Milk energy output during peak lactation in shaved Swiss mice

Understanding factors limiting sustained metabolic rate (SusMR) is a central issue in ecological physiology. According to the heat dissipation limit (HDL) theory, the SusMR at peak lactation is constrained by the maternal capacity to dissipate body heat. To test that theory, we shaved lactating bank voles (Myodes glareolus) to experimentally elevate their capacity for heat dissipation. The voles were sampled from lines selected for high aerobic exercise metabolism (A; characterized also by increased basal metabolic rate) and unselected control lines (C). Fur removal significantly increased the peak-lactation food intake (mass-adjusted least square means±s.e.; shaved: 16.3±0.3 g day ; P<0.0001), average daily metabolic rate (shaved: 109± 2 kJ day ; P=0.028). Thus, fur removal increased both the total energy budget and reproductive output at the most demanding period of lactation, which supports the HDL theory. However, digestive efficiency was lower in shaved voles (76.0±0.3%) than in unshaved ones (78.5±0.2%; P<0.0001), which may indicate that a limit imposed by the capacity of the alimentary system was also approached. Shaving similarly affected the metabolic and reproductive traits in voles from the A and C lines. Thus, the experimental evolution model did not reveal a difference in the limiting mechanism between animals with inherently different metabolic rates.

Section: Discussionmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Limits to sustained energy intake. XXIII. Does heat dissipation capacity limit the energy budget of lactating bank voles?

Sadowska

Król

Chrząścik

et al. 2016

“…We have previously repeated the shaving experiment of Król and colleagues (Król et al, 2007) on Swiss mice according to the same protocol with that performed on MF1 mice, and found that fur removal had an effect on food intake but although the effect on pup growth was in the expected direction it was not statistically significant (Zhao and Cao, 2009;Zhao et al, 2010a). These data were different from those observed in MF1 mice, and provided support for the peripheral limitation hypothesis.…”

Section: Introductionmentioning

confidence: 78%

“…For MF1 mice, the ability to dissipate heat might be below the maximum milk production capacity, and hence when the ability to dissipate heat was elevated by exposure to cold, milk production was increased . In contrast, when heat dissipation capacity was increased by cold exposure in Swiss mice, they failed to upregulate milk production because their maximal milk production capacity was lower, relative to their capacity to dissipate heat (Zhao and Cao, 2009;Zhao et al, 2010a;Speakman and Król, 2011). An alternative hypothesis, however, is that milk production in Swiss mice is regulated by pup growth capacity.…”

Section: Introductionmentioning

confidence: 99%

Limits to sustained energy intake. XVIII. Energy intake and reproductive output during lactation in Swiss mice raising small litters

Zhao

Song

et al. 2013

Self Cite

SUMMARYLimits to sustained energy intake (SusEI) during lactation in Swiss mice have been suggested to reflect the secretory capacity of the mammary glands. However, an alternative explanation is that milk production and food intake are regulated to match the limited growth capacity of the offspring. In the present study, female Swiss mice were experimentally manipulated in two wayslitter sizes were adjusted to be between 1 and 9 pups and mice were exposed to either warm (21°C) or cold (5°C) conditions from day 10 of lactation. Energy intake, number of pups and litter mass, milk energy output (MEO), thermogenesis, mass of the mammary glands and brown adipose tissue cytochrome c oxidase activity of the mothers were measured. At 21 and 5°C, pup mass at weaning was almost independent of litter size. Positive correlations were observed between the number of pups, litter mass, asymptotic food intake and MEO. These data were consistent with the suggestion that in small litters, pup requirements may be the major factor limiting milk production. Pups raised at 5°C had significantly lower body masses than those raised at 21°C. This was despite the fact that milk production and energy intake at the same litter sizes were both substantially higher in females raising pups at 5°C. This suggests that pup growth capacity is lower in the cold, perhaps due to pups allocating ingested energy to fuel thermogenesis. Differences in observed levels of milk production under different conditions may then reflect a complex interplay between factors limiting maternal performance (peripheral limitation and heat dissipation: generally better when it is cooler) and factors influencing maximum pup growth (litter size and temperature: generally better when it is hotter), and may together result in an optimal temperature favouring reproduction.

“…the alimentary tract (Hackländer, 2002;Hammond et al, 1994;Perrigo, 1987;Speakman and Król, 2005a), while the 'peripheral limitation hypothesis' states that the limit is imposed peripherally by the energy-consuming machinery, e.g. the muscles or the mammary glands (Hammond et al, 1996;Zhao and Cao, 2009;Zhao et al, 2010). More recently, the 'heat dissipation limit theory' has been proposed, which suggests that animals may be limited by the capacity to dissipate heat generated as a by-product of processing food and producing milk (Król and Speakman, 2003a;Król et al, 2007;Speakman and Król, 2010;Speakman and Król, 2011).…”

Section: Introductionmentioning

confidence: 99%

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

Vaanholt

Sinclair

Speakman

2013

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.