Comparison of Different Approaches for the Calculation of Energy                     Expenditure Using Doubly Labeled Water in a Small Mammal

SUMMARYLimits to sustained energy intake (SusEI) are important because they constrain many aspects of animal performance. Individual variability in SusEI may be imposed by genetic factors that are inherited from parents to offspring. Here, we investigated heritability of reproductive performance in MF1 mice. Food intake, milk energy output (MEO) and litter mass were measured in mothers (F 0 ) and daughters (F 1 ) that were raising litters of 10 pups. Cross-fostering was designed so that half of each litter consisted of biological offspring and the rest came from one unrelated female (i.e. fostered pups). Food intake increased linearly during early lactation and reached a plateau during late lactation (day 9-13, called the asymptotic food intake, FI AS , equivalent to SusEI). Parent-offspring regression showed that FI AS , MEO and litter mass were all positively and significantly related between mothers and their biological daughters, but no significant relationships were found between the same traits for mothers and fostered daughters. FI AS at peak lactation was significantly correlated to adult food intake and body mass when the mice were 6months old and not lactating. In conclusion, a large part of the variation in FI AS could be explained by genetic variation or maternal effects in pregnancy whereas non-genetic maternal effects in lactation were negligible. As a consequence, biological daughters of mothers with high reproductive performance (i.e. high milk production and hence higher litter mass at weaning) had a better reproductive performance themselves, independent of the mother that raised them during lactation.

Section: Methodsmentioning

confidence: 99%

Section: Deementioning

confidence: 99%

Limits to sustained energy intake. XIV. Heritability of reproductive performance in mice

Vaanholt

Sinclair

Speakman

2013

“…Whole-blood samples were pipetted into 0.7 ml glass vials and stored at 5°C until determination of 18 O and 2 H enrichment. Blood samples were vacuum distilled (Nagy, 1983), and water from the resulting distillate was used to produce CO 2 and H 2 [see Speakman et al (Speakman et al, 1990) for CO 2 and Speakman and Krol (Speakman and Krol, 2005) 1 H were analysed using gas source isotope ratio mass spectrometry (Isochrom μG and Isoprime, respectively, Micromass Ltd, Manchester, UK). Samples were run alongside five lab standards for each isotope (calibrated to the IAEA International Standards: SMOW and SLAP) to correct delta values to ppm.…”

Section: Fmrmentioning

confidence: 99%

Saving energy during hard times: Energetic adaptations of Shetland pony mares

Brinkmann

Gerken

Hambly

et al. 2014

Recent results suggest that wild Northern herbivores reduce their metabolism during times of low ambient temperature and food shortage in order to reduce their energetic needs. It is, however, not known whether domesticated animals are also able to reduce their energy expenditure. We exposed 10 Shetland pony mares to different environmental conditions (summer and winter) and to two food quantities (60% and 100% of maintenance energy requirement) during low winter temperatures to examine energetic and behavioural responses. In summer, ponies showed a considerably higher field metabolic rate (FMR; 63.4±15.0 MJ day −1 ) compared with foodrestricted and control animals in winter (24.6±7.8 and 15.0±1.1 MJ day −1 , respectively). During summer, locomotor activity, resting heart rate and total water turnover were considerably elevated (P<0.001) compared with winter. Animals on a restricted diet (N=5) compensated for the decreased energy supply by reducing their FMR by 26% compared with control animals (N=5). Furthermore, resting heart rate, body mass and body condition score were lower (29.2±2.7 beats min −1 , 140±22 kg and 3.0±1.0 points, respectively) than in control animals (36.8±41 beats min −1 , 165±31 kg, 4.4±0.7 points; P<0.05). While the observed behaviour did not change, nocturnal hypothermia was elevated. We conclude that ponies acclimatize to different climatic conditions by changing their metabolic rate, behaviour and some physiological parameters. When exposed to energy challenges, ponies, like wild herbivores, exhibited hypometabolism and nocturnal hypothermia.

“…Previous work has indicated the accuracy of this method to measure DEE in small mammals (Speakman and Król, 2005b). Measurements were made across 2 days to minimise the potential day-today variability in DEE (Speakman et al, 1994;Berteaux et al, 1996).…”

Section: Deementioning

confidence: 99%

“…Two days after dosing, a final blood sample was collected as close as possible to 48 h after the initial sample to minimise circadian effects (Speakman and Racey, 1988b). Capillaries containing the blood samples were then distilled using a vacuum (Nagy, 1983) and the produced water was used to generate CO 2 (Speakman et al, 1990) or H 2 (Speakman and Król, 2005b). The isotope ratios 18 O: 16 O in CO 2 and 2 H: 1 H in H 2 were analysed using gas source isotope ratio mass spectrometry (ISOCHROMμGAS system and IsoPrime IRMS, Micromass, Manchester, UK).…”

Section: Deementioning

confidence: 99%

Limits to sustained energy intake. XXII. Reproductive performance of two selected mouse lines with different thermal conductance

Jothery

Król

Hawkins

et al. 2014

Self Cite

Maximal sustained energy intake (SusEI) appears limited, but the factors imposing the limit are disputed. We studied reproductive performance in two lines of mice selected for high and low food intake (MH and ML, respectively), and known to have large differences in thermal conductance (29% higher in the MH line at 21°C). When these mice raised their natural litters, their metabolisable energy intake significantly increased over the first 13 days of lactation and then reached a plateau. At peak lactation, MH mice assimilated on average 45.3% more energy than ML mice (222.9±7.1 and 153.4±12.5 kJ day −1 , N=49 and 24, respectively). Moreover, MH mice exported on average 62.3 kJ day −1 more energy as milk than ML mice (118.9±5.3 and 56.6±5.4 kJ day, N=subset of 32 and 21, respectively). The elevated milk production of MH mice enabled them to wean litters (65.2±2.1 g) that were on average 50.2% heavier than litters produced by ML mothers (43.4±3.0 g), and pups that were on average 27.2% heavier (9.9±0.2 and 7.8±0.2 g, respectively). Lactating mice in both lines had significantly longer and heavier guts compared with non-reproductive mice. However, inconsistent with the 'central limit hypothesis', the ML mice had significantly longer and heavier intestines than MH mice. An experiment where the mice raised litters of the opposing line demonstrated that lactation performance was not limited by the growth capacity of offspring. Our findings are consistent with the idea that the SusEI at peak lactation is constrained by the capacity of the mothers to dissipate body heat.