silage content. In Period 3, cows were fed a commercial PMR containing 69% forage. Cows were offered PMR ad libitum plus concentrates during milking and CH4 emitted by individual cows was sampled during 8662 milkings. A linear mixed model was used to assess differences among cows, feeding periods and time of day. Considerable variation was observed among cows in daily mean and diurnal patterns of CH4 emissions. On average, cows produced less CH4 when fed on the commercial PMR in feeding Period 3 than when the same cows were fed on high-forage diets in feeding Periods 1 and 2. The average diurnal pattern for CH4 emissions did not significantly change between feeding periods and as lactation progressed. Emissions of CH4 were positively associated with dry matter (DM) intake and forage DM intake. It is concluded that if the management of feed allocation remains constant then the diurnal pattern of CH4 emissions from dairy cows will not necessarily alter over time. A change in diet composition may bring about an increase or decrease in absolute emissions over a 24-h period without significantly changing the diurnal pattern unless management of feed allocation changes. These findings are important for CH4 monitoring techniques that involve taking measurements over short periods within a day rather than complete 24-h observations.

The emergent rhizosphere: imaging the development of the porous architecture at the root-soil interface.

The rhizosphere is the zone of soil influenced by a plant root and is critical for plant health and nutrient acquisition. All below ground resources must pass through this dynamic zone prior to their capture by plant roots. However, researching the undisturbed rhizosphere has proved very challenging. Here we compare the temporal changes to the intact rhizosphere pore structure during the emergence of a developing root system in different soils. High resolution X-ray Computed Tomography (CT) was used to quantify the impact of root development on soil structural change, at scales relevant to individual micro-pores and aggregates (µm). A comparison of micro-scale structural evolution in homogenously packed soils highlighted the impacts of a penetrating root system in changing the surrounding porous architecture and morphology. Results indicate the structural zone of influence of a root can be more localised than previously reported (µm scale rather than mm scale). With time, growing roots significantly alter the soil physical environment in their immediate vicinity through reducing root-soil contact and crucially increasing porosity at the root-soil interface and not the converse as has often been postulated. This 'rhizosphere pore structure' and its impact on associated dynamics are discussed.

"Who's been a good dog?" - Owner perceptions and motivations for treat giving.

Complex relationships commonly exist between owners and their companion animals, particularly around feeding behaviour with an owner's affection or love for their animal most pronounced through the provision of food. It is notable that the pet food market is experiencing strong year-on-year growth in sales of dog and cat treats. Recognising the impact of treat giving in pet nutrition, the objective of the study was to investigate owner attitudes and motivations towards feeding treats (shop bought and other) to their dogs. A researcher-mediated questionnaire consisting of both quantitative and qualitative questions was used to interview dog owners (n=280) at two locations: an out-of-town retail park and a country park in the East Midlands. Owners almost unanimously viewed the word 'treat' within a nutritional context, as opposed to a new toy or other pleasure. The majority (96%) of owners interviewed reported feeding treats to their dog, with 69% feeding shop-bought treats on a daily basis. A wide range of treats was reportedly given by owners and the majority of owners interviewed fed multiple treat types. No association was found between owner age and frequency of shop-bought treats fed (P=0.659) nor between owner age and frequency of food given to the dog from the owner's plate (P=0.083). A wide range of foods which would not be considered balanced for the animal's nutritional requirements was viewed as a treat by some dog owners. A range of positive and negative views around the feeding of treats were expressed by dog owners, with some citing beneficial effects while others were clearly aware of the association between treat feeding and potential weight gain/obesity. Owner views included themes around positive reinforcement and responsibility but also reflected relational aspects of the human-animal bond. The results of the study show that treat giving is commonplace in feeding regimes and that treats are embedded in the feeding behaviour of many dog owners. However, the different views expressed around the motivations for, and feeding of, dog treats, reinforce the need to better understand owner psychology linked to this area, and the role this may play in the growing pet obesity epidemic.

Some foliar characteristics of ash trees (Fraxinus excelsior) exposed to ozone episodes.

Young ash trees (Fraxinus excelsior L.) growing in the field were exposed to episodes of 150 nl 1-1 ozone, or to clean air, in open-top chambers at the University of Nottingham, Sutton Bonington Campus, UK, May-October, 1992-1994. The episodes were for 8 h daily and for 1-4 d in succession, with seasonal totals of 24-27 d. A nondestructive method for estimating whole-tree leaf area was developed in 1992 and used to monitor leaf area, leaf number and leaf size in 1993 and 1994. Stomatal density and leaf abscission were also studied. No effects of exposure to ozone on leaf area and leaf number were detected. In 1994 there were consistent trends towards greater mean leaf size and higher stomatal density in trees exposed to ozone, but these effects were not significant at the 95% confidence level. Leaf abscission was slower in trees exposed to ozone in 1992 and 1994, but not in 1993 when there were fewer exposure days late in the season.

Steps in predicting the relationship of yield on fungicide dose.

ABSTRACT A set of hypothetical steps has been defined, which links fungicide dose to marketable yield, whereby (i) increasing dose decreases symptom area, according to a dose-response curve, (ii) decreased symptom area increases crop green area index (GAI), (iii) increasing GAI increases fractional interception of photosynthetically active radiation, (iv) increased fractional interception increases crop dry matter accumulation, and (v) yield increases, depending on the partitioning of dry matter to the marketable fraction. One equation represented all five steps. By integrating this equation for light interception during the yield forming period and differentiating with respect to the ratio of fungicide cost over yield value, an analytical solution was obtained for the economic optimum dose. Taking published ranges of parameter values for the Septoria tritici wheat pathosystem as an example, yield-response curves and optimum doses were biologically plausible when compared with data from four field experiments. The analytical and empirical results imply that the dose required to optimize economic return will vary substantially between sites, seasons, and cultivars. Sensitivity analyses identified parameters describing specific facets of disease severity, fungicide efficacy, and assimilate partitioning as most influential in determining the dose optimum.

Effects of elevated carbon dioxide and ozone on the growth and yield of potatoes (Solanum tuberosum) grown in open-top chambers.

Potato (Solanum tuberosum cv. Bintje) was grown in open-top chambers under three carbon dioxide (ambient and seasonal mean concentrations of 550 and 680 mumol mol-1 CO2) and two ozone concentrations (ambient and an 8 h day-1 seasonal mean of 50 nmol mol-1 O3) between emergence and final harvest. Periodic non-destructive measurements were made and destructive harvests were carried out at three key developmental stages (24, 49 and 101 days after emergence) to establish effects on growth and tuber yield. Season-long exposure to elevated O3 reduced above-ground dry weight at final harvest by 8.4% (P < 0.05), but did not affect tuber yields. There was no significant interaction between CO2 and O3 for any of the growth and yield variables examined. Non-destructive analyses revealed no significant effect of elevated CO2 on plant height, leaf number or green leaf area ratio. However, destructive harvests at tuber initiation and 500 degrees Cd after emergence showed that above-ground dry weight (8 and 7% respectively) and tuber yield (88 and 44%) were significantly increased (P < 0.05) in the 550 mumol mol-1 CO2 treatment. Responses to 550 and 680 mumol mol-1 CO2 were not significantly different for most parameters examined, suggesting the existence of an upper limit to the beneficial influence of CO2 enrichment. Significant effects on above-ground dry weight and tuber yield were no longer apparent at final harvest, although tuber numbers were increased (P < 0.05) under elevated CO2, particularly in the smaller size categories. The results show that the O3 treatment imposed was insufficient to reduce tuber yields and that, although elevated CO2 enhanced crop growth during the early stages of the season, this beneficial effect was not sustained to maturity.

Nutritional manipulation of growth and metabolic and reproductive status in prepubertal gilts.

Reproductive status, metabolic state, and carcass composition were compared in prepubertal littermate gilts of 85 kg BW and identical ages after allocation to one of two feeding regimens at 75 kg, either twice-daily feeding to appetite up to 85 kg and then maintenance feeding until slaughter (Group 85AR) or an initial period of maintenance feeding at 75 kg and then feeding to appetite to reach 85 kg (Group 85RA). Other littermates were studied at the start of treatment (Group 75C) and after the initial period of feeding to appetite (Group 85A) or maintenance feeding (Group 75R). In the absence of differences in backfat depth or longissimus muscle area, Group 85RA gilts showed increased follicular development (P < .001) compared with their feed-restricted Group 85AR littermates. Plasma LH (P < .001) and FSH (P < .02) responses to an LHRH challenge differed between these same groups. Feed restriction reduced preprandial glucose, postprandial cortisol, and insulin (P < .05), total plasma IGF-I, and basal and postprandial free triiodothyronine (T3; all P < .001) at all stages of the experiment. Postprandial insulin, pre- (P < .001) and postprandial free T3, and plasma IGF-I (P < .001) increased in response to refeeding (Group 75R vs 85RA). These data indicate that changes in metabolic status can mediate short-term nutritional effects on reproductive function, in the absence of changes in age, weight, and widely used indices of body composition, and also establish the short-term, feed-restricted, prepubertal gilt as an effective model for studying the mechanisms mediating nutrition-reproduction interactions.

Prediction of the apparent metabolizable energy content of fats fed to broiler chickens.

Soybean oil and tallow acid oil were blended in the ratio 75:25, 50:50, and 25:75 to give 3 blends (A, B, and C) of increasing free fatty acid (FFA) content but decreasing ratio of unsaturated to saturated fatty acids (U:S). Tallow and soybean acid oil were blended in similar proportions to give three blends (D, E, and F) of increasing FFA content and increasing U:S ratio. The six fats were incorporated into a basal diet at rates of 40, 80, and 120 g/kg. Experimental diets were evaluated for apparent available fat (AAF) with broilers aged 1.5 and 7.5 wk of age. The AAF of fats was calculated from extrapolation of the regression of AAF of diets to rate of inclusion of fats. The AME of fats was determined as the product of AAF and gross energy. Increasing FFA content but reducing U:S ratio lowered the AME giving 31.1, 28.7, and 21.7 MJ/kg (1 MJ = .239 Mcal) and 33.2, 31.5, and 28.4 MJ/kg, respectively, for A, B, and C for young and old birds. Corresponding data for D, E, and F (increasing FFA content and U:S ratio) were 27.7, 28.0, and 29.4 MJ/kg and 31.8, 32.9, and 33.3 MJ/kg, respectively, for young and old birds. Data generated, together with results from previous reports, were subject to regression analysis. The AME of fats could be predicted from knowledge of U:S ratio and FFA content with equations accounting for .816 and .925 of the variation in AME values for young and old birds, respectively.

Variation in enteric methane emissions among cows on commercial dairy farms.

Methane (CH4) emissions by dairy cows vary with feed intake and diet composition. Even when fed on the same diet at the same intake, however, variation between cows in CH4 emissions can be substantial. The extent of variation in CH4 emissions among dairy cows on commercial farms is unknown, but developments in methodology now permit quantification of CH4 emissions by individual cows under commercial conditions. The aim of this research was to assess variation among cows in emissions of eructed CH4 during milking on commercial dairy farms. Enteric CH4 emissions from 1964 individual cows across 21 farms were measured for at least 7 days/cow using CH4 analysers at robotic milking stations. Cows were predominantly of Holstein Friesian breed and remained on the same feeding systems during sampling. Effects of explanatory variables on average CH4 emissions per individual cow were assessed by fitting a linear mixed model. Significant effects were found for week of lactation, daily milk yield and farm. The effect of milk yield on CH4 emissions varied among farms. Considerable variation in CH4 emissions was observed among cows after adjusting for fixed and random effects, with the CV ranging from 22% to 67% within farms. This study confirms that enteric CH4 emissions vary among cows on commercial farms, suggesting that there is considerable scope for selecting individual cows and management systems with reduced emissions.

Does consumption of leafy vegetables grown in peri-urban agriculture pose a risk to human health?

Concentrations of potentially toxic elements were measured in soils and five contrasting tropical leafy vegetables grown in a replicated field trial at five contaminated urban agriculture sites in Kampala City, Uganda. Soil contamination at each site could be tentatively ascribed to known waste disposal practices. There was considerable variation in metal uptake between vegetable types. Washing leafy vegetables reduced chromium and lead concentrations but exogenous contamination of leaves also depended on vegetable type, with Gynandropsis gynandra L. showing a marked tendency to accumulate Pb and Cr. For the worst case scenario of children consuming unwashed vegetables, some metal 'hazard quotient' (HQ) limits (1.0) were violated at four of the five sites studied. For the 25 'site-vegetable' combinations assessed, the HQ for Pb exceeded 1.0 in 36% of cases. A vegetable-specific site screening tool based on soil extraction with 0.01 M CaCl(2) and extrapolation to provide HQ values was assessed.

Canine obesity: is there a difference between veterinarian and owner perception?

OBJECTIVES: The overall aim of this study was to examine the nature of the relationship between dog-ownership and canine obesity, explored in two cohorts of overweight/obese or non-overweight dogs (n=125). This paper concentrates on the owners' perception of dog weight. METHODS: A researcher-mediated questionnaire was used to collect data from dog owners attending a small veterinary practice. Interviewees (n=121) were asked qualitative and quantitative questions, designed to examine the owners' views of their relationship with their dogs. RESULTS: Although a high proportion of owners claimed to have discussed the dog's weight with their veterinarian, some discrepancies were apparent between owner perception of animal weight and the veterinarian's evaluation of body condition score. Owner disagreement was significantly greater for the veterinarian-defined overweight dogs (P=0·005). Owners often provide personal narratives to account for their dog's weight status. CLINICAL SIGNIFICANCE: This study confirms the important role of the vet in providing information about the issue of dog weight but also suggests that providing verbal information is sometimes insufficient. The study also indicates the potential value of qualitative research methods to further understand client perception of complex animal care issues and highlights the need for further in-depth research.

Physiological temperature variants and culture media modify meiotic progression and developmental potential of pig oocytes in vitro.

Ovarian follicles in vivo are cooler than surrounding abdominal and ovarian tissues. This study investigated whether typical follicular temperatures influence the maturation and developmental potential of pig oocytes in vitro. Oocytes were synchronised at the germinal vesicle (GV) stage and incubated at 39, 37 or 35.5 degrees C. When compared with 39 degrees C, which is often used for in vitro studies, lower temperatures delayed spontaneous progression to the metaphase I and II (MI and MII) stages of meiosis. The MII was delayed by about 12 h per degrees C. All oocytes had normal morphology. Oocytes reaching GV breakdown (GVBD) at 39 degrees C were subsequently unaffected by cooling, demonstrating thermal sensitivity during the pre-GVBD stage only. Simultaneous assay of maturation-controlling kinases (maturation promoting factor (MPF) and MAPK) showed that cooling delayed kinase activation, provided it was applied prior to GVBD. Activity profiles remained coupled to the stage of meiosis. Neither enzyme was directly thermally sensitive over this temperature range. Following in vitro fertilisation, fewer blastocysts developed from embryos derived from 35.5 or 37 degrees C oocytes as compared with those from 39 degrees C oocytes. Manipulation of fertilisation timings to allow for delayed maturation showed that over-maturing or aging at lower temperatures compromises subsequent embryo development, despite normal nuclear maturation; the GV stage was again the thermally sensitive period. Cleavage rates were improved by the culture of oocytes with follicle-stimulating hormone (FSH) at 37 but not at 35.5 degrees C. Inclusion of 20% follicular fluid in the oocyte medium restored the blastocyst rate to that seen at higher temperatures. Thus, FSH and follicular fluid may allow oocytes to achieve normal developmental potential at in vivo temperatures.