Participation of breast and leg muscles in shivering thermogenesis in young turkeys and guinea fowl

Do thermal acclimation and an acute heat challenge alter myonuclear domain of control- and fast-growing quail?

Efforts to determine physiological traits that may render species resilient or susceptible to changing global temperatures have accelerated in recent years. Temperature is of critical importance to biological function; thus, climate change has the potential to severely affect all levels of biological organization in many species. For example, increases in environmental temperatures may alter muscle structure and function in birds. Myonuclear domain (MND), an under-studied aspect of avian muscle physiology that changes in response to thermal stress, is defined as the amount of cytoplasm within a muscle fiber that each nucleus is responsible for servicing. Here, we used two random bred lines of Japanese quail (Coturnix japonica) representing examples of control and fast growth rates. We used a factorial design to administer four treatment combinations to each line - an initial period of either heat-stress acclimation (Acclimation) or no acclimation (Not acclimated) followed by either a heat-stress challenge (HS) or no challenge (NC) after week 8 of age - to determine the effects of thermal acclimation and acute thermal stress on quail MND. We found a significant interaction between line * final treatment with fast-growing, HS birds demonstrating the lowest numbers of nuclei per mm of fiber, and Acclimated control-growing birds showing the highest numbers of nuclei per mm of fiber. There was a significant effect of line on MND with the fast-growing line having larger MNDs. Initial treatment with Not Acclimated birds showed larger MNDs. Additionally, control growing quail demonstrated positive correlations with fiber size, whereas fast growing quail did not. This may mean that nuclei in larger fibers of fast-growing quail may be functioning maximally, and that increases in temperature may also demonstrate similar effects.

Thermal acclimation of fast-growing Japanese Quails (Coturnix japonica) exhibit decreased oxidative stress and increased muscle fiber diameters after acute heat challenges

Many predict dire consequences of increasing temperatures; however, high temperatures in early life may aid animals during extreme thermal events later in life. The underlying physiological mechanisms have not been elucidated. We examined whether developing in warmer temperatures would physiologically benefit adult Japanese Quails (Coturnix japonica Temminck and Schlegel, 1849) by exploring changes in oxidative stress and muscle structure in two quail lines — one selected for control growth and another for fast growth and after acute heat challenges. We used a factorial design to administer four treatment combinations to each line: an initial period of either heat-stress acclimation (3 h every other day to 37 °C) or no acclimation, and after 5 weeks, either an acute heat-stress challenge (8 h at 39 °C) or no challenge. We found that control quails had significantly higher citrate synthase activity than fast-growing quails. Fast-growing quails had higher hydroxyl scavenging capacity than control quails. Peroxyl scavenging capacity decreased in both lines after an acute heat challenge, regardless of acclimation. Finally, fast-growing quails had larger muscle fiber diameters than control quails, and acclimated birds that experienced an acute heat challenge had larger muscle fibers than those that did not experience a heat challenge. Thus, fast-growing quails may physiologically benefit from developing in warmer temperatures.

Effects of cold exposure on physiology, meat quality, and behavior of turkey hens and toms crated at transport density

The impact of cold exposure while crated at a density characteristic of transport (83 kg/m2) was assessed in 12-wk-old turkey hens and 16-wk-old toms. Turkeys (72 toms, 72 hens) were randomly divided into 3 male and 3 female groups: 2 moderate 20°C groups with either 30% or 80% RH and a cold group exposed to -18°C, with uncontrolled, high RH. Groups of 8 birds (one replicate unit) were observed in a climate-controlled chamber for 8 h prior to slaughter. Core body temperature (CBT), live shrink, heterophil-lymphocyte ratio (HLR), and change in blood glucose levels were assessed; meat quality measures included thigh and breast muscle pH and L*, a*, and b* color values. Significance was declared at P ≤ 0.05. Live shrink in hens exposed to -18°C (2.8%) was greater (P = 0.001) than those in the 20°C treatments (1.5%). CBT in hens had a tendency to decrease (P = 0.070); no differences in Δ blood glucose or HLR were detected. Thigh pH was higher in the -18°C treatment (hens: 6.39; toms: 6.08) than in both 20°C groups. Color values (L*, a*, and b*) were measured 27 h postmortem. In the -18°C exposed hens, breast L* values were lower, and thigh a* and breast b* values were higher than in both 20°C treatments. No differences were detected in live shrink, CBT, HLR, or color values among toms. Behavior differences were noted between treatments; more time was spent huddling, shivering, preening, and with feathers ptiloerected in cold-exposed turkeys. Generally, cold exposure resulted in higher live shrink, darker meat with greater redness, and a tendency for CBT and blood glucose to decrease, with larger male turkeys experiencing fewer changes.

Increased mass of slow-type skeletal muscles and depressed myostatin gene expression in cold-tolerant chicks

Temperature is maintained in birds by skeletal muscle shivering as well as by non-shivering thermogenesis in a cold environment because they lack brown adipose tissue, which is a mammalian thermogenic organ. Chicks acquire cold tolerance after their skeletal muscles mature. Here, we found that muscle fibers transformed to the slow-twitch type with increasing gene expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), and that the mass increased with decreasing myostatin gene expression, in the leg muscles of 7-day-old and younger chicks within 24 h of cold exposure. Muscle fibers did not transform and the mass did not increase within 24 h of cold exposure in muscles from chicks older than 8 days of age. Myostatin mRNA expression remained depressed in cold-tolerant muscles for 24 h, whereas cold-enhanced growth of the muscle continued for 48 h. Myostatin expression was depressed and muscle mass was increased only in chick leg muscles that comprised both fast- and slow-twitch fibers. These results suggest that the acute regulation of PGC-1alpha and myostatin gene expression in leg muscles is required for chicks to acquire cold tolerance up to 7 days of age.

Developmental dynamics of some blood biochemical parameters in the growing turkey (Meleagris gallopavo)

Blood serum clinical biochemical parameters of fasted BUT Big 8 male turkeys were determined at the ages of 3 days, 4, 8, 12, 16 and 20 weeks, for a follow-up of the developmental changes of some serum metabolites, enzymes and ions. The serum protein content (total protein, albumin, globulin) increased with age, indicating also the moulting-associated metabolic changes in the age interval from the 8th to the 12th weeks. Creatinine was shown to have a peak at 3 days of age (role of muscle activity in thermogenesis), while urate concentration sensitively reflected the dietary protein amount. Serum triglycerides peaked at the time of yolk catabolism, while cholesterol was shown to indicate the moulting, as was serum malondialdehyde. Serum sodium content increased throughout the study. Alanine aminotransferase and aspartate aminotransferase activities increased along the ontogeny, while alkaline phosphatase activity decreased in parallel with the growth. Serum creatine kinase activity showed an over one-magnitude increase. General metabolic and enzymatic alterations were characteristic and applicable for the description of the ontogenetic development of a precocial (post-hatch triglyceride peak), large bodied, meat-type (lactate dehydrogenase, continuously increasing creatine kinase) bird species.

Does food shortage delay development of homeothermy in European shag nestlings (Phalacrocorax aristotelis)?

Nestlings seem to face a trade-off between reducing the basal level of energy metabolism, as an energy-saving response, and maintaining thermogenic capacity during temporal food shortage. In the present study we examined developmental responses to short-term diet restriction of 12-16 day old nestling European shags kept under laboratory conditions and tested whether temporal food shortage delay the development of homeothermy. During food shortage the European shag nestlings substantially reduced basal level of energy metabolism, resulting in significant energy savings. The reduction in basal level of energy metabolism corresponded with a reduction in peak metabolic rate. At the same time, the low peak metabolic rate of diet-restricted nestlings was offset by a lower mass-specific minimal thermal conductance, and an increased mass-specific absolute scope. Consequently, the insulation and the portion of peak metabolic rate available for regulatory thermogenesis seemed to develop normally, as expected from age, during the period of food shortage. Further, the degree of homeothermy, measured as the index of homeothermy, was not significantly lower in diet-restricted nestlings compared to controls at the same age. We conclude that temporal food shortage did not significantly delay the development of homeothermy in the European shag nestlings despite substantial reductions in basal level of energy metabolism and peak metabolic rate.

Energy metabolism and thermoregulation in hand-reared chukars (Alectoris chukar)

Metabolic rate and colonic temperature were measured in chukars between 1st and 108th day of life (divided into six age groups: 1-3-days old, 1, 2, 3, and 4-weeks old and 3.5-months old) in ambient temperatures set separately for each group and ranging from -12 to 41 degrees C. The Gompertz growth constant for growing chukars (0.042) was close to the value obtained in earlier study for the grey partridge. Similarly as in other species of Galliformes, newly hatched chukar chicks had lower T(b) at TNZ (39.5 degrees C) than that found in older birds (41.3 degrees C in 4-weeks old). The body temperatures taken at TNZ in 2-weeks old chicks and older fitted neatly within allometrically predicted limits of body temperatures for adult birds. The values of RMR at TNZ followed closely a biphasic pattern, with the second phase correlating strongly with the body mass. The value of metabolic scope (the level of metabolic efficiency) for the youngest group was high (3.2) and exceeded the values obtained in earlier studies for other gallinaceous species, including the grey partridge. The obtained values of minimum wet thermal conductance for growing chukar chicks exceeded the predicted values by approximately 40% but the slopes of both lines were very similar. In chukars, the key stage in the expression of fully developed thermoregulatory capacities comes immediately after the first week of life (maintaining somewhat constant body temperature, evident drop in the value of RMR at TNZ and minimal thermal conductance). The model of gradual development of thermoregulation which could be derived from the experiments on chukar chicks was characteristic for typical precocial birds.

Growth and Development of Homeothermy in Nestling European Shags (Phalacrocorax Aristotelis)

European Shag (Phalacrocorax aristotelis) nestlings were studied on a small island off the coast of central Norway. Increase in body mass (BM) with age (t, days) was described by the logistic equation: BM = 1,622 g/[1 + e−0.172(t−19.9)]. All growth parameters measured (body mass, and length of tarsus, wing and head) showed highest relative growth rate when the nestlings were 5–10 days old, that is, before the nestlings had achieved homeothermy. An incipient endothermic response was noted when nestlings were 9 days old, and they became homeothermic at ages of 15–18 days. Respective mass-specific resting metabolic rates for nestlings 0, 15, and 45 days old were 47, 261, and 147% of the predicted value for adult nonpasserine birds of similar body masses. Mass-specific minimal thermal conductance decreased from 366% of predicted adult value at hatching, to 220% of that predicted when nestlings were 21 days old. For nestlings 15 days old, the factorial metabolic scope (resting metabolic rate/peak metabolic rate) was only 1.5, but that increased rapidly thereafter. Rapid increase in the mass-specific RMR and decrease in minimal thermal conductance is suggested to contribute importantly to improve homeothermic ability during the first two weeks of the developmental period. At hatching, leg and pectoral muscles constituted 5.3 and 2.2%, respectively, of total wet body mass. Relative leg-muscle mass increased rapidly and had almost reached adult proportions when the nestlings were 25–30 days old. In contrast, pectoral-muscle mass increased in an almost direct proportion to the body mass during the first 30 days of the growth period, and increased rapidly thereafter. At hatching, the water fraction (water content/lipid-free wet mass) was significantly lower in the leg than in the pectoral muscles (0.920 vs. 0.931). The water fraction of leg muscles also remained lower during the entire growth period. Judging from the proportionately greater mass and higher degree of maturity of the leg compared to pectoral muscles, the former would seem to be the main site of cold-induced heat production during early development of homeothermy in European Shag nestlings.

When nonshivering thermogenesis equals maximum metabolic rate: thermal acclimation and phenotypic plasticity of fossorial Spalacopus cyanus (Rodentia)

Many small mammals inhabiting fluctuating and cold environments display enhanced capacity for seasonal changes in nonshivering thermogenesis (NST) and thermoregulatory maximum metabolic rate (MMR). However, it is not known how this plasticity remains in a mammal that rarely experiences extreme thermal fluctuations. In order to answer this question, we determined body mass (m(b)), basal metabolic rate (BMR), NST, MMR, and minimum thermal conductance (C) on a Chilean fossorial caviomorph (Spalacopus cyanus) from a coastal population, acclimated to cold (15 degrees C) and warm (30 degrees C) conditions. NST was measured as the maximum response of metabolic rate (NST(max)) after injection of norepinephrine (NE) in thermoneutrality minus BMR. Maximum metabolic rate was assessed in animals exposed to enhanced heat-loss atmosphere (He-O2) connected with an open-flow respirometer. Body mass and metabolic variables increased significantly after cold acclimation with respect to warm acclimation but to a low extent (BMR, 26%; NST, 10%; and MMR, 12%). However, aerobic scope (MMR/BMR), calculated shivering thermogenesis (ST), and C did not change with acclimation regime. Our data suggest that physiological plasticity of S. cyanus is relatively low, which is in accordance with a fossorial mode of life. Although little is known about MMR and NST in fossorial mammals, S. cyanus has remarkably high NST; low MMR; and surprisingly, a nil capacity of ST when compared with other rodents.

Catabolic capacity of the muscles of shorebird chicks: maturation of function in relation to body size

Newly hatched precocial chicks of arctic shorebirds are able to walk and regulate their body temperatures to a limited extent. Yet, they must also grow rapidly to achieve independence before the end of the short arctic growing season. A rapid growth rate may conflict with development of mature function, and because of the allometric scaling of thermal relationships, this trade-off might be resolved differently in large and small species. We assessed growth (mass) and functional maturity (catabolic enzyme activity) in leg and pectoral muscles of chicks aged 1-16 d and adults of two scolopacid shorebirds, the smaller dunlin (Calidris alpina: neonate mass 8 g, adult mass 50 g) and larger whimbrel (Numenius phaeopus; neonate mass 34 g, adult mass 380 g). Enzyme activity indicates maximum catabolic capacity, which is one aspect of the development of functional maturity of muscle. The growth rate-maturity hypothesis predicts that the development of catabolic capacity should be delayed in faster-growing muscle masses. Leg muscles of both species were a larger proportion of adult size at hatching and grew faster than pectoral muscles. Pectoral muscles grew more rapidly in the dunlin than in the whimbrel, whereas leg muscles grew more rapidly in the whimbrel. In both species and in both leg and pectoral muscles, enzyme activities generally increased with age, suggesting increasing functional maturity. Levels of citrate synthase activity were similar to those reported for other species, but l-3-hydroxyacyl-CoA-dehydrogenase and pyruvate kinase (PK) activities were comparatively high. Catabolic capacities of leg muscles were initially high compared to those of pectoral muscles, but with the exception of glycolytic (PK) capacities, these subsequently increased only modestly or even decreased as chicks grew. The earlier functional maturity of the more rapidly growing leg muscles, as well as the generally higher functional maturity in muscles of the more rapidly growing dunlin chicks, contradicts the growth rate-maturity function trade-off and suggests that birds have considerable latitude to modify this relationship. Whimbrel chicks, apparently, can rely on allometric scaling of power requirements for locomotion and the thermal inertia of their larger mass to reduce demands on their muscles, whereas dunlin chicks require muscles with higher metabolic capacity from an earlier age. Thus, larger and smaller species may adopt different strategies of growth and tissue maturation.

Shivering thermogenesis in leg and breast muscles of galliform chicks and nestlings of the domestic pigeon

We studied the ontogeny of shivering thermogenesis in breast and leg muscles of precocial galliforms (domestic fowl, grey partridge, and Japanese quail) and the altricial domestic pigeon using electromyography (EMG) and indirect calorimetry. Galliforms were able to increase heat production by shivering in leg muscles at the youngest age studied (1-2 d). Pectorals contributed to heat production from days 7-10 onward, but in the partridge and especially in the fowl, shivering by the pectorals was weaker than in the quail. In the pigeon, shivering began in pectorals and legs at 2 and 4 d of age, respectively, and pectorals had clearly the predominant role in thermogenesis. Despite the early beginning of electrical signs of shivering, significant thermogenesis did not appear in the pigeon before the age of 6 d. All galliforms shivered in bursts, like pigeons aged 2-4 d. From the age of 6 d onward, continuous shivering became predominant in the pigeon. In pectorals of 2-6-d-old pigeons, shivering did not increase linearly during decreasing ambient temperature, as in other muscles and species, but started abruptly, at full intensity. Furthermore, in 2-4-d-old pigeons, cooling induced movement activity in legs. The median frequency of shivering EMGs varied (1) with maturation of the muscle, (2) with size of the adult bird, and (3) between altricials and precocials.