Thermal limitation of mother–young contact in norway rats

131

129

Section: Discussionmentioning

confidence: 70%

Limits to sustained energy intake. X. Effects of fur removal on reproductive performance in laboratory mice

Król

Murphy

Speakman

2007

131

129

“…A decreased suckling stimulus caused by continual disruption of suckling would lead to lower oxytocin, and ultimately a lower level of milk production (Croskerry et al, 1978;Speakman and Krol, 2005). Consistent with the heat dissipation limitation hypothesis, over the lactation period, maternal rats with fur removed spent more time with their pups in the nest compared with non-shaved individuals (Croskerry et al, 1978;Leon et al, 1985). For Swiss mice, the behaviour at peak lactation was observed and classified into one of five categories: general activity, grooming, feeding, suckling and resting behaviour.…”

Section: Discussionmentioning

confidence: 88%

Effect of fur removal on the thermal conductance and energy budget in lactating Swiss mice

Zhao

Cao

2009

SUMMARYThe limits to sustained energy intake (SusEI) are important because they determine the ceiling restricting all the competing physiological processes. A recent hypothesis is that SusEI is constrained by the capacity to dissipate heat. However some previous data for Swiss mice are inconsistent with this hypothesis. To examine the role of limits to heat dissipation on SusEI, the body temperature, thermal conductance and lactation performance were measured in dorsally shaved Swiss mice. Shaving reduces external insulation and the heat dissipation limitation hypothesis predicts such animals should be capable of eating more food and raising heavier litters. Shaved mice had a significantly higher thermal conductance and a faster reduction in body temperature following noradrenaline injection. At peak lactation, shaved mice spent more time in feeding behaviour, and increased food intake above that observed in non-shaved controls, indicating that limits on SusEI might be imposed by the capacity to dissipate heat. However, shaved females did not spend more time suckling their pups, and did not raise heavier litters, which is inconsistent with the expectations of the heat dissipation limitation hypothesis. The strong correlations between resting, feeding and suckling behaviour at peak lactation suggested that there might be a trade-off in the time distribution between the behavioural patterns. These data suggest that limits on performance may be set at different levels in different strains or species. In MF1 mice studied previously the limit on milk production imposed by maximal mammary secretion capability may lie above that for heat dissipation, hence when the latter was increased the mice produced more milk and raised heavier litters. In Swiss mice the opposite might be the case. Hence when the heat dissipation capacity was increased this did not translate into heavier litters, i.e. supporting the peripheral limitation hypothesis. Further work in a range of additional species or strains will be necessary to establish whether the more normal condition is for SusEI in animals during late lactation to be set by combined peripheral demands or by the heat dissipation capacity.

“…In addition to this strongly supportive evidence for the HDL theory from large domesticated mammals, there is also a diverse literature on factors that affect maternal suckling behaviour in rodents. These data indicate that a key factor influencing maternal suckling duration is the risk of the mother overheating during the suckling bout (Leon et al, 1978;Leon et al, 1983;Bates et al, 1985;Leon et al, 1985;Adels and Leon, 1986;Newkirk et al, 1998). Further support for the HDL theory comes from comparisons of the reproductive performance of mice selectively bred to enhance their capacity to dissipate heat (Nielsen et al, 1997a;Nielsen et al, 1997b;Kgwatalala et al, 2004;McDonald and Nielsen, 2006).…”

Section: New Ideas On Limits To Sustained Energy Intakementioning

confidence: 97%

Limits to sustained energy intake. XIII. Recent progress and future perspectives

Speakman

Król

2011

Summary Several theories have been proposed to explain limits on the maximum rate at which animals can ingest and expend energy. These limits are likely to be intrinsic to the animal, and potentially include the capacity of the alimentary tract to assimilate energy – the ‘central limitation’ hypothesis. Experimental evidence from lactating mice exposed to different ambient temperatures allows us to reject this and similar ideas. Two alternative ideas have been proposed. The ‘peripheral limitation’ hypothesis suggests that the maximal sustained energy intake reflects the summed demands of individual tissues, which have their own intrinsic limitations on capacity. In contrast, the ‘heat dissipation limit’ (HDL) theory suggests that animals are constrained by the maximal capacity to dissipate body heat. Abundant evidence in domesticated livestock supports the HDL theory, but data from smaller mammals are less conclusive. Here, we develop a novel framework showing how the HDL and peripheral limitations are likely to be important in all animals, but to different extents. The HDL theory makes a number of predictions – in particular that there is no fixed limit on sustained energy expenditure as a multiple of basal metabolic rate, but rather that the maximum sustained scope is positively correlated with the capacity to dissipate heat.