Magnitude Of Specific Dynamic Action Research Articles

Effect of dietary protein on energy metabolism including protein synthesis in the spiny lobster Sagmariasus verreauxi

This is the first study in an aquatic ectotherm to combine a stoichiometric bioenergetic approach with an endpoint stochastic model to explore dietary macronutrient content. The combination of measuring respiratory gas (O2 and CO2) exchange, nitrogenous (ammonia and urea) excretion, specific dynamic action (SDA), metabolic energy substrate use, and whole-body protein synthesis in spiny lobster, Sagmariasus verreauxi, was examined in relation to dietary protein. Three isoenergetic feeds were formulated with varying crude protein: 40%, 50% and 60%, corresponding to CP40, CP50 and CP60 treatments, respectively. Total CO2 and ammonia excretion, SDA magnitude and coefficient, and protein synthesis in the CP60 treatment were higher compared to the CP40 treatment. These differences demonstrate dietary protein influences post-prandial energy metabolism. Metabolic use of each major energy substrate varied at different post-prandial times, indicating suitable amounts of high-quality protein with major non-protein energy-yielding nutrients, lipid and carbohydrate, are critical for lobsters. The average contribution of protein oxidation was lowest in the CP50 treatment, suggesting mechanisms underlying the most efficient retention of dietary protein and suitable dietary inclusion. This study advances understanding of how deficient and surplus dietary protein affects energy metabolism and provides approaches for fine-scale feed evaluation to support sustainable aquaculture.

The use of stoichiometric bioenergetics to elucidate metabolic energy substrate use and specific dynamic action in cultured juvenile spiny lobsters (Sagmariasus verreauxi) of different nutritional status

Simultaneous measurements of nitrogenous (ammonia and urea) excretion and respiratory gas (O2 and CO2) exchange provide a non-destructive stoichiometric bioenergetic approach to elucidate metabolic energy substrate use which has rarely been used with aquatic ectotherms due to previous difficulties in measuring total CO2 excretion. This study examined metabolic energy substrate use and specific dynamic action (SDA) in cultured spiny lobster, Sagmariasus verreauxi, of different nutritional status. SDA magnitude calculated by stoichiometry was compared to a traditional composite oxycalorific coefficient approach. Protein synthesis can account for a large part of SDA in aquatic ectotherms. This study used a protein synthesis inhibitor cycloheximide to investigate the contribution of cycloheximide-sensitive protein synthesis to SDA and the effect of cycloheximide on nitrogenous and CO2 excretion. Lobsters were subjected to five treatments: 2-day fasted juveniles sham injected with saline (FS treatment); 2-day fasted juveniles injected with cycloheximide (FC treatment); 10-day starved juveniles injected with cycloheximide (SC treatment); post-prandial juveniles fed squid Nototodarus sloanii (FED treatment) and; post-prandial juveniles injected with cycloheximide (FEDC treatment). Protein was the primary energy substrate (65% of oxygen consumption) for 2-day fasted juveniles, with lipid accounting for the remainder (35%). After 10-day starvation lipid became the main substrate, indicating lipid oxidation increased with extended fasting. Following feeding, protein contribution remained above 50%, while lipid (0–43%) and carbohydrate (0–37%) provided significant energy at different time periods, indicating besides protein appropriate proportions of non-protein ingredients are also essential to lobsters. SDA magnitude in FED and FEDC treatments estimated by the traditional approach was 10.5 and 0.4 J g−1, respectively, indicating S. verreauxi expended 96% of post-prandial energy on protein synthesis and that decapod protein synthesis can account for one of the highest proportions of SDA in aquatic ectotherms. SDA magnitude in the FED treatment evaluated by stoichiometry (12.6 J g−1) was comparable to the traditional approach. Interestingly, stoichiometry was not applicable in the FEDC treatment as the respiratory quotient exceeded the theoretical maximum under aerobic conditions. Cycloheximide did not affect CO2 excretion among all treatments or nitrogenous excretion among unfed treatments, while the post-treatment total nitrogenous excretion reduced in fed lobsters. The combined measurement of substrate use and SDA potentially helps optimize the feed to achieve sustainable aquaculture. However, more research is required to decipher limitations and the applicability of stoichiometry for crustaceans.

Going to sleep with a full belly: Thermal substitution by specific dynamic action in shorebirds

Many bird species occupy habitats where environmental temperatures fall well below their thermoneutral zone (TNZ), so they must deal with high energy costs of thermoregulation to keep in heat balance. In such circumstances, specific dynamic action (SDA) - also referred to as heat increment of feeding - could be used to substitute for these high thermoregulatory costs. If birds ingest food before going to roost in cold environments, the SDA will be beneficial as an energy-conserving mechanism by thermal substitution. We investigated the magnitude and duration of SDA in a small-sized shorebird, the dunlin Calidris alpina, while feeding on living prey. We simulated in the aviary the food availability of a semidiurnal tidal cycle, and calculated the thermal substitution by SDA below their TNZ at the beginning of the “high tide” (resting period), after feeding ad libitum during the “low tide” (feeding period). Within TNZ (25 °C), dunlins consumed 12% (2.15 kJ) of the gross energy intake in excess by the SDA, with a duration of ~95 min. At 10 °C, i.e. below the lower critical limit of TNZ, SDA magnitude and duration were reduced by 29% and 31%, respectively. The amount of food ingested significantly affected the duration and magnitude of SDA, as well as the dunlin’s body temperature. Thermal substitution by SDA saved 11% of the dunlin’s theoretical daily energy requirement during winter. This thermal substitution could be commonly used by birds going to roost in cold climates. Interacting with other different behavioral and/or physiological strategies would help to maintain lower energetic costs and enhance survival in cold environments.

Nutritional physiology of mahi-mahi (Coryphaena hippurus): Postprandial metabolic response to different diets and metabolic impacts on swim performance

Migratory pelagic fish species, such as the mahi-mahi (Coryphaena hippurus), must balance numerous metabolic demands simultaneously in order to survive in a challenging oceanic environment. Energetic support for such demands comes from a variety of natural prey items in the wild and can come from manufactured pelletized feed in captivity. This study quantified postprandial metabolism, commonly referred to as specific dynamic action (SDA), over time in adult mahi-mahi (706±25g; 38±0.7cm FL) in response to satiation feeding using three different natural and manufactured diets. Results indicate that during satiation feeding the amount of food ingested is dictated by energy content rather than prey mass, regardless of moisture content of the diet. Ingested meal energy did not differ significantly across groups (473±45kJ), nor did the duration of SDA (36±2.1h). Satiation feeding levels ranged from 2.9–16.2% bodyweight depending on the diet. Peak SDA and SDA magnitude were both significantly decreased in response to dry pelletized diet compared to the natural forage diets, despite equivalent energy consumption. Swim performance and maximum metabolic rate were not impacted significantly in satiation fed fish compared to unfed fish, supporting the evidence that mahi-mahi are able to maintain multiple metabolic demands at one time without compromising performance.

Effect of food on specific dynamic action (SDA) of green and red types of sea cucumber (Apostichopus japonicus Selenka)

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and absorption, is strongly affected by food type. Effects of formulated diet (FMD), macroalgae (ALG) and sea mud (SMD) diets on the postprandial metabolic response of the green type and the red type of sea cucumber (Apostichopus japonicus) were studied in order to understand their feeding physiology. Food offered to A. japonicus was different in protein, lipid content and energy but not in meal mass. SDA of A. japonicus resulted in a 1.3–2.7 folds of increase in oxygen consumption that can persist for up to 4.8–31.7 h after digesting three different diets. In a given type of sea cucumber, the magnitude of SDA was the highest when fed with FMD, medium with ALG, and the lowest with SMD, which is probably due to the differences in diet components and protein contents. The red type sea cucumber showed greater SDA magnitude than the green type with each diet treatment, which might result from the difference in factorial scope between the two types of sea cucumber. However, the smallest magnitude or even no difference was observed between the two types of A. japonicus in SMD group, perhaps owing to the poor nutrition and digestion of sea mud.

The effect of protein and lipid level on the specific dynamic action and post-prandial nitrogen excretion in subadult of white shrimp Litopenaeus vannamei

The study aimed to evaluate the effect of 4 levels of dietary protein (20, 30, 40 and 50%) and lipids (2, 4, 8 and 16%) on the magnitude and duration of specific dynamic action (SDA) and postprandial nitrogen excretion in the subadult white shrimp Litopenaeus vannamei using computer-controlled metabolic chambers (continuous-flow respirometer). We determined the oxygen consumption rate at 1 h intervals until the postprandial oxygen consumption rate returned to the pre-feeding level. Shrimp fed all the diets had significantly higher respiration rates after feeding due to the SDA. Oxygen consumption, the SDA coefficient and the SDA magnitude increased notably with increasing dietary protein content. Shrimp fed the 20% protein diet had the lowest levels of pre- and post-feeding respiration and the smallest SDA. A significant change in the SDA coefficient relative to each lipid level was not demonstrable. Additionally, nitrogenous excretion increased with an increase of dietary protein but not with an increase of lipid level. By estimating the SDA of subadults, the response to standard metabolic rate (SMR) was lower than that reported for juveniles and postlarva white shrimp

The effect of temperature and ration size on specific dynamic action and production performance in juvenile hapuku (Polyprion oxygeneios)

Abstract The duration and magnitude of specific dynamic action (SDA) are largely comprised of the physiological costs of post-absorptive protein synthesis and could have a functional link to growth and feed conversion in fish. However, evidence has been found in several species to both support and oppose this hypothesis. To determine if SDA is positively linked to the production performance of a novel finfish aquaculture species, SDA was measured in juvenile hapuku Polyprion oxygeneios at two temperatures with two different ration sizes (i.e. 15 °C with a 0.75% and 1.5% body weight ration and 21 °C with a 1.5% and 3% body weight ration) and compared to the specific growth rate (SGR) and feed conversion ratio (FCR) of hapuku raised for 6 weeks at the same levels of temperature and ration size. A marked effect of temperature on SDA was found and the magnitude of SDA was significantly higher for the shared ration size (1.5% body weight) at 21 °C than 15 °C. However, only the peak of the SDA response (SDApeak) and the total energy used during the response (SDA energy) increased with ration size at both temperatures. Higher SDA parameters were linked with higher growth performance in juvenile hapuku under certain scenarios but, because SGR was significantly lower at 21 °C than 15 °C for the shared ration size of 1.5% body weight, the SDA–growth relationship was not consistent and was likely under the interactive influence of temperature and ration size. Indeed, in some scenarios higher SDA provided greater growth at 21 °C but the higher maintenance cost (i.e. MO2standard) of fish at this upper temperature may have constrained fish growth when only a 1.5% body weight ration was delivered. FCR was not positively related to SDA so this study does not support the hypothesis that SDA predicts the production performance of juvenile hapuku across a range of temperatures and ration sizes.

Effect of hypoxia on specific dynamic action and postprandial cardiovascular physiology in rainbow trout (Oncorhynchus mykiss)

Fish routinely encounter hypoxic environments, which may have detrimental effects on digestion and performance. The present study measured oxygen consumption (MO2), gastrointestinal blood flow (GBF), cardiac output (Vb) and heart rate (fH) in rainbow trout Oncorhynchus mykiss at 10°C–11.5°C while exposed to a 1.5-h step-wise hypoxia treatment (80%, 60% and 40% saturation=16.7, 12.6 and 8.4 kPa, respectively), which began 4h after being fed 1% of their body mass. GBF and fH significantly decreased by 41 and 25%–29%, respectively, at the most severe hypoxia step (40% saturation), while MO2 and Vb were maintained throughout the entire hypoxia exposure. Thus, GBF and fH were more sensitive to hypoxia than MO2 or Vb in digesting rainbow trout. Subsequent to the hypoxic exposure, the fish were returned to normoxia and monitored for a total of 50h after feeding. While the magnitude of SDA was unaffected, peak postprandial MO2 was reduced by 17%, and the duration of specific dynamic action (SDA) was prolonged by 6h in hypoxia-treated fish when compared to control fish. In conclusion, digestive performance was compromised both during and after the hypoxic exposure, which could lead to negative effects on growth.

Effects of macronutrient composition on specific dynamic action in the laboratory mouse, <i>Mus musculus</i>

Open-flow respirometry was used to measure the magnitude of specific dynamic action (SDA), the maximum rate of oxygen consumption and the length of time that the rate of oxygen uptake remained elevated above pre-feeding level in MF1 female mice fed different macronutrient diets. Irrespective of diet, the metabolic rate increased immediately after feeding and reached a maximum within 1.7 hours. The composition of the diet significantly altered the magnitude of SDA. SDA was highest for high protein-fed mice (9.4%), followed by high carbohydrate-fed mice (6.1%) and lastly high and medium fat-fed mice (3.9% and 4.5%).KEY WORDS: Specific dynamic action, resting metabolic rate, macronutrient diets, open-flow respirometry, respiratory quotient, energy expenditure

The energetic consequence of specific dynamic action in southern bluefin tunaThunnus maccoyii

The effect of feeding on the rate of oxygen consumption (M(O2)) of four groups of three southern bluefin tuna Thunnus maccoyii (SBT) was examined in a large static respirometer at water temperatures of 18.2-20.3 degrees C. Six feeding events of rations between 2.1-8.5% body mass (%M(b)) of Australian sardines (Sardinops neopilchardus) were recorded (two of the groups were fed twice). Before feeding, fish swam between 0.71 and 1.4 body lengths s(-1) (BL s(-1)) and the routine metabolic rate (RMR) was 366+/-32.5 mg kg(-1) h(-1) (mean +/- s.e.m.). For all trials, M(O2) was elevated post feeding, presumably as a result of specific dynamic action (SDA). Swimming velocity was also elevated post feeding for periods similar to that of M(O2) (between 20-45 h, longest for the largest rations). Post feeding swimming velocity increased to between 0.87-2.6 BL s(-1) and was also dependent on ration consumed. It is suggested that the purpose of increased post-feeding swimming velocity was to increase ventilation volume as a response to the enhanced metabolic demand associated with SDA. Peak post-prandial M(O2) increased linearly with ration size to a maximum of 1290 mg kg(-1) h(-1), corresponding to 2.8 times the RMR. When converted to its energy equivalent, total magnitude of SDA was linearly correlated with ration size to a maximum of 192 kJ kg(-1) h(-1), and as a proportion of gross energy ingested (SDA coefficient), it averaged 35+/-2.2%. These results demonstrate that, although the factorial increase of SDA in SBT is similar to that of other fish species, the absolute energetic cost of SDA is much higher. These results support the contention that tuna are energy speculators, gambling high rates of energy expenditure for potentially higher rates of energy returns. The ration that southern bluefin tuna require to equal the combined metabolic costs of SDA and RMR is estimated in this study to be 3.5%M(b) of Australian sardines per day.

The energetics of Calanus euxinus: locomotion, filtration of food and specific dynamic action

The effect of locomotor activity on respiration rate was studied in the food-deprived copepod Calanus euxinus tethered to a force sensor. The power generated by mouth appendages during cruising locomotion, with a frequency of 40 Hz, accounted for 0.026 and 0.0031 W for metabolic and mechanical processes, respectively. To overcome total hydrodynamic drag during foraging with a mean swimming speed of 3.2 cm s -1 , the copepods need 0.4 10 -3 W, equating to 1.3% of total metabolism. The losses of mechanical energy for body propulsion amounted to 1.3 10 -3 W, whilst the cost of feeding current generation run up to 1.8 10 -3 W, or 58% of the total. Changing of locomotor activity and respiration rate during feeding was examined separately in tethered and free-swimming copepods. At algal concentration of about 300 µgC L -1 the magnitude of specific dynamic action (SDA) averaged 1.2±0.44 nL O2 µgC -1 h -1 in copepodites V and females, with similar moving activity before and during feeding. The contribution of SDA into total metabolism varied from 23 to 85% in C. euxinus with low activity level and constituted only 10% in active animals. In starved copepods, with low locomotor activity, feeding events stimulated the increase in frequency and total duration of locomotion which resulted in elevated energy expenditure enhancing the “apparent SDA”.

Ratio Representations of Specific Dynamic Action (Mass‐Specific SDA and SDA Coefficient) Do Not Standardize for Body Mass and Meal Size

Specific dynamic action (SDA) is generally defined as the total energy expenditure associated with digestion and assimilation of ingested food and related biosynthesis (Brody 1945; Kleiber 1961). Contributing factors to SDA include secretion of digestive materials into the gastrointestinal tract, energy expended in peristalsis, upregulation and growth of relevant organs, costs of active transport, and energetic cost of intermediary metabolism and growth (Lusk 1931; Wilhelmj et al. 1931; Tandler and Beamish 1979; Wieser 1994; Secor and Diamond 2000; Starck and Beese 2001). Studies of SDA have classically focused on the role of cost of digestion in affecting potential for growth and reproduction (Brody 1945; Kleiber 1961) and on mechanisms producing SDA (Lusk 1931; Wilhemj et al. 1931). More recently, investigators have shifted some attention to the ecological and evolutionary determinants of the magnitude of SDA (Secor and Nagy 1994; Secor and Diamond 1995, 2000; Andrade et al. 1997; Secor 2001; Starck and Beese 2001; Overgaard et al. 2002). Notably, sufficient data now exist for some groups of organisms (e.g., snakes) to investigate specific hypotheses in a phylogenetic context (Secor and Diamond 2000; Secor 2001). Clearly, the present and future value of these studies finds its foundation in the methods used to represent and analyze SDA. SDA manifests itself as an increase in metabolic rate following feeding that, in some species, may last for several days. Researchers have quantified SDA using several variables, including peak metabolic rate following feeding, time to peak metabolic rate, duration of elevated metabolism, factorial scope (peak

Specific dynamic action and carbon incorporation in Calanus finmarchicus copepodites and females

Specific dynamic action (SDA) and incorporation of carbon into protein, lipids, and polysaccharides were measured in copepodite CV and adult female Calanus finmarchicus during the spring/summer growth season in Raunefjorden, Norway. Organic carbon from the food ( Rhodomonas baltica) was allocated differently in the two developmental stages. Copepodites incorporated 50–80% of the carbon into lipids and only 7–22% into protein. Carbon incorporation into protein was higher in females, constituting 23% in May at 7 °C and 34% in June at 11 °C. This resulted in significant differences in the magnitude of SDA, measured as the increase in oxygen consumption during and after an 8-h feeding event. On average, the rate of carbon incorporation into protein was 2 times higher and the magnitude of SDA was 2.5 times higher in females than in copepodites. There was a significant correlation between the magnitude of SDA and carbon incorporation into protein suggesting that SDA is linked to protein synthesis. When comparing ATP equivalents of the magnitude of SDA with ATP equivalents of the total amount of carbon incorporated, more energy was produced than consumed. This supports speculations of an energy demand associated with a rapid turnover of newly synthesised protein.

Influence of two different green algal diets on specific dynamic action and incorporation of carbon into biochemical fractions in the copepod Acartia tonsa

Previous studies have shown that the two green algae Tetraselmis sp. (Prasinophyceae) and Dunaliella tertiolecta (Chlorophyceae) induce high and low egg production rates in Acartia tonsa. The primary goal of the present study was to investigate if this is attributable to differences in the specific dynamic action (SDA) of the two diets. Secondly, we wanted to investigate if any qualitative differences in the incorporation of nutritional constituents from the two diets are influencing SDA. The functional response of ingestion was very different with the two diets. Ingestion of T. impellucida was relatively high even at low food concentrations with a maximum of 19 μg C ind -1 day -1 . The functional response was more clearly sigmoidal on D. tertiolecta with a maximum of 7.3 μg C ind -1 day -1 . The higher ingestion rate of T impellucida also induced higher respiration rates. Maximum respiration rates were 3.0 nl O 2 ind -1 min -1 on T. impellucida and 1.5 nl O 2 ind -1 min -1 on D. tertiolecta. This created significantly different SDA coefficients: 0.19 on T. impellucida and 0.06 on D. tertiolecta, which implies that the magnitude of SDA is strongly influenced by the composition of the diet. The incorporation of carbon into lipids was significantly higher on D. tertiolecta. However, because of lack of longer chain fatty acids in D. tertiolecta the copepods did not benefit from this. Thus, the proportion of carbon allocated to egg lipids was much lower than when feeding on T impellucida. Acartia tonsa incorporated relatively more carbon into proteins when feeding on T impellucida than on D. tertiolecta. Since protein synthesis is energetically very demanding this is probably the reason for the higher SDA coefficient in those feeding on T. impellucida.

Relationship between specific dynamic action and protein deposition in calanoid copepods.

The link between specific dynamic action (SDA) and protein deposition was investigated in copepodites stage V of two calanoid copepod species, the neritic Acartia tonsa and the oceanic Calanus finmarchicus. This was done by measuring respiration before, during, and after a specific feeding period and measuring the incorporation of carbon into proteins. These were also measured on individuals incubated with cycloheximide, an antibiotic that inhibits protein synthesis. The cycloheximide treatment significantly diminished the magnitude of SDA in both A. tonsa and C. finmarchicus, and inhibited carbon incorporation into protein in both species. This provides evidence that the rate at which protein deposition takes place greatly affects the magnitude of SDA. The specific respiration rates of both starving and feeding copepods were generally higher in A. tonsa than in C. finmarchicus. This influenced SDA, the magnitude of SDA normalised to an 8 h feeding period being threefold higher in A. tonsa (78.7+/-25.7 nlO(2) µgC(-1)) than in C. finmarchicus (27.5+/-11.6 nlO(2) µgC(-1)). This difference may arise due to differences in energy allocation in the organisms of the copepodite V stage of the two species. In this stage C. finmarchicus deposits large quantities of storage lipids, predominately wax esters, whereas A. tonsa deposits proteins during somatic growth.

Specific dynamic action and feeding metabolism in common carp, Cyprinus carpio L.

1. 1. Oxygen uptake attributable to Specific Dynamic Action (SDA) was measured in common carp, Cyprinus carpio L. (63.6–84.0 g) fed on 20, 35 and 50% dietary protein at 0.40 to 1.00% ration levels at 28°C. 2. 2. After feeding both SDA magnitude and mean peak oxygen consumption increased directly with dietary protein and ration levels. SDA duration was not significantly related to dietary protein but significantly increased with ration levels. 3. 3. SDA coefficients were 8.99, 13.51 and 15.94% with 20, 35 and 50% dietary protein showing a direction relationship to the protein content. The SDA coefficient did not change with ration size. 4. 4. SDA models resulting from this work are of great interest for the aquaculturist, as post-feeding oxygen requirements in an intensive fish culture can be predicted where dietary protein and ration levels are known.

The effects of dietary protein content, lipid content and ration level on oxygen consumption and specific dynamic action in oreochromis niloticus L

1. 1. The effects of dietary protein, lipid levels and ration level on oxygen consumption and specific dynamic action (SDA) were measured in Oreochromis niloticus using computer-controlled metabolic chambers. Oxygen consumption, SDA coefficient and SDA magnitude increased notably with increasing dietary protein content. 2. 2. The effect of dietary lipid, however, was shown to be virtually absent in tilapia, in contrast to some other fish species. 3. 3. Ration size had no effect on SDA coefficient but did increase oxygen consumption by up to 2.4 times over a long period. 4. 4. These data enable the prediction of peak levels of oxygen consumption and the duration of the effect if diet type and intake are known. 5. 5. Such predictive models have clear utility in production design and management. 6. 6. In addition, the regression equations derived are useful in estimating energy losses due to SDA both in practical aquaculture situations and in studies of physiological energetics.

The relationship between specific dynamic action (SDA) and growth in the common starfish, Asterias rubens L.

After feeding the metabolic rate of animals rapidly increases to a peak level and thereafter slowly declines to pre-feeding level. This phenomenon has been termed the specific dynamic action of food. The processes causing the increase in metabolism are uncertain. In Asterias rubens there was a close relationship between the magnitude of SDA and growth rate (coefficient of determination=r 2=0.85), suggesting that the increased metabolic expenditure following feeding represent the energetic cost of growth.

PROTEIN UTILIZATION IN THE FRESHWATER SHRIMP Macrobrachium rosenbergii

AbstractExperimental diets were fed to juvenile Macrobrachium rosenbergii with subsequent measurement of metabolic response in terms of oxygen consumption and nitrogen excretion. Dietary formulation was evaluated by correlating observed metabolic response with levels of protein, lipid and carbohydrate in the diet. Rates of oxygen uptake and nitrogen production were also used to quantify sparing and specific dynamic action (SDA), 2 physiological processes known to influence nutrient utilization. Comparative analysis of the magnitude of sparing and SDA as well as calculation of several closely related qualitative indices of assimilation (atomic O:N, respiratory quotient) provide a suitable means of determining the dietary formulation producing the most efficient utilization of dietary protein.Preliminary results indicate that protein influences the magnitude Of SDA in the 15–25% range of dietary protein levels; levels in excess of 25% had no effect on SDA. In addition, SDA appears to be a threshold phenomenon, operating independently on the quantity of food intake. Measurements of exogenous nitrogen excretion and corresponding O:N ratios suggest that a fat:carbohydrate ratio of 1:3‐1:4 results in more efficient utilization of dietary protein than ratios of 1:l or 1:2, which result in excessive mobilization of protein for catabolic purposes.

Specific dynamic action in premature infants kept at and below the neutral temperature.

Extract: The calorigenic effect of an artificial formula, Adapta, was examined in premature infants kept at and below the neutral temperature. After a preliminary period of 15–30 minutes, a feeding (40–60 ml) was offered or given by gavage. The test feeding was followed by an experimental period of four hours, during which time oxygen consumption and CO2 production were continuously recorded by an open circuit method using the Kipp diaferometer. The results of investigations carried out in the zone of thermoneutrality are summarized in table I. The amount of oxygen consumed 30 minutes after ingestion of the formula was already appreciably larger than that corresponding to the basal metabolic rate. At 90 or 120 minutes, the average oxygen consumption was 30% higher than that at the preliminary level. Oxygen consumption then fell and had approached the fasting level by the end of the period of observation. In order to obtain the cumulative effect of thermogenesis, total and basal heat production were calculated for a period of four hours. The average amount of total extra calories was 1.7 kcal/kg which, in relation to basal heat production during the same period of time and to the ingested calories, represented an increase of 26.4 and 9.2%, respectively (table VI). The changes in oxygen consumption at different levels of thermoregulatory heat production in totally and partially swaddled premature infants maintained at 20–22° are shown in tables II, III and IV. The responses are also diagrammatically compared (fig. 4). It can be seen that the magnitude of specific dynamic action is the same for babies in a thermoneutral and colder environment, despite the difference in the preingestion levels of oxygen consumption. Control experiments in nonfed premature infants revealed that the specific dynamic action of food in a heat-losing environment is not due to muscular activity, but appears in an additive manner and independently of the metabolic increase induced by the cold environment (table V). The summation of the metabolic response to cold and to food was also reflected by the behavior of body temperature. The ingestion of 50 ml of formula stopped the fall in body temperature and even caused a small transient rise during the period of maximum increase in heat production. Speculation: When considering the various factors upon which the zone of thermoneutrality depends, it is likely that a protein or calorie-rich feeding may constitute a significant thermal burden to premature infants cared for at neutral temperature. In contrast to thermoneutral conditions, however, the independence of the stimulating effect of food and cold on thermogenesis indicates that specific dynamic action below the critical temperature can be regarded as a useful source of heat to help maintain the body temperature in a heat-losing environment. Future studies are needed to clarify the thermoregulatory significance of postprandial thermogenesis in premature infants cared for under various environmental conditions and maintained on different feeding regimens.