Degradation of two soluble proteins – casein and egg protein by a macro in vitro method

Degradation of casein and egg protein was studied with whole rumen contents (RC) in a macro in vitro system to elucidate previous findings of initial rapid disappearance of soluble proteins in vitro. Five to 7.5 kg of RC from a dry and/or a lactating cow were incubated with buffer and casein or egg protein for 180 min with frequent sampling. Degradation was measured as loss of trichloroacetic acid precipitable N (TCA‐N) from the inocula. Normal (39 °C) and low (2 °C) temperature incubations were examined in Exp. 1, using 1 g of TCA‐N from casein. Four levels of casein (0–12 g TCA‐N) in Exp. 2 and four levels of egg albumin (0–24 g TCA‐N) in Exp. 3 were fermented at 39 °C. Initial recovery of casein TCA‐N was 106% at 2 °C and 56% at 39 °C (Exp. 1). Casein (TCA‐N) recovered initially increased in Exp. 2 from 21% at 3 g to 86% at 12 g TCA‐N, while absolute loss remained relatively constant at 358 mg TCA‐N/kg RC (SD = 47). Fractional degradation rate was highest (0.03/min) at the intermediate dosage level. In the absence of rumen fluid (Exp. 4), no casein was lost. Initial egg protein recovery was on average 103% (Exp. 3). Recovery seemed unaffected by dosage level, and absolute degradation rate was relatively constant over time and increased with dosage level (p < 0.001) from 1.48 to 2.95 mg TCA‐N/(kg RC × min). Maximum degradation rate [mg TCA‐N/(kg RC × min)] and affinity constant (mg TCA‐N/kg RC) were estimated at 261 and 1650, respectively. It is concluded that a surprisingly constant amount of casein disappears immediately from warm rumen fluid and that this does not occur either with chilled RC, in the absence of rumen fluid, or when replaced with egg protein. The mechanisms for this disappearance are yet to be discovered.     

Temperature determines the shift of thermal neutral zone and influences thermogenic capacity in striped hamsters

The thermoneutral zone (TNZ) reflects the adaptation of mammals to their natural habitat. However, it remains unclear how TNZ shifts in response to variations in ambient temperature. To test the hypothesis that ambient temperature plays a key role in determining TNZ variations between seasons, we measured metabolic rate, body temperature, and cytochrome c oxidase (COX) activity of several visceral organs in striped hamsters (Cricetulus barabensis) either acclimated to semi-natural conditions over a year, or subjected to a gradual decrease in mean temperature from 30 ± 1°C to −15 ± 1°C. The TNZ range in striped hamsters differed seasonally, with a wider TNZ and a lower lower-critical temperature in winter compared to summer. The hamsters showed a considerable leftward shift of lower-critical temperature from 30°C to 20°C after the ambient temperature of acclimation from 30°C down to −15°C, whereas the upper-critical temperature of TNZ remained fixed at 32.5°C. The resting metabolic rate in thermoneutral zone (RMRt), nonshivering thermogenesis (NST), and COX activity of brown adipose tissue, liver, skeletal muscle, brain, and kidneys, increased significantly in hamsters acclimated at lower ambient temperatures. Following acute exposure to 5°C and −15°C, hamsters acclimated to 32.5°C had significantly lower maximal NST and lower serum thyroid tri-iodothyronine (T₃) levels compared to those kept at 23°C. These findings suggest that acclimation to the upper-critical temperature of TNZ impairs the hamsters’ thermogenic capacity to cope with extreme cold temperature. Reduced ambient temperature was mainly responsible for the leftward shift of TNZ in striped hamsters, which reflects the adaptation to cold environments.     

The effects of wilting and storage temperatures on the fermentation quality and aerobic stability of stylo silage

In order to clarify the ensiling characteristics of stylo (Stylosanthes guianensis Swartz), the effects of wilting (no wilting, light wilting and heavy wilting) and storage temperatures (10°C, 20°C, 30°C and 40°C) on the fermentation quality and aerobic stability of stylo silage were investigated. Wilting had no significant influence on the contents of crude protein, ether extract and acid detergent fiber, and numbers of lactic acid bacteria, aerobic bacteria, yeasts and mold (P > 0.05). Heavy wilted material, wilted for 12 h, had higher neutral detergent fiber content and lower water‐soluble carbohydrate content than unwilted and light wilted materials (P < 0.05). Wilting and storage temperatures had significant effects on pH value, acetic acid, butyric acid and NH₃‐N contents of stylo silage (P < 0.01 or P < 0.05). Wilting tended to reduce acetic acid and NH₃‐N contents and improve the fermentation quality of stylo silage. In all the silages, no wilting silage ensiled at 30°C had the highest butyric acid content (P < 0.05). High temperature of 40°C markedly restricted the growth of lactic acid bacteria and aerobic bacteria in silage, irrespective of wilting. The wilted silage or silage stored at low temperature had poor aerobic stability.     

Effects of heat exposure on nutrient digestibility, rumen contraction and hormone secretion in goats

The present study investigated changes in nutrient digestibility, rumen fermentation, behavior and hormone (growth hormone (GH), insulin and insulin‐like growth factor‐1 (IGF‐1)) secretion among goats (three male goats) in a hot environment (H, 35 ± 1.2°C; relative humidity (RH), 80 ± 7.2%; 13 days), in a thermoneutral environment (T, 20 ± 0.6°C; RH, 80 ± 3.4%; 20 days), and in a thermoneutral environment accompanied by the same restricted diet as provided in the hot environment (TR, 20 ± 0.6°C; RH, 80 ± 3.4%; 20 days). The following results were obtained: rectal temperature and water intake were higher in the H treatment than in the T treatment or TR treatment, while hay consumption was lower. Crude protein, neutral detergent fiber and acid detergent fiber digestibility was highest in H treatment. The concentrations of acetic acid and butyric acid in the rumen was also highest in the H treatment. Time spent eating in the H treatment was also the highest, followed in order by T treatment and TR treatment. Ruminating time was lower in H treatment than in T treatment or TR treatment, and reposing time was highest in the TR treatment. When eating and ruminating, the amplitude values of the rumen contraction were lowest in the H treatment, as was the frequency of rumen contraction. Excretion of plastic particles was faster in T treatment and TR treatment than H treatment. Heat exposure was associated with world lowered concentrations of total volatile fatty acids and acetic acid in plasma. The plasma glucose concentration was highest in the T treatment, followed in order by TR treatment and H treatment. The plasma GH concentration was lowest in the H treatment, while the plasma insulin was highest in the H treatment. The IGF‐1 concentration was highest in the H treatment, followed in order by T treatment and TR treatment. In conclusion, heat exposure in goats decreased feed intake and rumen contraction, but increased digestibility. However, when goats in a thermoneutral environment received the same restricted feeding as they received in the hot environment, digestibility increased without a change in rumen contraction. Between the H treatment and TR treatment, the changes in digestibility were accomplished by coordinate changes in hormone secretion in order to maintain body homeostasis.     

Effect of xylazine in heifers under thermoneutral or heat stress conditions

A study was performed to assess the effect of xylazine HCl (0.1 mg/kg of body weight, IV) in heifers maintained at thermoneutrality (18 C, 42% humidity) or under heat stress (33 C, 63% humidity) conditions. Xylazine caused 50 and 70% decreases in serum insulin concentrations in the thermoneutral and heat-stressed heifers, respectively. Xylazine-induced hypoinsulinemia was associated with hyperglycemia. In the thermoneutral group, serum glucose concentrations increased from a basal concentration of 75 mg/dl to 150 mg/dl after 15 minutes. In the heat stress group, the serum glucose concentration increased from 65 mg/dl to 105 mg/dl. Hyperglycemia peaked at 2 hours and remained high for 6 hours after xylazine administration. Heat-stressed heifers took a longer time (107 minutes) to stand than did heifers under thermoneutral conditions (41 minutes). The time to regain sensation to pain was significantly prolonged in heat-stressed heifers. Xylazine had no effect on body temperature and respiration rate in heifers under the thermoneutral condition, whereas it markedly induced hyperthermia and suppressed respiration rate in the heat-stressed heifers. Furthermore, the pulse rate was slightly decreased in thermoneutral heifers and was markedly decreased in the heat-stressed heifers.     

The period of adaptation of the fasting metabolic rate of the common fowl to an increase in environmental temperature from 22 degrees C to 28 degrees C

The period of time required by fasting fowls to adjust their metabolic rate following an increase in environmental temperature was investigated using respiration calorimetry.

A significant decrease in the fasting metabolic rate of White Leghorn hens and Light Sussex cockerels was observed following increasing the environmental temperature from 22° C to 28° C. No significant decline in the fasting metabolic rate of the hens occurred during the first 3 d at the higher temperature. After 12 d no further decline occurred, indicating that the period of adaptation was between 3 and 12 d. In the cockerels no significant decline had occurred by the 7th day, but after 28 d the adaptation of metabolic rate was complete. The importance of these results in relation to the assessment of the thermoneutral zone of the fowl and the role of the thyroid secretion in acclimatisation in the fowl are discussed.     

Effect of resveratrol on growth performance,rectal temperature and serum parameters of yellow‐feather broilers under heat stress

This study investigated the effect of dietary resveratrol supplementation on growth performance, rectal temperature, and serum parameters of yellow‐feather broilers under heat stress. A total of 480 yellow‐feather broilers (28‐day‐old) were randomly allotted to five groups with six replicates. A thermoneutral group (TN) (24 ± 2°C) received a basal diet and another four heat‐stressed groups (37 ± 2°C for 8 hr/day and 24 ± 2°C for the remaining time) were fed the basal diet or basal diet with 200, 350, and 500 mg/kg resveratrol for 14 consecutive days. The results revealed that resveratrol supplementation improved average daily gain (p = 0.001), and decreased (p < 0.05) rectal temperature from d 3 when compared with heat‐stressed group without resveratrol. In addition, supplementation with resveratrol at 350 or 500 mg/kg lowered (p < 0.05) the contents of corticosterone, adrenocorticotropic hormone, cholesterol, triglycerides, uric acid, malonaldehyde, and activities of aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase, increased (p < 0.05) the levels of triiodothyronine, the ratio of triiodothyronine to thyroxine, total protein, glutathione, and activities of alkaline phosphatase, total superoxide dismutase, catalase, and glutathione peroxidase, though with few fluctuation. In conclusion, supplementation with resveratrol can improve the growth performance by positively regulating serum metabolic parameters and alleviating tissue oxidant damage of broilers under heat stress.     

Rectal temperature responses of donkeys administered with ascorbic acid and subjected to load carrying (packing) during the harmattan season in Nigeria

The aim of the experiment was to evaluate the effect of 4-h load carrying (packing) on donkeys administered with ascorbic acid (AA) during the harmattan season. Six donkeys administered orally with ascorbic acid (200 mg/kg) and subjected to packing served as experimental animals, while six others given only distilled water served as control animals. The rectal temperature (RT) of each donkey and dry-bulb temperature (DBT) and relative humidity (RH) of the research pen were recorded at 0600 hours pre-packing; while post-packing, the values were obtained at 1430, 1600 and 1800 hours. The DBT values (ranges) recorded before, during and after packing were 13.7?±?1.3 °C (11–15 °C), 28.4?±?1.0 °C (22.7–30.3 °C) and 30.6?±?3.0 °C (19.8–45 °C), respectively. The highest temperature–humidity index (THI) of 83.4?±?6.9 was obtained at 1430 hours after packing, and the value decreased to 64.2?±?5.8 at 1800 hours. The thermal environmental conditions were outside the thermoneutral zone for the donkeys. The RT values recorded immediately after packing did not differ (P?>?0.05) in experimental and control donkeys; but at 1600 and 1800 hours, values obtained in control donkeys (38.48?±?0.12 and 38.12?±?0.12 °C, respectively) were significantly higher (P?<?0.05) than those recorded in experimental donkeys (38.16?±?0.14 and 37.85?±?0.14 °C, respectively). In conclusion, administration of ascorbic acid reduced the rise in RT due to packing and may be of value in the amelioration of adverse effects of heat stress associated with work in donkeys.     

The effects of temperature on the silage microbiology and aerobic stability of corn and vetch-grain silages

Abstract

The purpose of the current work was to extend the study of the effect of temperature on silage microbiology, with or without formic acid, and on the aerobic stability of corn and vetch-grain silages.

The silage samples were ensiled in 1.0-l anaerobic jars, with and without formic acid, at room (20°C) or elevated temperatures (30–37°C). After 45 days of ensiling, the silages were subjected to an aerobic stability test at room (20°C) and elevated (30–37°C) temperatures. The most intensive deterioration occurred at 30–37°C. Samples incubated at 30–37°C had the highest yeast and mould count, most prolific CO₂ production.

The finding of the current study suggests that formic acid may decrease mould growth in silage samples. Unfortunately, formic acid does not reduce aerobic deterioration rate of silages. Applying a 5 g/kg formic acid on corn and vetch-grain silages was not very effective at high temperatures.     

Inter‐group associations in Mongolian gerbils: Quantitative evidence from social network analysis

Animals often interact non‐randomly with conspecifics, and association preferences can differ across life‐history stages to maximize individuals' fitness. Mongolian gerbils (Meriones unguiculatus) are a social rodent that live in highly seasonal habitats and display seasonal fluctuations in population density, growth rate and the size of overlapped home ranges. Nevertheless, whether gerbils modify their social relationships at different life‐history stages remains unknown. Here, we used social network analysis to examine whether social associations differ between the sexes and between life‐history stages in a wild population of Mongolian gerbils. We quantified social attributes at both group level (assortativity) and individual level (social differentiation and degree, closeness and betweenness centrality); these attributes reflect individuals' social preferences and their potential influence on others in the network. We found that both male and female gerbils established fewer inter‐group social connections during the food‐hoarding season than during the breeding season, revealing constraints on sociality. Similarly, during the food‐hoarding season, degree centrality and social differentiation increased significantly whereas closeness and betweenness centrality decreased significantly. Together, these results suggest that gerbils have relatively more partners and preferred associations and decreased influence over others in the network during the food‐hoarding season. In addition, we found no significant difference in any of the social attribute between males and females, but there was a significant interaction effect between sex and season on degree, closeness and betweenness centrality. Our results demonstrate that Mongolian gerbils adjust their association strategies to adapt to the changes of life history. Such adjustments may balance the costs/benefits associated with survival and reproduction.     

Effect of probiotic supplementation on growth performance,intestinal morphology,barrier integrity,and inflammatory response in broilers subjected to cyclic heat stress

This study investigated the protective effects of probiotic on heat stress‐induced intestinal injury and inflammatory response in broilers. A total of 180 male broilers were randomly allocated to three treatments with four replicates each from 22 to 42 days of age. The broilers were either raised under thermoneutral (TN) conditions (23 ± 1°C) or subjected to cyclic heat stress (28–35–28°C for 12 hr daily). The broilers kept at TN conditions were fed a basal diet, and those exposed to heat stress were fed basal diets supplemented with or without probiotic at a dose of 1.5 × 10⁸ cfu/kg. Compared with the TN group, heat stress decreased (p < .05) the growth performance, reduced (p < .05) villus height and villus height: crypt depth ratio in intestinal mucosa, increased (p < .05) serum levels of D‐lactic acid on day 28 and endotoxin, TNF‐α and IL‐6 on day 42, and decreased (p < .05) serum IL‐10 content on day 42. Dietary supplementation of probiotic reversed (p < .05) all these changes except for the growth performance in heat‐stressed broilers. In conclusion, dietary inclusion of probiotic could improve intestinal morphology and barrier function, alleviate inflammatory response, but exert no ameliorative effect on growth performance of broilers under cyclic heat stress.     

Production of a bacteriocin‐like inhibitory substance by Leuconostoc mesenteroides subsp. dextranicum 213M0 isolated from Mongolian fermented mare milk,airag

Strain 213M0 was selected with productivity of a bacteriocin‐like inhibitory substance (BLIS) among 235 strains of lactic acid bacteria (LAB) isolated from Mongolian fermented milk ‘airag’. Strain 213M0 was species‐identified as Leuconostoc mesenteroides subsp. dextranicum by morphological observation, carbohydrate fermentation profiling and sequencing the 16S rRNA gene. Incubation temperature proper to produce the BLIS was 25°C rather than 30 and 37°C, and the production actively proceeded during the exponential growth phase of the producer cells. Antibacterial effect of BLIS 213M0 was limited to all nine strains of Listeria sp. bacteria and seven strains of LAB cocci among 53 tested strains, which corresponds to a typical feature of the class IIa pediocin‐like bacteriocins. BLIS 213M0 was not inactivated in every broad pH range solution (pH 2.0‐11.0), and was stable against storage at 25°C for 1 week and heating at 121°C for 15 min under pH 4.5. Peptide frame of BLIS 213M0 was confirmed by inactivation with some peptidases, and then its molecular weight was estimated to be 2.6‐3.0 kDa using an in situ activity assay following sodium dodecyl sulfate polyacrylamide gel electrophoresis. The estimated size was different from the other Leuconostoc bacteriocins already reported. These results suggest that BLIS 213M0 would be a novel listericidal bacteriocin.     

Effect of long‐distance transportation on serum metabolic profiles of steer calves

Long‐distance transportation is sometimes inevitable in the beef industry because of the geographic separation of major breeding and fattening areas. Long‐distance transportation negatively impacts production and health of cattle, which may, at least partly, result from the disturbance of metabolism during and after transportation. However, alteration of metabolism remains elusive in transported cattle. We investigated the effects of transportation on the metabolomic profiles of Holstein steer calves. Non‐targeted analysis of serum concentrations of low molecular weight metabolites was performed by gas chromatography mass spectrometry. Transportation affected 38 metabolites in the serum. A pathway analysis suggested that 26, 10, and 10 pathways were affected immediately after transportation, and 3 and 7 days after transportation, respectively. Some pathways were disturbed only immediately after transportation, likely because of feed and water withdrawal during transit. Nicotinate and nicotinamide metabolism, and citric acid cycle were affected for 3 days after transportation, whereas propionate metabolism, phenylalanine and tyrosine metabolism were affected throughout the experiment. Four pathways were not affected immediately after transportation, but were altered thereafter. These results suggested that many metabolic pathways had marked perturbations during transportation. Metabolites such as citric acid, propionate, tyrosine and niacin can be candidate supplements for mitigating transportation‐induced adverse effects.     

水热因子对克氏针茅草原土壤呼吸及其土壤温度敏感性的影响

作为内蒙古重要的草地资源,克氏针茅草原在我国畜牧业生产中占有重要的地位。土壤呼吸是大气与陆地生态系统碳循环的主要通量,是土壤碳输出的主要途径。试验区设置在内蒙古锡林浩特市东部毛登牧场内以克氏针茅建群的典型草原;在2011-2013年采用开顶式生长室(OTC)对试验样地进行模拟增温增雨处理,在生长季(5-9月份)使用开路式土壤碳通量测量系统(LI-8100, LI-COR,NE) 对试验样地土壤呼吸强度进行测定;同时监测试验样地气温、土壤温湿度等环境因子,采集土壤样品并室内分析土壤养分特征和微生物生物量,并对土壤呼吸与环境因子间进行相关性分析。克氏针茅草原土壤呼吸受空气温度和土壤含水量影响显著(P<0.05),分别呈现出二项函数和线性相关关系;不同处理下土壤呼吸在相同时间存在显著差异(P<0.05),2012年增温增雨与增温处理下土壤呼吸速率分别为2.60和1.96 μmol/(m²·s), 2013年增温增雨与增温处理下土壤呼吸速率分别为3.38和2.09 μmol/(m²·s);增温增雨处理下,克氏针茅草原空气温度的升高和土壤含水量的降低均对土壤呼吸产生了抑制。土壤呼吸温度敏感度(Q₁₀)在2011-2012年中增温增雨处理明显高于对照处理和控温处理;2011-2013年控温处理都低于对照处理。本研究表明,土壤呼吸主要受水热条件影响,并且空气温度升高和土壤含水量的降低均对土壤呼吸有抑制作用,增温增雨处理下土壤呼吸速率要高于增温处理;土壤呼吸温度敏感系数与土壤温度、土壤含水量、土壤有机碳、全氮和微生物等环境因子之间的关系较为复杂,还有待深入研究。     

Heat production and dissipation in a South African diurnal murid Lemniscomys griselda

Heat production measured as oxygen consumption (V_O2 and heat dissipation calculated as the means of the overall thermal conductance were studied in a South African diurnal murid Lemniscomys griselda. This species maintains its body temperature (T_b) well at around 36,5 ± 1,0 °C over ambient temperatures (T_a) ranging between 5 and 34 °C. The thermoneutral zone lies between T _a = 30-34 °C. When exposed to temperatures below the low critical point L. griselda at rest conforms to Newton's law of cooling. Non-shivering thermo- genesis (NST) was studied as a response to an injection of noradrenaline (sc). Following the administration of 1,5 mg noradrenaline per kg body mass to an anaesthetized animal, an increase of 329% in VO₂ was recorded. The distribution pattern of L. griselda in comparison with that of Rhabdomys pumilio, the more common diurnal murid species in South Africa, is discussed.     

瑞香狼毒根对长爪沙鼠的急性毒力测试

本文采用含17%瑞香狼毒(Stellera chamaejasme)根粉末的毒饵,依据孙氏改良寇氏综合计算法,实验室内测定了其对长爪沙鼠(Meriones unguiculatus)的急性毒力。根据预试验结果,采用最低剂量为7.0 g·kg^-1,最适剂量梯度比值K=0.65的5个剂量梯度的瑞香狼毒根毒饵饲喂长爪沙鼠。结果显示:试验组试鼠体重明显下降(P=0.029<0.05),完全致死组肝脏重/体重比对照组明显减小(P=0.014<0.05),但肾脏略增大(P=0.102>0.05)。其对长爪沙鼠的LD50为(20.37±0.086)g·kg^-1,95%平均可信限为(20.37±7.84)g·kg^-1,属弱毒水平。     

Impairment of cellular and humoral immunity in overweight Mongolian gerbils (Meriones unguiculatus)

Animal immunity is usually impaired in obesity. We know little about the effect of being overweight or obese on the immune function of wild rodents. The present study is aimed to test the hypothesis that immunity is suppressed in overweight Mongolian gerbils (Meriones unguiculatus). In the study, 16 overweight (body mass: 90.8–127.6 g) and 16 lean gerbils (body mass: 60.5–77.7 g) were randomly selected from a total of 174 male gerbils (body mass range: 55.8–144.7 g). Half of the overweight and lean males were injected with sterile saline; the others were immunochallenged (IC) with phytohaemagglutinin and keyhole limpet hemocyanin to assess cellular and humoral immunity, respectively. Body fat mass, wet and dry spleen mass, leukocyte counts, blood glucose levels and serum leptin levels were significantly higher in the overweight gerbils than in the lean gerbils. However, phytohemagglutinin response indicative of cellular immunity and immunoglobulin G concentrations was significantly lower in the IC overweight gerbils than in the IC lean gerbils. These results indicate that cellular and humoral immunity are impaired in the overweight gerbils. Excessive body fat mass, higher leukocyte counts and serum leptin levels imply that overweight gerbils are in a low grade inflammatory state.     

Alleviative effects of α-lipoic acid supplementation on acute heat stress-induced thermal panting and the level of plasma nonesterified fatty acids in hypothyroid broiler chickens

1. The present study was conducted to examine the effects of α-lipoic acid on hypothyroidism-induced negative growth performance and whether α-lipoic acid alleviates acute heat stress in relation to hypothyroid status.

2. Female broiler chickens (14?d-old) were fed diets supplemented with α-lipoic acid (100?mg/kg) and an antithyroid substance, propylthiouracil (200?mg/kg), for 20?d under thermoneutral conditions (25°C). At 42?d of age, chickens were exposed to a high ambient temperature (36°C, 60% RH) for 4?h.

3. Under the thermoneutral condition, propylthiouracil administration decreased feed efficiency and concomitantly increased adipose tissue and thyroid gland weights. Plasma nonesterified fatty acids and triacylglycerol were also increased by propylthiouracil administration. However, α-lipoic acid supplementation did not affect the hypothyroidism-induced effects.

4. In hypothyroid chickens, the rise in respiratory rate induced by heat exposure was greatly inhibited by α-lipoic acid administration at 1?h, but this effect had disappeared at 4?h. In addition, a similar inhibitory effect on the concentrations of plasma nonesterified fatty acids was subsequently observed at 4?h.

5. Therefore, the present study suggested that α-lipoic acid alleviates acute heat stress if chickens are in a hypothyroid status.     

Ouabain-sensitive respiration and protein synthesis in duodenal mucosa and liver in rats fed increasing levels of pea fibre or protein and housed in 18 or 28°C environments

Seventy‐two Wistar rats were used in two studies to investigate the effect of environmental temperature (18 or 28°C), and increasing levels of dietary fibre (low, 68 g/kg dry matter (DM); medium 110 g/kg DM; high, 157 g/kg DM) and protein (low, 91 g/kg DM; medium, 171 g/kg DM; high, 262 g/kg DM) on respiration attributable to Na⁺,K⁺‐ATPase activity and protein synthesis in duodenal mucosa and liver of rats. In vitro O₂ consumption in tissues was measured polarographically using a Clark‐style YSI biological O₂ monitor. Whole‐body O₂ consumption was measured with two open‐circuit respiration chambers. Whole‐body O₂ consumption was higher (p < 0.05) at 18°C than at 28°C. Rats fed the low protein diet had significantly higher (p < 0.05) whole‐body O₂ consumption than those fed the medium or high protein diet. Compared with 28°C, the environmental temperature of 18°C caused an increase (p < 0.05) in total O₂ consumption and O₂ consumption attributable to Na⁺,K⁺‐ATPase activity in duodenal mucosa. There was no effect (p > 0.05) of environmental temperature on total O₂ consumption, Na⁺,K⁺‐ATPase activity attributable to protein synthesis dependent on O₂ consumption in the liver. Total O₂ consumption and O₂ consumption attributable to Na⁺,K⁺‐ATPase activity increased (p < 0.05) in duodenal mucosa in rats fed the low level of dietary fibre compared with rats fed the medium level of dietary fibre. In vitro O₂ consumption determined in duodenal mucosa and in liver did not always correspond to whole‐body O₂ consumption. This may indicate that respiration in the duodenum and liver adapts differently and may not reflect changes in whole‐body respiration in response to dietary modification and changes in thermal environment.