Limits to sustained energy intake XIX: A test of the heat dissipation limitation hypothesis in Mongolian gerbils (Meriones unguiculatus)

Abstract

SUMMARY We evaluated factors limiting lactating Mongolian gerbils (Meriones unguiculatus) at three temperatures (10, 21 and 30°C−1 less energy as milk at peak lactation than those allocated to 10 or 21°C, with no difference between the latter groups. On day 14 of lactation, the litter masses at 10 and 30°C were 12.2 and 9.3g lower than those at 21°C, respectively. Lactating gerbils had higher thermal conductance of the fur and lower UCP-1 levels in brown adipose tissue than non-reproductive gerbils, independent of ambient temperature, suggesting that they were attempting to avoid heat stress. Thermal conductance of the fur was positively related to circulating prolactin levels. We implanted non-reproductive gerbils with mini-osmotic pumps that delivered either prolactin or saline. Prolactin did not influence thermal conductance of the fur, but did reduce physical activity and UCP-1 levels in brown adipose tissue. Transferring lactating gerbils from warm to hot conditions resulted in reduced milk production, consistent with the heat dissipation limit theory, but transferring them from warm to cold conditions did not elevate milk production, consistent with the peripheral limitation hypothesis, and placed constraints on pup growth. Supplementary material available online at

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

“…The Journal of Experimental Biology (2014) (Yang et al, 2013). Consistent with the prediction of the HDL theory, the peak metabolisable energy intake in lactation (days 13-15) was significantly higher in the MH line compared with the ML line.…”

“…In MF1 mice, observations of milk production and pup growth at the different temperatures [enhanced in the cold and reduced in the heat (Johnson and Speakman, 2001;Król and Speakman, 2003b)] strongly supported only the HDL idea. Yet in other studies, cold exposure did not have an impact on pup growth (Zhang and Wang, 2007;Zhao and Cao, 2009;Zhao et al, 2010;Zhao et al, 2013b;Yang et al, 2013), supporting the other two ideas.…”

“…During lactation food intake increases enormously (Johnson et al, 2001a) and conspicuously reaches a plateau in late lactation that is resistant to attempts to breach it by imposing additional workloads on the female, for example, by manipulating litter size or pup demands (Hammond and Diamond, 1992;Johnson et al, 2001a;Laurien-Kehnen and Trillmich, 2003;Duah et al, 2013), by making females simultaneously pregnant (Johnson et al, 2001c), or by forcing them to run to obtain their food (Perrigo, 1987;Zhao et al, 2013a). However, when lactating animals are placed in the cold, they are able to eat significantly more than at room temperature Hammond and Kristan, 2000;Johnson and Speakman, 2001;Rogowitz, 1998;Zhang and Wang, 2007), and conversely when kept in hot conditions their maximal intake declines (Król and Speakman, 2003a;Wu et al, 2009;Yang et al, 2013). This effect could be explained either by the HDL theory, the summed peripheral demands idea or temperature-dependent variations in pup energy demands.…”

“…Moreover, multiple constraints may apply in the same individuals under different conditions, for example, at different ambient temperatures (Yang et al, 2013) or at different litter sizes (Wu et al, 2009). More experimental data across a range of different animal models are needed to enhance our understanding of the factors that are of potential importance in limiting SusEI.…”

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

“…Consistent with this idea, dorsally shaved MF1 mice had increased thermal conductivity, and were thus able to produce more milk and wean heavier litters (Król et al, 2007). Studies on Brandt's voles (Wu et al, 2009) and Mongolian gerbils (Yang et al, 2013) both revealed that high temperatures (30°C) induced a reduction in milk production. Although these data supported the HDL theory, the effect in voles was greatest in females raising the largest litters, and in small litters there was no significant effect of high temperature (Wu et al, 2009).…”