Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Development of an in vitro living cell-based model of the intestine that mimics the mechanical, structural, absorptive, transport and pathophysiological properties of the human gut along with its crucial microbial symbionts could accelerate pharmaceutical development, and potentially replace animal testing. Here, we describe a biomimetic ‘human gut-on-a-chip’ microdevice composed of two microfluidic channels separated by a porous flexible membrane coated with extracellular matrix (ECM) and lined by human intestinal epithelial (Caco-2) cells that mimics the complex structure and physiology of living intestine. The gut microenvironment is recreated by flowing fluid at a low rate (30 μL h−1) producing low shear stress (0.02 dyne cm−2) over the microchannels, and by exerting cyclic strain (10%; 0.15 Hz) that mimics physiological peristaltic motions. Under these conditions, a columnar epithelium develops that polarizes rapidly, spontaneously grows into folds that recapitulate the structure of intestinal villi, and forms a high integrity barrier to small molecules that better mimics whole intestine than cells in cultured in static Transwell models. In addition, a normal intestinal microbe (Lactobacillus rhamnosus GG) can be successfully co-cultured for extended periods (>1 week) on the luminal surface of the cultured epithelium without compromising epithelial cell viability, and this actually improves barrier function as previously observed in humans. Thus, this gut-on-a-chip recapitulates multiple dynamic physical and functional features of human intestine that are critical for its function within a controlled microfluidic environment that is amenable for transport, absorption, and toxicity studies, and hence it should have great value for drug testing as well as development of novel intestinal disease models.

Human gut-on-a-chip inhabited by microbial flora that experiences intestinal peristalsis-like motions and flow

1. Clarification: The 2013 Guidelines make a distinction between euthanasia, humane killing, and slaughter, and state that neither slaughter nor humane killing is covered in the document P.68, S6.1.1. Not included among the definitions of these terms are ending the lives of healthy animals or scientific collection of animals. For clarification, whatever the term used, classification of the method, or reason given for killing animals: euthanasia, humane killing, slaughter, harvest, depopulation, scientific collection, or research-related, the Council on Accreditation’s foremost concern, in all situations, is with humane technique. The goal of humane technique is to minimize pain, distress, and the negative effect to the animal. The technique employed should result in rapid loss of consciousness followed by cardiac or respiratory arrest and, ultimately, a loss of brain function. Although complete absence of pain and distress is preferred, it is understood that it cannot always be achieved P7.13.2.

https://works.bepress.com/cheryl_greenacre/14/download/

AVMA Guidelines for the Euthanasia of Animals: 2013 Edition

Many investigators use the reduced major axis (RMA) instead of ordinary least squares (OLS) to define a line of best fit for a bivariate relationship when the variable represented on the X-axis is measured with error. OLS frequently is described as requiring the assumption that X is measured without error while RMA incorporates an assumption that there is error in X. Although an RMA fit actually involves a very specific pattern of error variance, investigators have prioritized the presence versus the absence of error rather than the pattern of error in selecting between the two methods. Another difference between RMA and OLS is that RMA is symmetric, meaning that a single line defines the bivariate relationship, regardless of which variable is X and which is Y, while OLS is asymmetric, so that the slope and resulting interpretation of the data are changed when the variables assigned to X and Y are reversed. The concept of error is reviewed and expanded from previous discussions, and it is argued that the symmetry-asymmetry issue should be the criterion by which investigators choose between RMA and OLS. This is a biological question about the relationship between variables. It is determined by the investigator, not dictated by the pattern of error in the data. If X is measured with error but OLS should be used because the biological question is asymmetric, there are several methods available for adjusting the OLS slope to reflect the bias due to error. RMA is being used in many analyses for which OLS would be more appropriate.

Use and misuse of the reduced major axis for line-fitting

Common to liquids, solids and substances in between the former two is that if a stress is applied to them, they will strain. Stress may be visualized by placing a small amount of fluid between two parallel plates. When one plate slides over the other, forces act on the fluid dependent upon the rate of the plate movement. This causes a shear stress on the liquid. Recall laminar flow of fluids through a tubular vessel. Strain is the response to the stress. If solids are elastic, they deform and return to their original shape. Since fluids are not elastic and, hence, viscous, their deformation is irreversible.

Introduction to rheology

This review highlights the limited amount of research conducted regarding the optimum particle size of different feeds for efficient poultry production. The current industry practice of using highl...

Feed particle size: Implications on the digestion and performance of poultry

The physical properties of digesta may influence mixing, efficiency of digestion, and absorption within the lumen of the intestine. We review how the physical properties of digesta change during transit through the various segments of the intestine, and how their influence on flow and mixing may be modulated by peristaltic activity. We examine how, in more fluid digesta, the solid and liquid phases interact to influence flow and mixing. Similarly, how in viscid digesta, shear strength, plasticity and elasticity of contained particulate material may influence the permeation of the fluid phase and secretions into and out of the digesta bolus. The manner in which the solid and liquid phases of digesta interact in a partly gaseous environment, such as the lower bowel, to influence bolus cohesion is also examined. Those mechanisms that promote the formation of a less viscous layer at the mucosal interface to promote plug flow are reviewed, and their effect on the efficiency of mixing and digestion discussed. It is recommended that in any future work investigating the character of mixing in the intestine, a wider range of appropriate digesta properties be measured and that, in investigations of intestinal movement, perfusates with similar characteristics to digesta be used.

Physical characteristics of digesta and their influence on flow and mixing in the mammalian intestine: a review

Influence of Feed Particle Size and Feed Form on the Performance, Energy Utilization, Digestive Tract Development, and Digesta Parameters of Broiler Starters

1. An experiment of 21-d duration was conducted to examine the effects of diluting wheat-based diets with insoluble fibre sources and whole wheat inclusion on the performance, nutrient utilisation, digestive tract development and ileal microbiota profile of broiler chickens. The treatments were as follows: Treatment 1, control diet based on ground wheat; Treatment 2, where 200 g/kg whole wheat replaced the ground wheat pre-pelleting; and Treatments 3 and 4 where the control diet was diluted with fine cellulose and wood shavings, respectively, at a ratio of 6 : 100 (w/w). 2. Weight gains and apparent metabolisable energy were unaffected by dietary treatment. Gain : feed ratio was not influenced by the inclusion of whole wheat or wood shavings, but decreased with cellulose inclusion. However, when gain:feed of birds was corrected by subtracting the amount of cellulose and wood shavings from the total feed consumption, it was found that the inclusion of wood shavings increased gain : feed, while cellulose inclusion had no effect. Similarly, AME(N) was unaffected by dietary treatment. However, when AME(N) was corrected for energy contribution from cellulose or wood shavings, improvements in AME(N) were observed in these two treatments. 3. Wood shavings increased the relative gizzard weights and improved ileal starch digestibility compared to other dietary treatments. All gut components were shorter in birds given diets containing cellulose and wood shavings compared to those receiving the control and whole wheat diets. 4. Ileal microbiota profiling, using denaturing gradient gel electrophoresis, showed that microbial composition was affected by dietary treatment and that the treatments were grouped into two main clusters. The two groupings showed similarity between birds receiving the control and cellulose diets and similarity between birds fed on the whole wheat and wood shavings diets. 5. The findings suggest that the effects of insoluble fibre on broiler performance differed depending on the fibre particle size.

Influence of insoluble fibre and whole wheat inclusion on the performance, digestive tract development and ileal microbiota profile of broiler chickens

Influence of Feed Particle Size on the Performance, Energy Utilization, Digestive Tract Development, and Digesta Parameters of Broiler Starters Fed Wheat- and Corn-Based Diets

Roger G. Lentle

Papers

Feed particle size: Implications on the digestion and performance of poultry

Physical characteristics of digesta and their influence on flow and mixing in the mammalian intestine: a review

Influence of Feed Particle Size and Feed Form on the Performance, Energy Utilization, Digestive Tract Development, and Digesta Parameters of Broiler Starters

Influence of insoluble fibre and whole wheat inclusion on the performance, digestive tract development and ileal microbiota profile of broiler chickens

Influence of Feed Particle Size on the Performance, Energy Utilization, Digestive Tract Development, and Digesta Parameters of Broiler Starters Fed Wheat- and Corn-Based Diets