The effect of meal composition on specific dynamic action in burmese pythons (Python molurus)

We quantified the specific dynamic action (SDA) resulting from the ingestion of various meal types in Burmese pythons (Python molurus) at 30 degrees C. Each snake was fed a series of experimental meals consisting of amino acid mixtures, simple proteins, simple or complex carbohydrates, or lipids as well as meals of whole animal tissue (chicken breast, beef suet, and mouse). Rates of oxygen consumption were measured for approximately 4 d after feeding, and the increment above standard metabolic rate was determined and compared to energy content of the meals. While food type (protein, carbohydrate, and lipid) had a general influence, SDA was highly dependent on meal composition (i.e., amino acid composition and carbohydrate structure). For chicken breast and simple carbohydrates, the SDA coefficient was approximately one-third the energetic content of the meal. Lard, suet, cellulose, and starch were not digested and did not produce measurable SDA. We conclude that the cost of de novo protein synthesis is an important component of SDA after ingestion of protein meals because (1) simple proteins, such as gelatin and collagen, did not stimulate levels of SDA attained after consumption of complete protein, (2) incomplete mixtures of amino acids failed to elicit the SDA of a complete mixture, and (3) the inhibition of de novo protein synthesis with the drug cycloheximide caused a more than 70% decrease in SDA. Stomach distension and mechanical digestion of intact prey did not cause measurable SDA.     

Gamma-Ray Sterilization and Residual Toxicity Studies of Ground Beef Inoculated with Spores of Clostridium botulinum

Inoculated packs of cooked and raw ground beef were sterilized with gamma radiation from cobalt-60. With inocula of 5,000,000 Clostridium botulinum 213B spores per g of cooked ground beef, 3.8 megarad were required for sterilization; in raw ground beef, 3.72 megarad sterilized the meat when inocula of 1,700,000 C. botulinum 213B spores were used per g. Using C. botulinum 62A spores, cooked ground beef inoculated with 5,200,000 spores per g was sterilized with 3.85 megarad; raw ground beef, inoculated with 2,670,000 spores per g, was sterilized with 3.6 megarad. Cans of meat that were considered sterile by lack of culture growth after incubation for at least 6 months and, in some instances, as long as 5 years, were tested for the presence of botulinus toxin. No toxin was found in any meat taken from inoculated packs prepared from C. botulinum 213B spores; however, all cans of meat that had been inoculated with more than 2,670,000 C. botulinum 62A spores per g of meat, contained type A toxin. It was shown that these latter inocula of heat-shocked spores, by themselves, contained sufficient toxin to kill mice. However, more toxin appeared to be present than could be ascribed to the unirradiated spores alone. This finding is discussed.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

Specific dynamic action: a review of the postprandial metabolic response

For more than 200 years, the metabolic response that accompanies meal digestion has been characterized, theorized, and experimentally studied. Historically labeled “specific dynamic action” or “SDA”, this physiological phenomenon represents the energy expended on all activities of the body incidental to the ingestion, digestion, absorption, and assimilation of a meal. Specific dynamic action or a component of postprandial metabolism has been quantified for more than 250 invertebrate and vertebrate species. Characteristic among all of these species is a rapid postprandial increase in metabolic rate that upon peaking returns more slowly to prefeeding levels. The average maximum increase in metabolic rate stemming from digestion ranges from a modest 25% for humans to 136% for fishes, and to an impressive 687% for snakes. The type, size, composition, and temperature of the meal, as well as body size, body composition, and several environmental factors (e.g., ambient temperature and gas concentration) can each significantly impact the magnitude and duration of the SDA response. Meals that are large, intact or possess a tough exoskeleton require more digestive effort and thus generate a larger SDA than small, fragmented, or soft-bodied meals. Differences in the individual effort of preabsorptive (e.g., swallowing, gastric breakdown, and intestinal transport) and postabsorptive (e.g., catabolism and synthesis) events underlie much of the variation in SDA. Specific dynamic action is an integral part of an organism’s energy budget, exemplified by accounting for 19–43% of the daily energy expenditure of free-ranging snakes. There are innumerable opportunities for research in SDA including coverage of unexplored taxa, investigating the underlying sources, determinants, and the central control of postprandial metabolism, and examining the integration of SDA across other physiological systems.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis.

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Impact of meat consumption, preparation, and mutagens on aggressive prostate cancer

Background

The association between meat consumption and prostate cancer remains unclear, perhaps reflecting heterogeneity in the types of tumors studied and the method of meat preparation—which can impact the production of carcinogens.

Methods

We address both issues in this case-control study focused on aggressive prostate cancer (470 cases and 512 controls), where men reported not only their meat intake but also their meat preparation and doneness level on a semi-quantitative food-frequency questionnaire. Associations between overall and grilled meat consumption, doneness level, ensuing carcinogens and aggressive prostate cancer were assessed using multivariate logistic regression.

Results

Higher consumption of any ground beef or processed meats were positively associated with aggressive prostate cancer, with ground beef showing the strongest association (OR = 2.30, 95% CI:1.39–3.81; P-trend = 0.002). This association primarily reflected intake of grilled or barbequed meat, with more well-done meat conferring a higher risk of aggressive prostate cancer. Comparing high and low consumptions of well/very well cooked ground beef to no consumption gave OR''s of 2.04 (95% CI:1.41–2.96) and 1.51 (95% CI:1.06–2.14), respectively. In contrast, consumption of rare/medium cooked ground beef was not associated with aggressive prostate cancer. Looking at meat mutagens produced by cooking at high temperatures, we detected an increased risk with 2-amino-3,8-Dimethylimidazo-[4,5-f]Quinolaxine (MelQx) and 2-amino-3,4,8-trimethylimidazo(4,5-f)qunioxaline (DiMelQx), when comparing the highest to lowest quartiles of intake: OR = 1.69 (95% CI:1.08–2.64;P-trend = 0.02) and OR = 1.53 (95% CI:1.00–2.35; P-trend = 0.005), respectively.

Discussion

Higher intake of well-done grilled or barbequed red meat and ensuing carcinogens could increase the risk of aggressive prostate cancer.     

Fecal mutagenicity arising from ingestion of fried ground beef in the human

Fried ground beef has been shown to contain mutagens, and the major mutagenic component has been identified as 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). Mutagens in feces of 3 adult volunteers were fractionated by treatment of the feces with blue cotton followed by chromatography on a carboxymethyl cellulose column. The chromatographic fraction, corresponding to MeIQx in terms of the position of elution, was examined for mutagenicity in S. typhimurium TA98 with metabolic activation. When meals containing no heated meat were eaten, this fraction of feces showed little or no mutagenicity. On eating fried ground beef, the feces excreted in the next two days showed greatly increased mutagenicity in this fraction. By eating no-meat meal subsequent to the meat meal, the mutagenicity resumed the original low level on the fourth day after the meat meal. The components in the mutagenic fraction were probably metabolites of the mutagens present in cooked meat, since analysis by high pressure liquid chromatography of the mutagenic fraction showed that the active components in the feces were different from the mutagens in cooked meat.     

The effect of temperature on the formation of mutagens in heated beef stock and cooked ground beef

The microsome-activatable mutagens (chromatographically distinguishable from benzo[a]pyrene and from the mutagens produced from pyrolysed amino acids and proteins) previously found in beef extract and in bacterial nutrients which contain beef extract are produced when beef stock is heated. Reflux boiling of beef stock at 100°C results in a linear increase in mutagenic activity toward Salmonella strain TA1538. The rate of production of mutagenic activity at temperatures between 68°C and 98°C conforms closely to the Arrhenius equation, yielding an activation energy of 23 738 calories per mole. Extrapolation from these data predicts a sharp rise in the rate of mutagen formation between 140 and 180°C. This expectation is confirmed when ground beef patties (hamburgers) are prepared in various conventional electrically-heated appliances which operate at different cooking temperatures within this range. The mutagenic activity of hamburger cooked at high temperatures is limited to the surface layers; the temperature of the inside of the hamburger does not exceed 100°C during cooking. No mutagenic activity is found in comparable samples of uncooked meat. The results indicated that the mutagens may be formed as a result of the temperatures encountered in certain conventional cooking procedures.     

Effects of carcass maturity on meat quality characteristics of beef semitendinosus muscle for chinese native yellow steers

This work was designed to study the effects of carcass maturity on meat quality characteristics and intramuscular connective tissue of beef semitendinosus muscle from Chinese native Yellow steers. Chemical determinations, histological and mechanical measurements were performed on the raw and cooked meat at 4 days post mortem. In raw meat, intramuscular fat, collagen solubility, mechanical strength and transition temperature of intramuscular connective tissue increased (P < 0.05) with carcass maturity before body maturation, whilst moisture, total collagen, fibre diameter decreased after body maturation. Warner-Bratzlar shear force (WBSF) of cooked meat increased with maturity before body maturation due to the muscle atrophy, and thus the decline of moisture content and the increase of cooking losses. After body maturation, the increase of WBSF was neutralised by the increase of intramuscular fat, the decrease of total collagen and the elongation of sarcomere length.     

Specific dynamic action of ambystomatid salamanders and the effects of meal size, meal type, and body temperature

The past decade has witnessed a dramatic increase in studies of amphibian and reptile specific dynamic action (SDA). These studies have demonstrated that SDA, the summed energy expended on meal digestion and assimilation, is affected significantly by meal size, meal type, and body size and to some extent by body temperature. While much of this attention has been directed at anuran and reptile SDA, we investigated the effects of meal size, meal type, and body temperature on the postprandial metabolic responses and the SDA of the tiger salamander (Ambystoma tigrinum tigrinum). We also compared the SDA responses among six species of Ambystoma salamanders representing the breadth of Ambystoma phylogeny. Postprandial peaks in VO(2) and VO(2), duration of elevated metabolism, and SDA of tiger salamanders increased with the size of cricket meals (2.5%-12.5% of body mass). For A. tigrinum, as for other ectotherms, a doubling of meal size results in an approximate doubling of SDA, a function of equal increases in peak VO(2) and duration. For nine meal types of equivalent size (5% of body mass), the digestion of hard-bodied prey (crickets, superworms, mealworms, beetles) generated larger SDA responses than the digestion of soft-bodied prey (redworms, beetle larvae). Body temperature affected the profile of postprandial metabolism, increasing the peak and shortening the duration of the profile as body temperature increased. SDA was equivalent among three body temperatures (20 degrees, 25 degrees, and 30 degrees C) but decreased significantly at 15 degrees C. Comparatively, the postprandial metabolic responses and SDA of Ambystoma jeffersonianum, Ambystoma maculatum, Ambystoma opacum, Ambystoma talpoideum, Ambystoma texanum, and the conspecific Ambystoma tigrinum mavortium digesting cricket meals that were 5% of their body mass were similar (independent of body mass) to those of A. t. tigrinum. Among the six species, standard metabolic rate, peak postprandial VO(2), and SDA scaled with body mass with mass exponents of 0.72, 0.78, and 1.05, respectively.     

The effects of meal size on postprandial metabolic response and post-exercise metabolic recovery process in juvenile black carp (Mylopharyngodon piceus)

The effects of meal size on the postprandial metabolic response and of digestion on the post-exercise metabolic recovery process were investigated in juvenile black carp (Mylopharyngodon piceus) . Experimental fish were forcedly fed with compound feed (meal sizes: 0.5%, 1% and 2% body weight). Then, the postprandial oxygen consumption rate and excess post-exercise oxygen consumption (EPOC) of the experimental fish were measured. Both the duration and the peak of oxygen consumption rate (PMR) increased with increasing meal size. The peak post-exercise metabolic rate of digesting fish were significantly higher, whereas EPOC magnitude and its duration were significantly smaller or (shorter) than those in the fasting fish. It is suggested that (1) this fish fulfills the increased energy demand during the digestive process by increasing PMR and by prolonging SDA duration with increasing meal size and (2) digesting fish might decrease their anaerobic exhaustive activity but increase the post-exercise recovery capacity.     

Effects of ration size and hypoxia on specific dynamic action in the cod

We present the first data on the effect of hypoxia on the specific dynamic action (SDA) in a teleost fish. Juvenile cod (Gadus morhua) were fed meals of 2.5% and 5% of their wet body mass (BM) in normoxia (19.8 kPa Po(2)) and 5% BM in hypoxia (6.3 kPa Po(2)). Reduced O(2) availability depressed the postprandial peaks of oxygen consumption, and to compensate for this, the total SDA duration lasted 212.0+/-20 h in hypoxia, compared with 95.1+/-25 h in normoxia. The percentage of energy associated with the meal digestion and assimilation (SDA coefficient) was equivalent between the different feeding rations but higher for fish exposed to hypoxia. Comparing peak oxygen consumption during the SDA course with maximum metabolic rates showed that food rations of 2.5% and 5% BM reduced the scope for activity by 40% and 55%, while ingestion of 5% BM in hypoxia occupied 69% of the aerobic scope, leaving little energy for other activities.     

Effects of body mass, meal size, fast length, and temperature on specific dynamic action in the timber rattlesnake (Crotalus horridus)

Detailed analysis of animal energy budgets requires information on the cost of digestion (specific dynamic action [SDA]), which can represent a significant proportion of ingested energy (up to 30% in infrequent feeders). We studied the effects of snake mass, temperature (25 degrees and 30 degrees C), fasting time (1 and 5 mo), and prey size (10%-50% of snake mass) on SDA in 26 timber rattlesnakes (Crotalus horridus). We used flow-through respirometry to measure hourly CO(2) production rates (VCO2) for 1 d before and up to 17 d after feeding. Crotalus horridus, like previously studied viperids and boids, show large and ecologically relevant increases in metabolism due to feeding. Depending on treatment and individual, VCO2 increased to 2.8-11.8 times the resting metabolic rate within 12-45 h postfeeding and decreased to baseline within 4.3-15.4 d. Significant effects of snake mass, meal mass, and fast length were detected. Increased temperature decreased the time required to complete the process but had little effect on total energy expended on SDA. Energy expended on SDA increased with increasing fast length, snake mass, and prey mass. Considering all of our data, we found that a simple allometric relationship explained 96.7% of the variation in total CO(2) production during SDA. Calculations suggest that energy devoted to SDA may approach 20% of the total annual energy budget of snakes in nature. Discrepancies between our data and some previous studies draw attention to the fact that the measurement, expression, and analysis of SDA may be sensitive to several methodological and statistical assumptions.     

Oxygen consumption and the energetics of island-dwelling Florida cottonmouth snakes

We measured oxygen consumption (Vo(2)) to estimate standard metabolic rates (SMR) in cottonmouth snakes (Agkistrodon piscivorus conanti) from Seahorse Key and the adjacent peninsula of northern Florida. The island population is unusual because adult snakes feed on fish that are dropped by colonial nesting birds, and food resources are temporally limited relative to that of mainland populations. We found no differences in SMR between island and mainland snakes at any of four experimental temperatures (15 degrees -30 degrees C), suggesting that any adjustments to energy limitations involve other aspects of physiology or behavior. As with other viperid species, the SMR of cottonmouths is about one-half of that expected from interspecific allometric regressions previously reported for snakes generally. Allometric mass exponents of SMR averaged 0.76 and were not affected by temperature. We found that Vo(2) increased with temperature (Q(10) = 2.4-2.8) and was elevated 29% during scotophase compared with photophase. Neonates exhibited elevated Vo(2)compared with older juveniles of similar size, apparently due to assimilation of yolk that is present in the neonatal gut. In adult snakes, specific dynamic action (SDA) following feeding resulted in four- to eightfold increases in Vo(2), with magnitude and duration related positively to relative meal size. The total energy devoted to SDA increased with meal size and averaged 32.8%+/-4.4% of total ingested energy. We estimate that a nonreproductive 500-g adult cottonmouth at Seahorse Key uses 3,656 kJ of assimilated energy annually for maintenance and activity, which requires ingestion of approximately 1 kg of fish.     

The respiratory consequences of feeding in amphibians and reptiles

Many ectothermic vertebrates ingest very large meals at infrequent intervals. The digestive processes associated with these meals, often coupled with an extensive hypertrophy of the gastrointestinal organs, are energetically expensive and metabolic rate, therefore, increases substantially after feeding (specific dynamic action, SDA). Here, we review the cardio-respiratory consequences of SDA in amphibians and reptiles. For some snakes, the increased oxygen uptake during SDA is of similar magnitude to that of muscular exercise, and the two physiological states, therefore, exert similar and profound demands on oxygen transport by the cardiorespiratory systems. In several species, SDA is attended by increases in heart rate and overall systemic blood flows, but changes in blood flow distribution remain to be investigated. In snakes, the regulation of heart rate appears to involve a non-adrenergic-non-cholinergic mechanism, which may be a regulatory peptide released from the gastrointestinal system during digestion. Digestion is also associated with a net acid secretion to the stomach that causes an increase in plasma HCO3- concentration (the 'alkaline tide'). Experiments on chronically cannulated amphibians and reptiles, show that this metabolic alkalosis is countered by an increased P(CO2), so that the change in arterial pH is reduced. This respiratory compensation of arterial pH is accomplished through a reduction in ventilation relative to metabolism, but the estimated reductions in lung P(O2) are relatively small. The SDA response is also associated with haematological changes, but large interspecific differences exist. The studies on cardiorespiratory responses to digestion may allow for a further understanding of the physiological and structural constraints that limits the ability of reptiles and amphibians to sustain high metabolic rates.     

The energetic significance of cooking

While cooking has long been argued to improve the diet, the nature of the improvement has not been well defined. As a result, the evolutionary significance of cooking has variously been proposed as being substantial or relatively trivial. In this paper, we evaluate the hypothesis that an important and consistent effect of cooking food is a rise in its net energy value. The pathways by which cooking influences net energy value differ for starch, protein, and lipid, and we therefore consider plant and animal foods separately. Evidence of compromised physiological performance among individuals on raw diets supports the hypothesis that cooked diets tend to provide energy. Mechanisms contributing to energy being gained from cooking include increased digestibility of starch and protein, reduced costs of digestion for cooked versus raw meat, and reduced energetic costs of detoxification and defence against pathogens. If cooking consistently improves the energetic value of foods through such mechanisms, its evolutionary impact depends partly on the relative energetic benefits of non-thermal processing methods used prior to cooking. We suggest that if non-thermal processing methods such as pounding were used by Lower Palaeolithic Homo, they likely provided an important increase in energy gain over unprocessed raw diets. However, cooking has critical effects not easily achievable by non-thermal processing, including the relatively complete gelatinisation of starch, efficient denaturing of proteins, and killing of food borne pathogens. This means that however sophisticated the non-thermal processing methods were, cooking would have conferred incremental energetic benefits. While much remains to be discovered, we conclude that the adoption of cooking would have led to an important rise in energy availability. For this reason, we predict that cooking had substantial evolutionary significance.     

Pythons metabolize prey to fuel the response to feeding

We investigated the energy source fuelling the post-feeding metabolic upregulation (specific dynamic action, SDA) in pythons (Python regius). Our goal was to distinguish between two alternatives: (i) snakes fuel SDA by metabolizing energy depots from their tissues; or (ii) snakes fuel SDA by metabolizing their prey. To characterize the postprandial response of pythons we used transcutaneous ultrasonography to measure organ-size changes and respirometry to record oxygen consumption. To discriminate unequivocally between the two hypotheses, we enriched mice (= prey) with the stable isotope of carbon (13C). For two weeks after feeding we quantified the CO2 exhaled by pythons and determined its isotopic 13C/12C signature. Ultrasonography and respirometry showed typical postprandial responses in pythons. After feeding, the isotope ratio of the exhaled breath changed rapidly to values that characterized enriched mouse tissue, followed by a very slow change towards less enriched values over a period of two weeks after feeding. We conclude that pythons metabolize their prey to fuel SDA. The slowly declining delta13C values indicate that less enriched tissues (bone, cartilage and collagen) from the mouse become available after several days of digestion.     

Molecular characterization of Escherichia coli O157:H7 recovered from meat and meat products relevant to human health in Riyadh,Saudi Arabia

Raw meat can harbor pathogenic bacteria, potentially harmful to humans such as Escherichia coli O157:H7 causing diarrhea and hemolytic-uremic syndrome (HS). Therefore, the current study was carried out to evaluate the prevalence and the molecular detection characterization of E. coli serotype O157:H7 recovered from raw meat and meat products collected from Saudi Arabia. During the period of 25th January 2013 to 25th March 2014, 370 meat samples were collected from abattoirs and markets located in Riyadh, Saudi Arabia “200 raw meat samples and 170 meat products”. Bacteriological analysis of the meat samples and serotyping of the isolated E. coli revealed the isolation of 11 (2.97%) strains of E. coli O157:H7. Isolation of E. coli O157:H7 in raw beef, chicken and mutton were 2%, 2.5%, and 2.5%, respectively, however, there was no occurrence in raw turkey. The incidences of E. coli O157:H7 in ground beef, beef burgers, beef sausage, ground chicken and chicken burgers were 5%, 10%, 0.0%, 5% and 0.0%, respectively. The multiplex PCR assay revealed that 3 (27.27%) out of 11 E. coli O157:H7 isolates from raw beef, chicken and mutton had stx1, stx2, and eae while 5 (45.45%) E. coli O157:H7 isolates from ground beef, ground chicken, and raw beef had both stx1 and stx2. However, from beef burgers, only one E. coli O157:H7 isolate had stx1 while two were positive for hlyA gene. These results call for urgent attention toward appropriate controls and good hygienic practices in dealing with raw meat.     

The postabsorptive and postprandial metabolic rates of praying mantises: Comparisons across species,body masses,and meal sizes

The metabolic rate of an animal affects the amount of energy available for its growth, activity and reproduction and, ultimately, shapes how energy and nutrients flow through ecosystems. Standard metabolic rate (SMR; when animals are post-absorptive and at rest) and specific dynamic action (SDA; the cost of digesting and processing food) are two major components of animal metabolism. SMR has been studied in hundreds of species of insects, but very little is known about the SMR of praying mantises. We measured the rates of CO₂ production as a proxy for metabolic rate and tested the prediction that the SMR of mantises more closely resembles the low SMR of spiders – a characteristic generally believed to be related to their sit-and-wait foraging strategy. Although few studies have examined SDA in insects we also tested the prediction that mantises would exhibit comparatively large SDA responses characteristic of other types of predators (e.g., snakes) known to consume enormous, protein-rich meals. The SMR of the mantises was positively correlated with body mass and did not differ among the four species we examined. Their SMR was best described by the equation μW = 1526 * g^0.745 and was not significantly different from that predicted by the standard ‘insect-curve’; but it was significantly higher than that of spiders to which mantises are ecologically more similar than other insects. Mantises consumed meals as large as 138% of their body mass and within 6–12 h of feeding and their metabolic rates doubled before gradually returning to prefeeding rates over the subsequent four days. We found that the SDA responses were isometrically correlated with meal size and the relative cost of digestion was 38% of the energy in each meal. We conclude that mantises provide a promising model to investigate nutritional physiology of insect predators as well as nutrient cycling within their ecological communities.