Pectoral Mass Research Articles

Measurement of Pectoralis Muscle Quantity and Attenuation by Computed Tomography Using Routinely Available Software is Feasible and Predicts Mortality after LVAD Implantation

Purpose We have previously demonstrated that pectoralis muscle mass and tissue attenuation measured on preoperative CT scans were powerful predictors of mortality after LVAD implantation. These measurements were made with specialized software (Slice-O-Matic) which is not accessible to advanced heart failure teams. The purpose of this analysis was to determine the correlation between pectoralis muscle measures made with specialized software vs. routinely available CT software (PACS). Methods A random sample CT scans (n=57) was selected from our larger LVAD cohort with previously quantified pectoralis muscle measures by Slice-O-Matic Software (larger cohort n=141). Unilateral pectoralis muscle mass indexed to body surface area (PMI) and attenuation (approximated by mean Hounsfield units; PHUm) were re-measured on preoperative chest CT scans by a local radiologist using PACS software. Correlation between Slice-O-Matic and PACS pectoralis muscle measures was performed with Pearson analysis. These measures (PACS) were then assessed as predictors of mortality after LVAD implantation using multivariate cox regression. Results We observed a high correlation between pectoralis muscle measures using both techniques (R = 0.95 for PMI, R = 0.94 for PHUm). For the pectoralis measures quantified by PACS, each unit increase in PMI was associated with a 31% reduction in the hazard of death after LVAD (adjusted HR 0.69, 95% CI 0.48-0.99, p = 0.046). Each 5-unit increase in PHUm was associated with a 39% reduction in the hazard of death after LVAD (adjusted HR 0.61, 95% CI 0.38-0.96, p Conclusion Pectoralis muscle measurements can be performed by local radiologists using routinely available software. These measures are predictive of morality following LVAD. This is an important first step in delivering a predictive model incorporating this measure into real world practice.

A Novel Model Incorporating Pectoralis Muscle Measures to Predict Mortality after Ventricular Assist Device Implantation

Purpose We have previously shown that pectoralis muscle mass and tissue attenuation obtained on preoperative CT scans were powerful predictors of mortality after LVAD implantation using single center data. This analysis confirms those findings in a separate LVAD dataset and presents a novel prediction model developed across centers. Methods Patients with chest CTs performed ≤ 3 months before LVAD implantation at University of Minnesota (n=143) and Houston Methodist Hospital (n=133) were identified from larger cohorts (University of Minnesota n=353, Houston Methodist =278). Unilateral pectoralis muscle mass indexed to body surface area (PMI) and attenuation (approximated by mean Hounsfield units; PHUm) were measured on preoperative chest CT scans. To develop the Pectoralis Muscle Risk Score (PMRS), we implemented a cross-validated model selection using Cox's proportional hazards regression model with censoring at transplantation. The final model included PHUm, sex, albumin, year of implant, body mass index, bridge to transplant, INTERMACS profile, and presence or absence of contrast. Receiver-operating characteristic (ROC) curves for 30, 90, and 365 day survival were generated for the model and compared to the HeartMate II Risk Score (HMRS). Results The Pectoralis Risk Score outperformed HMRS at each of the pre-specified time-points. The AUC for PMRS for predicting survival at 30, 90, and 365 days was 78%, 76%, and 76%, respectively. The HMRS had AUC of 63%, 67%, and 63% (Figure). Conclusion The Pectoralis Muscle Risk Score had favorable discrimination in this multicenter dataset. These skeletal muscle measures, which are associated with heart failure stage and frailty, appear to add important information to pre-operative risk assessment.

What determines the basal rate of metabolism?

The basal rate of metabolism (BMR) is the most reported estimate of energy expenditure in endotherms. Its principal determinant is body mass, but BMR also correlates with a variety of behavioral and ecological factors that do not determine basal rate: they are byproducts of the mechanisms that are its determinate. In mammals, mass-independent BMR increases when muscle mass is >40% of total body mass and BMR is then ≥100% of the value expected from body mass. Mammals with muscle masses <30% of body mass have lower BMRs, a diminished capacity to regulate body temperature and often have reduced activity levels. At muscle masses <42% of body mass, birds have body temperatures and basal rates higher than mammals with the same muscle mass. Their high basal rates derive from fast blood flow and increased mitochondrial density in their pectoral muscles. These enhancements also occur in the flight muscles of bats. Oxygen transport to the pectoral muscles of birds is facilitated by an increase in heart mass and hematocrit. This arrangement avoids transporting a large muscle mass to fuel flight, thereby reducing the cost of flight. Pectoral muscle masses <9% of body mass correlate with a flightless condition in kiwis, rails and ducks but some fruit pigeons have BMRs as low as those measured in kiwis, while remaining volant. The mass-independent BMRs of endotherms principally reflect changes of muscle activity and mass. An increase in muscle mass may have contributed to the evolution of endothermy.

Empyema necessitatis due to Citrobacter freundii: Case report

Introduction: This paper presents the first case of empyema necessitatis secondary to infection with Citrobacter freundii (according to the databases consulted), and one of the few reports of this pathology in Colombia.Case presentation: This is the case of a 26-year-old patient from a rural area, with a history of severe cognitive deficit, who was taken to the emergency department due to a clinical picture of 15 days of evolution consisting of neurological deterioration associated with asthenia, adynamia, fever and cough with purulent expectoration. On admission, a chest x-ray was taken, finding pneumonia of the middle lobe with associated pleural effusion, for which empirical antibiotic management was initiated. The patient presented clinical deterioration and appearance of right pectoral mass, so a computed tomography of the thorax was performed, revealing empyema necessitatis. Close drainage and culture of the collection were made, with negative mycobacteria culture and positive report for C. freundii. The patient received specific antibiotic treatment for 8 weeks, with complete improvement of his clinical condition.Conclusion: Besides being the first case of empyema necessitatis by C. freundii that has been reported, this case is important because of the low amount of reports on this pathology in Colombia, considering that its main cause is tuberculosis, which is endemic in the country.

Large muscles are beneficial but not required for improving thermogenic capacity in small birds

It is generally assumed that small birds improve their shivering heat production capacity by developing the size of their pectoralis muscles. However, some studies have reported an enhancement of thermogenic capacity in the absence of muscle mass variation between seasons or thermal treatments. We tested the hypothesis that an increase in muscle mass is not a prerequisite for improving avian thermogenic capacity. We measured basal (BMR) and summit (Msum) metabolic rates of black capped chickadees (Poecile atricapillus) acclimated to thermoneutral (27 °C) and cold (−10 °C) temperatures and obtained body composition data from dissections. Cold acclimated birds consumed 44% more food, and had 5% and 20% higher BMR and Msum, respectively, compared to individuals kept at thermoneutrality. However, lean dry pectoralis and total muscle mass did not differ between treatments, confirming that the improvement of thermogenic capacity did not require an increase in skeletal muscle mass. Nevertheless, within temperature treatments, Msum was positively correlated with the mass of all measured muscles, including the pectoralis. Therefore, for a given acclimation temperature individuals with large muscles do benefit from muscle size in term of heat production but improving thermogenic capacity during cold acclimation likely requires an upregulation of cell functions.

Sex-Specific Effects of Incubation Temperature on Embryonic Development of Zebra Finch (Taeniopygia guttata) Embryos.

In oviparous species, the embryonic environment-particularly temperature-can alter phenotype and survival of an individual by affecting its size as well as its metabolic rate. Previous studies have shown that incubation temperatures can affect sex ratio in birds; specifically, low incubation temperatures were shown to produce a male-biased sex ratio in zebra finches (Taeniopygia guttata) possibly because of a higher pre- or postnatal mortality rate in females. We hypothesized that sexes respond differently to suboptimal incubation temperature, leading to a male-biased sex ratio. To test this hypothesis, zebra finch eggs were incubated at 36.1°, 37.5°, or 38.5°C and hatching success, hatchling mass, residual yolk mass, and pectoralis mass were measured. We found that while hatchling mass was similar between the sexes at 37.5°C, female hatchlings were heavier at 36.1°C, and male hatchlings were heavier at 38.5°C. Pectoralis muscle mass was similar between the sexes at 36.1°C; however, at 37.5°C, female pectoralis mass was heavier at hatching than that of males. Females at 37.5°C also had lower residual yolk at hatching compared with males, reflecting a higher use of energy by female embryos compared with male embryos at this temperature. In contrast, residual yolk was similar between the sexes at 36.1° and 38.5°C. Our results suggest that there are sex differences in how incubation temperature alters organ mass and yolk energy reserve; this can lead to a difference in survival at different incubation temperatures between the sexes. Taken together with previous studies showing that females alter incubation behavior with ambient temperature, rising ambient temperatures could impact phenotype and survival of avian offspring in a sex-specific manner.

Investigating Meat Quality of Broiler Chickens Fed on Heat Processed Diets Containing Corn Distillers Dried Grains with Solubles.

The present study investigated the effects of feed form and distiller’s dried grain with solubles (DDGS) on meat quality and fatty acids profile of broiler chickens. A total of 720 broilers (Ross 308; average BW [body weight] 541±5.7 g) were randomly allotted to six treatments. Birds were fed three different feed forms (mash; SP, simple pellet; EP, expanded pellet) and DDGS (0 or 200 g kg–1) in a 3×2 factorial arrangement. The addition of DDGS and EP to the diet resulted in increased shear force of breast meat. Moreover, DDGS inclusion in the diet reduced the concentration of stearic acid and behenic acid in thigh meat. Pelleting (SP and EP) of the diets increased palmitic acid content in the thigh, whereas the linolenic acid content decreased. The breast mass was higher with EP and SP diets than with the mash diet. Feed processing led to increased pectoralis muscle and drum mass compared to mash-fed chickens. In conclusion, our results demonstrated that EP decreased thigh linolenic acid and meat shear force. In addition, DDGS supplementation in broiler hampers meat quality by increasing the shear force.

A Risk Model Incorporating Pectoralis Muscle Measures More Accurately Risk Predicts Mortality after Left Ventricular Assist Device Implantation

Pectoralis muscle mass and tissue attenuation obtained on preoperative CT scans are powerful predictors of mortality after LVAD implantation. A multivariable prediction model incorporating pectoralis muscle measures was created and tested in this analysis.

Experimental Increases in Foraging Costs Affect Pectoralis Muscle Mass and Myostatin Expression in Female, but Not Male, Zebra Finches (Taeniopygia guttata).

Skeletal muscle remodeling is an important component of phenotypic flexibility in birds and impacts organismal metabolism and performance, which could potentially influence fitness. One regulator of skeletal muscle remodeling is myostatin, an autocrine/paracrine muscle growth inhibitor that may be down-regulated under conditions promoting heavier muscle masses. In this study, we employed protocols requiring hovering while foraging to increase foraging costs and modify phenotypes of zebra finches (Taeniopygia guttata). We examined the effects of high-cost foraging (HF) on skeletal muscle masses and used real-time reverse-transcription polymerase chain reaction and Western blots to measure gene and protein expression of myostatin and its metalloproteinase activators tolloid-like proteases TLL-1 and TLL-2 in pectoralis muscle. Female finches average shorter wings and higher wing loading than males, so increased flight costs might be expected to disproportionately affect females. Indeed, HF female finches exhibited reduced total fat masses, increased pectoralis muscle masses, and lower myostatin protein levels than controls. Male finches showed no significant differences in pectoralis muscle masses or myostatin protein levels between HF and control birds. Myostatin, TLL-1, and TLL-2 messenger RNA (mRNA) expression remained stable between treatments for both female and male finches. Myostatin mRNA and protein levels showed variable directions of correlations with pectoralis mass residuals among treatments. Thus, these data offer only mixed support for a regulatory role for myostatin in mediating the flexibility of pectoralis muscle phenotypes of small birds.

Comparative Transcriptomics of Seasonal Phenotypic Flexibility in Two North American Songbirds.

Phenotypic flexibility allows organisms to reversibly alter their phenotypes to match the changing demands of seasonal environments. Because phenotypic flexibility is mediated, at least in part, by changes in gene regulation, comparative transcriptomic studies can provide insights into the mechanistic underpinnings of seasonal phenotypic flexibility, and the extent to which regulatory responses to changing seasons are conserved across species. To begin to address these questions, we sampled individuals of two resident North American songbird species, American goldfinch (Spinus tristis) and black-capped chickadee (Poecile atricapillus) in summer and winter to measure seasonal variation in pectoralis transcriptomic profiles and to identify conserved and species-specific elements of these seasonal profiles. We found that very few genes exhibited divergent responses to changes in season between species, and instead, a core set of over 1200 genes responded to season concordantly in both species. Moreover, several key metabolic pathways, regulatory networks, and gene functional classes were commonly recruited to induce seasonal phenotypic shifts in these species. The seasonal transcriptomic responses mirror winter increases in pectoralis mass and cellular metabolic intensity documented in previous studies of both species, suggesting that these seasonal phenotypic responses are due in part to changes in gene expression. Despite growing evidence of muscle nonshivering thermogenesis (NST) in young precocial birds, we did not find strong evidence of upregulation of genes putatively involved in NST during winter in either species, suggesting that seasonal modification of muscular NST is not a prominent contributor to winter increases in thermogenic capacity for adult passerine birds. Together, these results provide the first comprehensive overview of potential common regulatory mechanisms underlying seasonally flexible phenotypes in wild, free-ranging birds.

Preoperative Pectoralis Muscle Quantity and Attenuation by Computed Tomography Are Novel and Powerful Predictors of Mortality After Left Ventricular Assist Device Implantation.

Skeletal muscle mass decreases in end-stage heart failure and is predictive of clinical outcomes in several disease states. Skeletal muscle attenuation and quantity as quantified on preoperative chest computed tomographic scans may be predictive of mortality after continuous flow (CF) left ventricular assist device (LVAD) implantation. A single-center continuous flow-LVAD database (n=354) was used to identify patients with chest computed tomographies performed in the 3 months before LVAD implantation (n=143). Among patients with computed tomography data available, unilateral pectoralis muscle mass indexed to body surface area and attenuation (approximated by mean Hounsfield units [PHUm]) were measured in each patient with a high intrarater and inter-rater reliability (intraclass correlation coefficients 0.98 and 0.97, respectively). Multivariate Cox regression analyses were performed, censoring at cardiac transplantation, to assess the impact of preoperative pectoralis muscle index and pectoralis muscle mean Hounsfield unit on survival after LVAD implantation. Each unit increase in pectoralis muscle index was associated with a 27% reduction in the hazard of death after LVAD (adjusted hazard ratio, 0.73; 95% confidence interval, 0.58-0.92; P=0.007). Each 5-U increase in pectoralis muscle mean Hounsfield unit was associated with a 22% reduction in the hazard of death after LVAD (adjusted hazard ratio, 0.78; 95% confidence interval, 0.68-0.89; P<0.0001). Pectoralis muscle index and pectoralis muscle mean Hounsfield unit outperformed other traditional measures in the data set, including the HeartMate II risk score. Pectoralis muscle size and attenuation were powerful predictors of outcomes after LVAD implantation in this data set. This one time, repeatable, internal assessment of patient substrate added valuable prognostic information that was not available on standard preoperative testing.

Mitochondrial oxidative phosphorylation efficiency is upregulated during fasting in two major oxidative tissues of ducklings

Fasted endothermic vertebrates must develop physiological responses to maximize energy conservation and survival. The aim of this study was to determine the effect of 1-wk. fasting in 5-wk. old ducklings (Cairina moschata) from whole-body resting metabolic rate and body temperature to metabolic phenotype of tissues and mitochondrial coupling efficiency. At the level of whole organism, the mass-specific metabolic rate of ducklings was decreased by 40% after 1-wk. of fasting, which was associated with nocturnal Tb declines and shallow diurnal hypothermia during fasting. At the cellular level, fasting induced a large reduction in liver, gastrocnemius (oxidative) and pectoralis (glycolytic) muscle masses together with a fuel selection towards lipid oxidation and ketone body production in liver and a lower glycolytic phenotype in skeletal muscles. At the level of mitochondria, fasting induced a reduction of oxidative phosphorylation activities and an up-regulation of coupling efficiency (+30% on average) in liver and skeletal muscles. The present integrative study shows that energy conservation in fasted ducklings is mainly achieved by an overall reduction in mitochondrial activity and an increase in mitochondrial coupling efficiency, which would, in association with shallow hypothermia, increase the conservation of endogenous fuel stores during fasting.

Context-dependent regulation of pectoralis myostatin and lipid transporters by temperature and photoperiod in dark-eyed juncos

A prominent example of seasonal phenotypic flexibility is the winter increase in thermogenic capacity (=summit metabolism, ) in small birds, which is often accompanied by increases in pectoralis muscle mass and lipid catabolic capacity. Temperature or photoperiod may be drivers of the winter phenotype, but their relative impacts on muscle remodeling or lipid transport pathways are little known. We examined photoperiod and temperature effects on pectoralis muscle expression of myostatin, a muscle growth inhibitor, and its tolloid-like protein activators (TLL-1 and TLL-2), and sarcolemmal and intracellular lipid transporters in dark-eyed juncos Junco hyemalis. We acclimated winter juncos to four temperature (3 °C or 24 °C) and photoperiod [short-day (SD) = 8L:16D; long-day (LD) = 16L:8D] treatments. We found that myostatin, TLL-1, TLL-2, and lipid transporter mRNA expression and myostatin protein expression did not differ among treatments, but treatments interacted to influence lipid transporter protein expression. Fatty acid translocase (FAT/CD36) levels were higher for cold SD than for other treatments. Membrane-bound fatty acid binding protein (FABPpm) levels, however, were higher for the cold LD treatment than for cold SD and warm LD treatments. Cytosolic fatty acid binding protein (FABPc) levels were higher on LD than on SD at 3 °C, but higher on SD than on LD at 24 °C. Cold temperature groups showed upregulation of these lipid transporters, which could contribute to elevated Msum compared to warm groups on the same photoperiod. However, interactions of temperature or photoperiod effects on muscle remodeling and lipid transport pathways suggest that these effects are context-dependent.

Is cestode infection intensity associated with decreased body condition in the Eurasian woodcock Scolopax rusticola?

The Eurasian woodcock Scolopax rusticola is a widespread woodland specialist and a widely harvested quarry species throughout its European wintering areas, including Britain. Woodcock are prone to cestodiasis, but prevalence levels and possible effects on body condition remain under-studied. We studied the prevalence, abundance and intensity of cestodiasis in 161 woodcock harvested in four British regions in December and January during two consecutive winters (2013/14 and 2014/15). Cestodiasis prevalence was 90%, and there was no difference in prevalence between birds harvested in Cornwall, Wessex, East Anglia and Scotland. High prevalence levels were explained by the fact that earthworms (Lumbricidae) are intermediate hosts for some cestode species and also the most important dietary component of woodcock. The distribution of cestodiasis in woodcock was aggregated, such that when using the total length of cestodes per sample to measure abundance, 65% of the birds had less than 80 cm. Cestodiasis abundance varied between sexes across regions but the intensity was not affected by region, sex, age or their interactions. The intensity of cestodiasis was positively correlated with fresh weight and pectoral mass, while no significant correlation was found with the abdominal fat pad. Our results suggest that, despite high prevalence levels and intensity of cestodiasis in woodcock, host body condition is not significantly affected and hence it is unlikely that cestodiasis has a major effect on woodcock population dynamics.

Within-Winter Flexibility in Muscle Masses, Myostatin, and Cellular Aerobic Metabolic Intensity in Passerine Birds.

Metabolic rates of passerine birds are flexible traits that vary both seasonally and among and within winters. Seasonal variation in summit metabolic rates (Msum = maximum thermoregulatory metabolism) in birds is consistently correlated with changes in pectoralis muscle and heart masses and sometimes with variation in cellular aerobic metabolic intensity, so these traits might also be associated with shorter-term, within-winter variation in metabolic rates. To determine whether these mechanisms are associated with within-winter variation in Msum, we examined the effects of short-term (ST; 0-7 d), medium-term (MT; 14-30 d), and long-term (LT; 30-yr means) temperature variables on pectoralis muscle and heart masses, pectoralis expression of the muscle-growth inhibitor myostatin and its metalloproteinase activators TLL-1 and TLL-2, and pectoralis and heart citrate synthase (CS; an indicator of cellular aerobic metabolic intensity) activities for two temperate-zone resident passerines, house sparrows (Passer domesticus) and dark-eyed juncos (Junco hyemalis). For both species, pectoralis mass residuals were positively correlated with ST temperature variables, suggesting that cold temperatures resulted in increased turnover of pectoralis muscle, but heart mass showed little within-winter variation for either species. Pectoralis mRNA and protein expression of myostatin and the TLLs were only weakly correlated with ST and MT temperature variables, which is largely consistent with trends in muscle masses for both species. Pectoralis and heart CS activities showed weak and variable trends with ST temperature variables in both species, suggesting only minor effects of temperature variation on cellular aerobic metabolic intensity. Thus, neither muscle or heart masses, regulation by the myostatin system, nor cellular aerobic metabolic intensity varied consistently with winter temperature, suggesting that other factors regulate within-winter metabolic variation in these birds.

Phenotypic flexibility of skeletal muscle and heart masses and expression of myostatin and tolloid-like proteinases in migrating passerine birds.

Migrant birds require large flight muscles and hearts to enhance aerobic capacity and support sustained flight. A potential mechanism for increasing muscle and heart masses during migration in birds is the muscle growth inhibitor myostatin and its metalloproteinase activators, tolloid-like proteinases (TLL-1 and TLL-2). We hypothesized that myostatin, TLL-1 and TLL-2 are downregulated during migration in pectoralis and hearts of migratory passerines to promote hypertrophy. We measured seasonal variation of tissue masses, mRNA expression of myostatin, TLL-1, and TLL-2, and myostatin protein levels in pectoralis muscle and heart for yellow warblers (Setophaga petechia), warbling vireos (Vireo gilvus), and yellow-rumped warblers (Setophaga coronata). Pectoralis mass was greatest in spring for warbling vireos and yellow warblers, but was stable between spring and fall for yellow-rumped warblers. Heart mass was higher in spring than in fall for yellow-rumped warblers, lowest in fall for warbling vireos, and seasonally stable for yellow warblers. Pectoralis and heart mRNA expression of myostatin and the TLLs did not differ significantly for any of the three species, offering little support for our hypothesis for a prominent role for myostatin in regulating migration-induced variation in pectoralis and heart masses. In contrast, pectoralis myostatin protein levels were lowest in spring for all three species, consistent with our hypothesis. Myostatin protein levels in heart, however, were seasonally stable for warbling vireos and yellow warblers, and increased in spring relative to fall for yellow-rumped warblers. These data offer mixed support for our hypothesis for the pectoralis, but suggest that myostatin is not a prominent regulator of migration-induced heart hypertrophy. Moreover, the different seasonal patterns for pectoralis mRNA and protein expression suggest that post-transcriptional modification of myostatin may contribute to pectoralis mass regulation during migration.

Acute cold and exercise training up-regulate similar aspects of fatty acid transport and catabolism in house sparrows (Passer domesticus).

Summit maximum thermoregulatory metabolic rate (Msum) and maximum exercise metabolic rate (MMR) both increase in response to acute cold or exercise training in birds. Because lipids are the main fuel supporting both thermogenesis and exercise in birds, adjustments to lipid transport and catabolic capacities may support elevated energy demands from cold and exercise training. To examine a potential mechanistic role for lipid transport and catabolism in organismal cross-training effects (exercise effects on both exercise and thermogenesis, and vice versa), we measured enzyme activities and mRNA and protein expression in pectoralis muscle for several key steps of lipid transport and catabolism pathways in house sparrows (Passer domesticus) during acute exercise and cold training. Both training protocols elevated pectoralis protein levels of fatty acid translocase (FAT/CD36), cytosolic fatty acid-binding protein, and citrate synthase (CS) activity. However, mRNA expression of FAT/CD36 and both mRNA and protein expression of plasma membrane fatty acid-binding protein did not change for either training group. CS activities in supracoracoideus, leg and heart, and carnitine palmitoyl transferase (CPT) and β-hydroxyacyl CoA-dehydrogenase activities in all muscles did not vary significantly with either training protocol. Both Msum and MMR were significantly positively correlated with CPT and CS activities. These data suggest that up-regulation of trans-sarcolemmal and intramyocyte lipid transport capacities and cellular metabolic intensities, along with previously documented increases in body and pectoralis muscle masses and pectoralis myostatin (a muscle growth inhibitor) levels, are common mechanisms underlying the training effects of both exercise and shivering in birds.

Cross-training in birds: cold and exercise training produce similar changes in maximal metabolic output, muscle masses and myostatin expression in house sparrows (Passer domesticus).

Maximal metabolic outputs for exercise and thermogenesis in birds presumably influence fitness through effects on flight and shivering performance. Because both summit (Msum, maximum thermoregulatory metabolic rate) and maximum (MMR, maximum exercise metabolic rate) metabolic rates are functions of skeletal muscle activity, correlations between these measurements and their mechanistic underpinnings might occur. To examine whether such correlations occur, we measured the effects of experimental cold and exercise training protocols for 3 weeks on body (Mb) and muscle (Mpec) masses, basal metabolic rate (BMR), Msum, MMR, pectoralis mRNA and protein expression for myostatin, and mRNA expression of TLL-1 and TLL-2 (metalloproteinase activators of myostatin) in house sparrows (Passer domesticus). Both training protocols increased Msum, MMR, Mb and Mpec, but BMR increased with cold training and decreased with exercise training. No significant differences occurred for pectoralis myostatin mRNA expression, but cold and exercise increased the expression of TLL-1 and TLL-2. Pectoralis myostatin protein levels were generally reduced for both training groups. These data clearly demonstrate cross-training effects of cold and exercise in birds, and are consistent with a role for myostatin in increasing pectoralis muscle mass and driving organismal increases in metabolic capacities.

Poultry Carcasses Chilled by Forced Air, Water Immersion and Combination of Forced Air and Water Immersion

Conventional chilling methods such as forced air (FA) and water immersion (WI) are used in the industry to chill poultry carcasses from approximately 40 to 4C, which is essential to improve safety. Besides both processes, a combined method (CO) of WI and FA has been reported in the literature. The objective of this investigation was to compare the chilling of poultry carcasses by FA, WI and CO using an experimental apparatus specially designed for this purpose. Time-temperature evolutions of pectoral muscle and carcass mass variations during the chilling processes were determined under different chilling conditions, comprising different air velocities and relative humidities (RH). The results showed that it is possible to reduce the water loss (approximately 50%) and chilling time (reduction between 14.5 and 1.5%) of FA process using CO process. Air velocity and RH ranges can be varied to take advantage of evaporative chilling and to reduce the carcasses water loss. Practical Applications In the factories, poultry carcasses are chilled from approximately 40 to 4C by water immersion, which is crucial to ensure safe products. However, air chilling (AC) has been often used for safety reason and due to the limited availability of water. On the contrary, wetting the carcasses avoids excessive moisture loss in air chillers, whereas the evaporation of the water adhered to the carcass surface may assist the chilling process. The present paper evaluates the effectiveness of AC and of a combined chilling method (CC) (AC combined with water immersion chilling) of poultry carcasses at different relative humidity and air velocities. The results showed that the CC process was shorter and reduced carcasses weight loss compared with the AC process.

Mechanistic drivers of flexibility in summit metabolic rates of small birds.

Flexible metabolic phenotypes allow animals to adjust physiology to better fit ecological or environmental demands, thereby influencing fitness. Summit metabolic rate (Msum = maximal thermogenic capacity) is one such flexible trait. Skeletal muscle and heart masses and myocyte metabolic intensity are potential drivers of Msum flexibility in birds. We examined correlations of skeletal muscle and heart masses and pectoralis muscle citrate synthase (CS) activity (an indicator of cellular metabolic intensity) with Msum in house sparrows (Passer domesticus) and dark-eyed juncos (Junco hyemalis) to determine whether these traits are associated with Msum variation. Pectoralis mass was positively correlated with Msum for both species, but no significant correlation remained for either species after accounting for body mass (Mb) variation. Combined flight and leg muscle masses were also not significantly correlated with Msum for either species. In contrast, heart mass was significantly positively correlated with Msum for juncos and nearly so (P = 0.054) for sparrows. Mass-specific and total pectoralis CS activities were significantly positively correlated with Msum for sparrows, but not for juncos. Thus, myocyte metabolic intensity influences Msum variation in house sparrows, although the stronger correlation of total (r = 0.495) than mass-specific (r = 0.378) CS activity with Msum suggests that both pectoralis mass and metabolic intensity impact Msum. In contrast, neither skeletal muscle masses nor pectoralis metabolic intensity varied with Msum in juncos. However, heart mass was associated with Msum variation in both species. These data suggest that drivers of metabolic flexibility are not uniform among bird species.