孵化期胚胎温度调控技术

在孵化过程中,温度的控制是至关重要的因素,温度的高低将直接影响出雏的效果.适宜的温度能将弱雏率、毛蛋率、死胚率控制在最低水平,并且孵化出的雏鸡发育良好,体格健壮,为今后的生长发育打下坚实的基础.     

In utero infection of cattle with Mycobacterium avium subsp. paratuberculosis: a critical review and meta-analysis

Mycobacterium avium subsp. paratuberculosis (Mptb) causes Johne's disease in ruminants. Disease control programmes aim to break the faecal-oral cow-calf transmission cycle through hygienic calf rearing and removal of affected cows from the herd, but these programmes do not take account of the potential for congenital infection. The aims of this study were to critically review research on in utero infection, determine the prevalence of fetal infection in cattle through meta-analysis and estimate the incidence of calves infected via the in utero route. About 9% (95% confidence limits 6-14%) of fetuses from subclinically infected cows and 39% (20-60%) from clinically affected cows were infected with Mptb (P<0.001). These are underestimates for methodological reasons. The estimated incidence of calf infection derived via the in utero route depends on within-herd prevalence and the ratio of sub-clinical to clinical cases among infected cows. Assuming 80:20 for the latter, estimates of incidence were in the range 0.44-1.2 infected calves per 100 cows per annum in herds with within-herd prevalence of 5%, and 3.5-9.3 calves in herds with 40% prevalence. These estimates were not markedly sensitive to the value chosen for the proportion of clinical cases. In utero transmission of Mptb could retard the success of disease control programmes if the opportunities for post natal transmission via colostrum/milk and environmental contamination were able to be controlled. The consequences of fetal infection for the calves so infected are discussed in the context of diagnosis and vaccination together with recommendations for future research.     

Estimating Distance Sampling Detection Functions When Distances Are Measured With Errors

Distance sampling methods assume that distances are known but in practice there are often errors in measuring them. These can have substantial impact on the bias and precision of distance sampling estimators. In this paper we develop methods that accommodate both systematic and stochastic measurement errors. We use the methods to estimate detection probability in two surveys with substantial measurement error. The first is a shipboard line transect survey in the North Sea in which information on measurement error comes from photographically measured distances to a subset of detections. The second is an aerial cue-counting survey off Iceland in which information on measurement error comes from pairs of independently estimated distances to a subset of detections. Different methods are required for measurement error estimation in the two cases. We investigate by simulation the properties of the new estimators and compare them to conventional estimators. They are found to perform better than conventional estimators in the presence of measurement error, more so in the case of cue-counting and point transect estimators than line transect estimators. An appendix on the asymptotic distributions of conditional and full likelihood estimators is available online.     

Organic‐carbon fractions in an agricultural topsoil assessed by the determination of the soil mineral surface area

According to recent conceptual models, the organic carbon (OC) of soils can be divided into OC fractions of increasing stability from labile free OC to resistant OC associated with the soil mineral phase. In this study, we present a method for quantifying two OC fractions based on soil aggregate–size fractionation and the N₂ gas–adsorption method. For this purpose, we analyzed soil material of the plow layer of a Haplic Chernozem subjected to different fertilizer treatments (no fertilizer, mineral fertilizer, mineral and organic fertilizer). The total organic‐C concentration (TOC) and the clay content of the different size fractions were determined as well as the specific surface area (SSA_mineral) and the sample pore volume after thermal oxidation (OC‐free). The TOC of the different soil‐aggregate fractions was linearly related to SSA_mineral. Clay‐associated OC and nonassociated OC fractions of the different soil samples were quantified using two methods based on the OC surface loading at the clay fraction. The application of organic fertilizer increased the amount of nonassociated OC but hardly affected the concentration of clay‐associated OC. This finding agrees with previous studies on C dynamics in soils and indicates a finite capacity of soil materials to sequester OC. Even without any addition of organic fertilizer, the mineral phase of the analyzed soil material appears to be C‐saturated.     

Removal of short‐range‐order minerals prior to grain‐size analysis of volcanic ash soils

Incomplete dispersion of aggregates is a well‐known difficulty when analyzing soil texture of Andosols, particularly if no fresh soil material is available. To facilitate such investigations, several dispersion procedures were carried out on air‐dried samples rich in short‐range‐order minerals, originating from selected Andosol profiles (S Mexico). As a result, we propose an improved method based on a sequential chemical treatment with K oxalate, NH₄ oxalate, and oxalic acid that reliably removes cementing agents and allows for a stable dispersion of soil particles after addition of Na pyrophosphate. This method was proved to be well reproducible and highly reliable for routine grain‐size determinations. The potential error caused by the inherent risk of dissolving primary minerals or fresh volcanic glass remains far beyond the analytical error resulting from the incomplete and irreproducible dispersion of highly resistant aggregates by other commonly used techniques.     

Arbuscular mycorrhizal association is beneficial for growth and detoxification of xenobiotics of barley under drought stress

Background, aim, and scope  

Plant growth and productivity under abiotic stresses such as water shortage or pollution are major problems which currently worry scientists in the field of food production and plant health. Since the intensification of livestock production with its associated increased demand for fodder has encouraged farmers to rely more heavily on chemical fertilizers, very often, municipal waste and wastewater sludge is considered a possible source of plant nutrients, although it might carry a significant amount of anthropogeneous pollutants. The extent to which plants react to drought, as well as how pollutants are taken up or how they act on plants, might depend on rhizosphere processes such as mycorrhizal symbioses. Therefore, it seemed timely to investigate plant defense reactions in the presence of arbuscular mycorrhizal fungi (AMF) toward a possible dangerous sewage sludge pollutant under the influence of drought.     

Latex proteins from the plant Calotropis procera are partially digested upon in vitro enzymatic action and are not immunologically detected in fecal material

Soluble proteins from the latex of Calotropis procera (LP) were investigated in vitro and in vivo for digestibility as the latex has previously been shown to produce considerable toxic effects on animals. The latex is also an important biologically active compound that displays antiinflammatory and antidiarrhea properties. The proteins were digested by the action of trypsin, pepsin or chemotrypsin as revealed by gel filtration and SDS-PAGE analysis. Furthermore, the full LP digestion was easily achieved by protease treatment. Rabbit polyclonal antibodies raised against LP failed to detect cross-reactive molecules in fecal material of experimental rats following 35 consecutive days of LP consumption in water. Similar patterns of electrophoresis were observed for the negligible amounts of protein observed in the fecal extracts of control and test animals. No death or toxic effects were observed among animals. Taken together these results suggest that harmful and toxic effects on animals of the latex from C. procera are present in its rubber and low molecular weight fractions rather than its protein content.     

A mathematical model linking tree sap flow dynamics to daily stem diameter fluctuations and radial stem growth

To date, models for simulating sap flow dynamics in individual trees with a direct link to stem diameter variation include only the diameter fluctuation driven by a change in stem water storage. This paper reports results obtained with a comprehensive flow and storage model using whole-tree leaf transpiration as the only input variable. The model includes radial stem growth based on Lockhart's equation for irreversible cell expansion. It was demonstrated that including growth is essential to obtaining good simulation results. To model sap flow dynamics, capacitance of storage tissues was assumed either constant (i.e., electrical analogue approach) or variable and dependent on the water content of the respective storage tissue (i.e., hydraulic system approach). These approaches resulted in different shapes for the desorption curve used to calculate the capacitance of storage tissues. Comparison of these methods allowed detection of specific differences in model simulation of sap flow at the stem base (F(stem)) and stem diameter variation (D). Sensitivity analysis was performed to select a limited subset of identifiable parameters driving most of the variability in model predictions of F(stem) and D Both the electrical analogue and the hydraulic system approach for the flow and storage model were successfully calibrated and validated for the case of a young beech tree (Fagus sylvatica L.). Use of an objective model selection criterion revealed that the flow and storage model based on the electrical analogue approach yielded better predictions.     

Vigor-controlling rootstocks affect early shoot growth and leaf area development of kiwifruit

Patterns of shoot development and the production of different types of shoots were compared with scion leaf area index (LAI) to identify how eight clonal Actinidia rootstocks influence scion development. Rootstocks selected from seven Actinidia species (A. chrysantha Merri., A. deliciosa (A. Chev.) C. F. Liang et A.R. Ferguson, A. eriantha Benth., A. hemsleyana Dunn, A. kolomikta (Maxim. et Rupr.) Maxim., A. kolomikta C.F. Liang and A. polygama (Sieb. et Zucc.) Maxim.) were grafted with the scion Actinidia chinensis Planch. var. chinensis 'Hort16A' (yellow kiwifruit). Based on an earlier architectural analysis of A. chinensis, axillary shoot types produced by the scion were classified as short, medium or long. Short and medium shoots produced a restricted number of preformed leaves before the shoot apex ceased growth and aborted, resulting in a 'terminated' shoot. The apex of long shoots continued growth and produced more nodes throughout the growing seasons. Mid-season LAI of the scion was related to the proportion of shoots that ceased growth early in the season. Scions on low-vigor rootstocks had 50% or less leaf area than scions on the most vigorous rootstocks and had a higher proportion of short and medium shoots. On low-vigor rootstocks, a higher proportion of short shoots was retained during pruning to form the parent structure of the following year. Short parent shoots produced a higher proportion of short daughter shoots than long parent shoots, thus reinforcing the effect of the low-vigor rootstocks. However, overall effects of rootstock on shoot development were consistent regardless of parent shoot type and nodal position within the parent shoot. Slower-growing shoots were more likely to terminate and scions on low-vigor rootstocks produced a higher proportion of slow-growing shoots. Shoot termination also occurred earlier on low-vigor rootstocks. The slower growth of terminating shoots was detectable from about 20 days after bud burst. Removal of a proportion of shoots at the end of bud burst increased the growth rate and decreased the frequency of termination of the remaining shoots on all rootstocks, indicating that the fate of a shoot was linked to competitive interactions among shoots during initial growth immediately after bud burst. Rootstock influenced the process of shoot termination independently of its effect on final leaf size. Scions on low-vigor rootstocks had a higher proportion of short shoots and short shoots on all rootstocks had smaller final leaf sizes at equivalent nodes than medium or long shoots. Only later in the development of long shoots was final leaf size directly related to rootstock, with smaller leaves on low-vigor rootstocks. Thus, the most important effect of these Actinidia rootstocks on scion development occurred during the initial period of shoot growth immediately after bud burst.