The risk and control of Salmonella outbreaks in calf-raising operations: a mathematical modeling approach

Salmonellosis in calves has economic and welfare implications, and serves as a potential source of human infections. Our objectives were to assess the risk of Salmonella spread following its introduction into a herd of pre-weaned calves and to evaluate the efficacy of control strategies to prevent and control outbreaks. To meet these objectives, we developed a model of Salmonella transmission within a pre-weaned group of calves based on a well documented outbreak of salmonellosis in a calf-raising operation and other literature. Intervention scenarios were evaluated in both deterministic and stochastic versions of the model. While the basic reproduction number (R0) was estimated to be 2.4, simulation analysis showed that more than 60% of the invasions failed after the introduction of a single index case. With repeated introduction of index cases, the probability of Salmonella spread was close to 1, and the tested control strategies were insufficient to prevent transmission within the group. The most effective strategies to control ongoing outbreaks were to completely close the rearing operation to incoming calves, to increase the proportion of admitted calves that were immunized (>75%), and to assign personnel and equipment to groups of calves.     

Genetic and environmental control of dormancy in white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Grain dormancy in wheat is an important component of resistance to preharvest sprouting and hence an important trait for wheat breeders. The significant influence of environment on the dormancy phenotype makes this trait an obvious target for marker-assisted-selection. Closely related breeding lines, SUN325B and QT7475, containing a major dormancy QTL derived from AUS1408 located on chromosome 4A, but substantially different in dormancy phenotype, were compared with a non-dormant cultivar, Hartog, in a range of controlled environments. As temperature increased, dormancy at harvest-ripeness decreased particularly for QT7475. The dormancy phenotypes of reciprocal F₁ grains involving all possible combinations of Hartog, QT7475 and SUN325B were also compared in two environments with different temperatures. The results were consistent with the presence of QTL in addition to 4A in SUN325B, compared with QT7475, at least one of which was associated with the seed coat. Genetic analysis of a doubled haploid population derived from SUN325B × QT7475 identified a highly significant QTL located on chromosome 3BL, close to the expected position of the mutant allele of the red seed coat colour gene in white-grained wheat, R-B1a. When the lines in the population were grouped according to the parental alleles at marker loci flanking the 3B QTL, the dormancy phenotype frequency distribution for the SUN325B group was shifted towards greater dormancy compared with the QT7475 group. However, significant variation for dormancy phenotype remained within each group. Lines representing the extremes of the range of phenotypes within each group maintained their relative ranking across seven environments consistent with the presence of another unidentified QTL contributing to dormancy in SUN325B.     

Grain dormancy in fixed lines of white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) grown under controlled environmental conditions

Pre-harvest sprouting (PHS) in wheat (Triticum aestivum L.) can be a significant problem, causing deleterious effects on grain quality. However, the adverse impacts of PHS can be reduced by introgressing genes controlling grain dormancy into white-grained bread wheat. Screening for grain dormancy typically involves germination testing of harvest-ripe grain grown in a glasshouse or field. However, the more uniform environmental conditions provided by temperature controlled glasshouses (i.e. controlled environmental conditions—CEC) may provide significant benefits for the assessment of grain dormancy. In this study, the dormancy phenotype of grain grown under CEC incorporating an extended photoperiod, was compared with 2 years of data from field grown material. Four dormant double haploid lines (derived from SW95-50213 and AUS1408) and two locally adapted non-dormant cultivars EGA Gregory and EGA Wills were compared in three replicated experiments grown under CEC (22 ± 3°C and 24 h photoperiod). The germination response of harvest-ripe grain was examined to assess the expression of grain dormancy. Two measures of germination, the predicted time to 50% germination (G ₅₀) and a weighted germination index, both clearly differentiated dormant and non-dormant lines grown under CEC. In addition, levels of grain dormancy were similar to field-grown plants. These results demonstrated that CEC with an extended photoperiod can be used for rapid and reliable characterisation of grain dormancy in fixed lines of bread wheat.     

Pathway analysis of branched-chain ester biosynthesis in apple using deuterium labeling and enantioselective gas chromatography-mass spectrometry

The biosynthesis of volatile esters by Red Delicious apples was investigated by incubating fruit tissue with deuterated flavor precursors at various times after controlled atmosphere (CA) storage and measuring deuterium incorporation into branched-chain ester volatiles. 2-Methylbutyl acetate was the only volatile not significantly reduced by CA storage. Conversion of 2-methylbutanol to 2-methylbutyl acetate and of 2-methylbutanoic acid to ethyl 2-methylbutanoate and to hexyl 2-methylbutanoate was limited by the availability of 2-methylbutyl substrates but not by acetyl-CoA, ethanol, or hexanol, respectively. The enzymatic activity required for these reactions declined during CA storage. The conversion of 2-methylbutanoic acid to 2-methylbutanol was also substrate limited, but enzymic activity appeared stable in storage. Biosynthesis of both 2-methylbutanoic acid and 2-methylbutanol, from isoleucine, was severely depressed under CA storage. The reduced metabolism of isoleucine to 2-methylbutanoyl-CoA may be the primary reason for reduced branched-chain ester synthesis in CA-stored Red Delicious apples. Enantioselective gas chromatography-mass spectrometry confirmed that the chirality of (S)-2-methylbutyl acetate derives from l-isoleucine with the other enzymes in this pathway not being enantiospecific. Treatment of tissue samples with 2-methylbut-2E-enal gave only (S)-2-methylbutyl acetate, indicating that biosynthesis was not via tiglyl-CoA.     

Effect of C:N Ratio on Microbial Activity and N Retention: Bench-scale Study Using Pulp and Paper Biosolids

The effect of C:N ratio on the performance of bench-scale composting systems treating pulp and paper biosolids was investigated. The biosolids used were obtained from the Pine Falls Paper Company located in Manitoba. The biosolids, on a wet basis, consisted of 41% primary biosolids, 21% secondary biosolids, and 39% deinking plant sludge. The biosolids were mixed with bark to achieve an initial moisture content of 60%, resulting in a recipe consisting of 1.09 kg of bark per kg of biosolids on a dry basis. Four reactors (treatments) were run with C:N ratios of 107 (control; no N supplement), 55, 29, and 18. Each treatment was replicated three times. Sulfur coated urea was used as the N supplement. Parameters monitored included C:N ratio, N recovery, material compaction, temperature, qualitative odor observations, and volatile solids reduction. The relative microbial activity was observed in-directly using volatile solids removal and the relative heat generation data. The data showed a strong negative linear relationship between C:N ratio and relative heat generation (r²=0.98) and between C:N ratio and volatile solids removal (r²=0.84 for all four treatments; and r²=1.0 for C:N = 29 to 107). The data also showed a strong nonlinear relation between N retention and C:N ratio (% retention = 101(1-0.92C:N); r² = 0.71; n = 12). Qualitative odor observations and N losses suggested that a C:N ratio of 18 was too low, therefore a performance comparison was made between the C:N-107 and the C:N-29 treatments. It was observed that the mean volatile solids removal was 28.6% higher in the C:N-29 treatments as compared to the C:N-107 control. While this difference is significant from a bench-scale perspective, the authors question the practical significance of the difference and recommend further investigation.     

Using a Biocell to Measure Effect of Compressive Settlement on Free Air Space and Microbial Activity In Windrow Composting

This paper describes the first equipment developed to include compressive loads in a physical model of the composting environment. This new type of composting reactor was named a biological load cell, or biocell for short. Our hypothesis was that the exclusion of compressive settlement in existing physical models may lead to errors if the data is used to design full-scale windrow composting facilities. Municipal biosolids were mixed with three organic amendments (wood chips, straw, and leaves) to yield mixture moisture contents of 55%. Compressive settlement analyses were completed by subjecting the mixtures to loads of 0, 4.3, 8.6, and 12.9 kPa using biocells. The effect of compressive settlement on microbial activity was investigated using the biosolids:leaf mixture under loaded (12.9 kPa) and unloaded conditions. The settlement behavior of all three mixtures was found to fit established soil compaction equations and new equations were developed to represent the vertical free air space (FAS) and bulk density profiles in composting systems. The FAS profiles indicated that existing physical models do not simulate the FAS conditions within a composting matrix and significant differences in microbial activity were observed between loaded and unloaded biocells. The microbial activity differences were attributed to the reduced FAS within the loaded biocells, which, in consequence, lead to lower pore space oxygen concentrations. It proved difficult, however, to simulate the air flow regime within a windrow composting matrix. To further develop the biocells, there is a need to investigate the in-situ stress conditions and natural draft ventilation rates of full-scale windrow systems. While further work is required to perfect the biocells as a physical model of the windrow composting environment, it has demonstrated its potential use for FAS analysis and as a standard bulk density apparatus. Using biocells, it is recommended that FAS curves be developed for a wide range of feedstock recipes. The biocell apparatus could also be developed as a standard bulk density test apparatus. Other important conclusions drawn from the work include: leaves should not be used as a bulking agent; wood chips showed superior bulking properties and are recommended for use in very high (3.7 m) windrows; straw showed intermediate bulking properties and should not be used for high windrows without further investigation; for all materials, compaction occurred rapidly after each incremental load, suggesting that windrow turning will do little to alleviate a low FAS problem associated with an incorrect composting recipe.     

麦谷蛋白亚基Clu-1和Glu-3位点基因等位变异对小麦品质特性的影响

甲单向一步SDS-PAGE方法分析表明亲本品种Suneca和Cook在麦谷蛋白亚基的5个位点(Glu-B1,Glu-D1,Glu-A3,Glu-B3和Glu-D3)均含不同等位基因。本研究重点对Suneca×Cook的F_4代群体中在麦谷蛋白亚基位点均为纯合基因的60个系的出粉率(FY),面粉蛋白质含量(FP)及和面时间(PTM)进行了分析,以研究麦谷蛋白各亚基位点等位基因变异及位点间互作对小麦品质特性的影响。结果表明,不同基因型间出粉率无显著差异,Glu-D1位点等位基因d和a对FP的效应存在显著差异,Glu-Dld基因(编码5 10亚基)的正效应显著高于Glu-Dla基因(编码2 12亚基);Glu-D1、Glu-A3和Glu-B3位点上基因的等位变异对PTM有显著和极显著影响,含Glu-Dld、Glu-A3b和Glu-B3b基因的系分别比含Glu-Dla,Glu-A3d和Glu-B3h基因的系有较长的和面时间;Glu-B1位点上等位变异i和u以及Glu-D3位点等位基因b和e分别对PTM无明显影响。在这种遗传背景下,麦谷蛋白亚基位点对PTM的效应大小依次排列为Glu-D1>Glu-B3>Glu-A3>GIu-B1=Glu-D3。Glu-1位点和Glu-3位点间对和面特性的影响存在累加效应和互作效应。     

Allelic changes in bread wheat cultivars were associated with long-term wheat trait improvements

Genetic impacts under selective breeding of agricultural crops have been frequently investigated with molecular tools, but inadequate attention has been paid to assess genetic changes under long-term genetic improvement of plant traits. Here we analyzed allelic changes with respect to wheat trait improvement in 78 Canadian hard red spring wheat cultivars released from 1845 to 2004 and screened with 370 mapped SSR markers. The improvements in quality, maturity, yield, disease, stem rust, leaf rust, sawfly resistance, and agronomy were considered. A total of 154 (out of 370) loci with significant allelic changes across 21 chromosomes were detected in the 78 wheat cultivars separated into improved versus non-improved groups for eight traits. The number of significant loci for improving a trait ranged from four for quality to 68 for yield and averaged 35. Many more loci with significant allelic reduction for improving a trait were detected than those with significant allelic increase. Selection for early maturity introduced more alleles, but improving the other traits purged more alleles. Significantly lower numbers of unique alleles were found in the cultivars with improved traits. The distributions of unique allele counts also varied greatly across the 21 chromosomes with respect to trait improvement. Significant SSR variation between two cultivar groups was observed for improvement in seven traits, but not in stem rust. The proportional SSR variation residing between two groups ranged from 0.014 to 0.118. The proportional SSR variations within the improved cultivar groups consistently were much lower than those within the non-improved groups. These findings clearly demonstrate the association between allelic changes and wheat trait improvements and are useful for understanding the genetic modification of the wheat genome by long-term wheat breeding.     

Boreal forest futures: Modelling the controls on tree species range limits and transient responses to climate change

Range limits and broad-scale geographic variations in the productivity of boreal and northern deciduous tree species in Europe are simulated with a bioclimatic model (STASH). STASH is based on a small number of distinct mechanisms by which climate is thought to affect the survival, regeneration and growth of trees. Survival is limited by summer warmth requirements and winter cold tolerance; regeneration, additionally by winter chilling requirements; and growth rate by net assimilation, which in turn is related to photosynthetically active radiation, growing-season length, temperature (relative to species-specific optima) and soil moisture supply (relative to evaporative demand). These mechanisms are quantified either as thresholds (for survival and regeneration) or multipliers (for growth), based on bioclimatic variables computed from monthly climate normals interpolated three-dimensionally to a 10-minute grid. Growing-season and growing degree day calculations take into account the effects of chilling. The drought calculations also take into account the effects of soil-moisture storage by means of a physically based evapotranspiration calculation coupled to a one-layer soil hydrology model. STASH is used to examine changes in potential range limits under a 2xCO₂ climate-change scenario. Associated transient responses at selected sites in the boreal and boreo-nemoral zones of Sweden are also simulated, using the forest gap model FORSKA2. The species-specific survival and regeneration constraints and growth responses of STASH modify the growth, establishment and mortality of trees in FORSKA2. The results obtained in this way differ sharply from the results of conventional forest gap models, where growth rates are assumed to decline to zero at minimum and maximum growing degree day limits. For example, towards the southern limit ofPicea abies (Norway spruce), STASH correctly shows no decline in productivity, but rather an abrupt cut-off corresponding to a chilling requirement during regeneration that is not met further south or west. In transient warming scenarios, this mechanism has the effect that natural regeneration can be blocked due to the warm winters even as yield is increasing due to the longer and warmer summers. STASH predicts drastic changes in species distributions in response to the large climate changes (especially winter warming) expected for northern Europe. Some of the common boreal species (e.g.,Picea abies; Pinus sylvestris; Alnus incana) are unlikely to survive in much of their present range, withdrawing to the far north. Other species already widespread may be able to occupy some of the few sites that are today unavailable to them (e.g.,Betula spp.;Corylus avellana). Other temperate deciduous species such asFagus sylvatica could have dramatic range expansions, potentially occupying large tracts of the present boreal zone. FORSKA2 transient simulations illustrate some of the possible routes towards different types of forest in a changed climate. Some sites in the north show little change in species composition, but sites towards the southern boundary of the boreal zone could develop a new suite of dominants. The degree of sensitivity of a particular site depends both on the climate change prediction and on the transient dynamics of the forest community. Many types of transient behaviour are shown to be possible. Coupled with uncertainties about the future role of dispersal and changes in disturbance rate, the complexity and variety of these transient responses imply a highly uncertain future for the north European boreal forests.