Using simple models to review the application and implications of different approaches used to simulate transmission of pathogens among aquatic animals

Disease is an important issue affecting aquatic animal populations. Aquatic pathogens may be transmitted in ways that could result in qualitatively different impacts to those of terrestrial diseases. I analyse simple SIR epidemic models with different functions to describe transmission. Four forms of transmission are applied: density-dependent, density-independent, non-linear density-dependent and constant infection pressure; the first two are similar to terrestrial systems, the second two are based on specifically aquatic modes of transmission. Observed diseases and existing models are reviewed in terms of these simple forms. The significance of mode of transmission to host populations, to strategies to prevent or control diseases, and to wild-farm interactions are analysed. Different diseases are simulated by different transmission models, for example furunculosis depends on host density, while spread of phocine distemper virus is density-independent, and sea lice infestation pressure may result from open transmission processes that are not dependent on local infested hosts. Appropriate transmission model may also depend on the scale of interest (inter- or intra-population). These different models result in very different responses to intervention strategies, for example culling may be effective for controlling density-dependent disease but may be counter-productive when pathogens depend on open recruitment. It is therefore important for management that appropriate models (whether existing or novel) be selected and this paper aims to provide a basic framework for cataloguing and management of aquatic diseases.     

Regulation of protein metabolism by insulin: value of different approaches and animal models

Insulin induces protein accretion by stimulating protein synthesis and inhibiting proteolysis. However, the mechanisms of regulation of protein metabolism by insulin are complex and still not completely understood. The use of approaches combining hyperinsulinemic clamp and isotopic methods, or measurement of the activation of intracellular kinases involved in insulin signaling, in addition to the use of different animal models in a comparative physiology process, provide better understanding of the potential regulation of protein metabolism by insulin. Studies using the clamp technique in lactating goats have shown a clear inhibitory effect of insulin on proteolysis, with an interaction between the effects of insulin and amino acids. Such studies revealed that the insulin-inhibited proteolysis is improved in lactating goats, this adaptative process limiting the mobilization of body protein under the conditions of amino acid deficit which occurs during early lactation. Insulin signaling studies in growing chickens have also provided some interesting features of insulin regulation compared to mammals. Refeeding or insulin injection leads to the activation of the early steps of insulin receptor signaling in the liver but not in the muscle. Muscle p70 S6 kinase, a kinase involved in the insulin activation of protein synthesis, was found to be markedly activated in response to insulin and to refeeding, suggesting that other signaling pathways than those classically described in mammalian muscles may be involved in signal transduction. Finally, although the role of insulin has been doubtful and has long been considered to be minor in ruminants and in avian species, this hormone clearly regulates protein metabolism in both species.     

Problem-solving concepts and theories

Many educators, especially those involved in professional curricula, are interested in problem solving and in how to support students' development into successful problem solvers. The following article serves as an overview of educational research on problem solving. Several concepts are defined and the transition from one theory to another is discussed. Educational theories describing problem solving in the context of behavioral, cognitive, and information-processing pedagogy are discussed. The final section of the article describes prior findings regarding expert-novice differences in problem solving of various kinds.     

Nutritional approaches to slow late finishing pig growth: implications on carcass composition and pork quality

Although pork producers typically aim to optimize growth rates, occasionally it is necessary to slow growth, such as when harvest facility capacity is limited. In finishing pigs, numerous dietary strategies can be used to slow growth so pigs are at optimal slaughter body weights when harvest facility capacity and/or access is restored. However, the impact of these diets on pork carcass quality is largely unknown. Thus, this study aimed to evaluate the efficacy of dietary strategies to slow growth in late finishing pigs and evaluate their effects on carcass composition and pork quality. Mixed-sex pigs (n = 897; 125 ± 2 kg BW) were randomly allotted across 48 pens and assigned to 1 of 6 dietary treatments (n = 8 pens/treatment): (1) Control diet representative of a typical finisher diet (CON); (2) diet containing 3% calcium chloride (CaCl₂); (3) diet containing 97% corn and no soybean meal (Corn); (4) diet deficient in isoleucine (LowIle); (5) diet containing 15% neutral detergent fiber (NDF) from soybean hulls (15% NDF); and (6) diet containing 20% NDF from soybean hulls (20% NDF). Over 42 d, pen body weights and feed disappearance were collected. Pigs were harvested in 3 groups (14, 28, and 42 d on feed) and carcass data collected. From the harvest group, 1 loin was collected from 120 randomly selected carcasses (20 loins/treatment) to evaluate pork quality traits. Overall, ADG was reduced in CaCl₂, Corn, and 20% NDF pigs compared with CON pigs (P < 0.001). However, ADFI was only reduced in CaCl₂ and 20% NDF pigs compared with CON (P < 0.001). Feed efficiency was reduced in CaCl₂ and Corn pigs compared with CON (P < 0.001). Hot carcass weights were reduced in CaCl₂ pigs at all harvest dates (P < 0.001) and were reduced in Corn and 20% NDF pigs at days 28 and 42 compared with CON pigs (P < 0.001). In general, CaCl₂ and 20% NDF diets resulted in leaner carcasses, whereas the Corn diet increased backfat by 42 d on test (P < 0.05). Loin pH was reduced and star probe increased in CaCl₂ pigs compared with CON pigs (P < 0.05); no treatments differed from CON pigs regarding drip loss, cook loss, color, firmness, or marbling (P ≥ 0.117). Overall, these data indicate that several dietary strategies can slow finishing pig growth without evidence of behavioral vices. However, changes to carcass composition and quality were also observed, indicating quality should be taken into consideration when choosing diets to slow growth.     

Impact of different approaches to calculate the economics of disease in pig farming

Diagrams for analyzing the economics of sow and fattening farms are described and discussed. The diagrams are used to quantify the economic significance of a change in technical results for pig farms in the Netherlands. Sensitivity analyses show the importance of taking into account feed savings of piglets and sows due to, for instance, less litters per sow per year. To see whether there was an effect of the economic environment and the structure of the fanning system, the same calculations were carried out for Minnesota (USA). The economic effect of a change in results (e.g. days open) was smaller for Minnesota, but economic effects were similarly influenced by specific factors, such as feed intake and price. Subsequently, several scientific publications on the estimation of the costs of Aujeszky's disease in pigs were compared with respect to the economic methods used and the outcomes obtained. Because of different estimation procedures, the costs of the disease varied significantly. Differences are mainly due to the loss items that were taken into account, the way the loss items were calculated and the structure of the farming system that was included. There is a need for a standardized framework of how to conduct a sound economic evaluation, in order to make the outcome of different calculations more comparable and interpretable.     

Analyzing the effect of different approaches of penalized relationship in multistage selection schemes

The aim of this study was to extend optimum contribution selection to more realistic breeding schemes with multistage selection. It seems that if the last selection stage accounts for the relationship of the selected animals, then previous selection stages also account for this relationship. An extreme example was considered here: the preselection of dairy bulls that enter a progeny testing scheme. First the penalty on the average relationship in selection step 1 is assumed the same as in step 2. Thereafter, situations with different penalties on the average relationship in the 2 selection steps were analyzed. The simulation started with the generation of prior EBV, which were sampled from a truncated normal distribution. Possible candidates for further progeny testing were selected and progeny test EBV were simulated, where the progeny test was based on 100 daughters per young bull. In situations with greater accuracy of prior EBV, high trait heritability and prior EBV were available for 2,000 bulls; the results were similar for both approaches, independent of family size. However, in a situation with low accuracy of prior EBV and low trait heritability it could be observed that with increasing penalty on the average relationship, correction for relationship in stage 1 yielded in a similar genetic level compared with selecting only for high prior EBV. If the number of bulls with prior EBV increased from 2,000 to 4,000, an increasing penalty on an average relationship gave an improved genetic level. A further improvement of the results with respect to genetic level and average relationship could be observed by increasing the penalty on an average relationship in selection step 1 above that in selection step 2. Overall, this study showed that it is beneficial to use a penalty on an average relationship already for the selection of bulls that enter the progeny test. In case optimum contribution was applied with a constraint on the average relationship in stage 2, this constraint may be translated into a penalty on the average relationship, and the current results suggested that the optimal penalty in selection stage 1 should be twice that of stage 2.     

Calculation of utilizable crude protein at the duodenum of cattle by two different approaches.

The duodenal flow of utilizable crude protein (crude protein minus endogenous protein) in cows was estimated using dietary parameters, first by multiple regression and secondly by the addition of microbial protein and undegraded feed protein. These estimates were compared with 327 results from experiments conducted with fistulated cows in Braunschweig-V?lkenrode and Rostock-Dummerstorf. The regressions and the measurements for microbial protein synthesis as well as feed protein degradation and organic matter fermentation in the rumen were based on the same experimental data set. The prediction of utilizable crude protein (uCP) at the duodenum by regression with digested organic matter (kg DOM) and undegraded feed protein (g UDP) as predicting variables, was more accurate than the value given by microbial protein synthesis and rumen protein degradability. The regression model [g uCP = [188.5-(116.5 (UDP/CP))] DOM + 1.03 UDP] had the highest coefficient of determination (r2 = 0.91) and the lowest coefficient of variation (cv = 8.6); indicating the model's superiority over the other method of estimation.     

Prenatal development of the caudal vena cava in mammals: review of the different theories with special reference to the dog

Several items of the development of the caudal vena cava in domestic animals are still controversial. In particular, the origin of the lumbar segment of the caudal vena cava is equivocally described. According to different theories it originates from the right-sided supracardinal, caudal cardinal, sacrocardinal, lateral sympathetic or subcardinal veins. In this review, all five theories are compared with each other and discussed in the light of anatomical variations observed in eight dogs. Species-specific diversity, erratic observations because of technical artefacts, and biased interpretation of the original data are three major reasons for the dissimilarity between the five theories, but they cannot explain all differences. Further studies by using modern techniques such as microvascular corrosion casting and non-invasive three-dimensional microtomography are necessary to better understand the normal development and to explain the variations in domestic animal species.     

孔子的素质教育思想及其现实意义

孔子的教育思想是中华民族传统教育思想体系中的宝贵遗产。其教育思想与当前素质教育有很多相通之处,所以对孔子的教育思想进行解读将对我们教育实践的指导和教育理论水平的提高将大有裨益。以《论语》中孔子的言论为原材料,以他对老师和学生的要求以及如何处理师生关系这三方面为切入点浅析孔子的教育思想对现代素质教育的启示与影响。