Limits to sustained energy intake XXIV: impact of suckling behaviour on the body temperatures of lactating female mice.

Y Gamo,H Gray,A Bernard,C Hambly,N Jeannesson,S E Mitchell,J Miller,J Dixon,F Munro,A Campbell,J R Speakman,K Derrer,C Troup,L M Vaanholt

doi:10.1038/srep25665

Abstract

The objective of this study was to investigate the potential causes of high body temperature (Tb) during lactation in mice as a putative limit on energy intake. In particular we explored whether or not offspring contributed to heat retention in mothers while suckling. Tb and physical activity were monitored in 26 female MF1 mice using intraperitoneally implanted transmitters. In addition, maternal behaviour was scored each minute for 8 h d−1 throughout lactation. Mothers that raised larger litters tended to have higher Tb while nursing inside nests (P < 0.05), suggesting that nursing offspring may have influenced heat retention. However, Tb during nursing was not higher than that recorded during other behaviours. In addition, the highest Tb during the observation period was not measured during nursing behaviour. Finally, there was no indication that mothers discontinued suckling because of a progressive rise in their Tb while suckling. Tb throughout lactation was correlated with daily increases in energy intake. Chronic hyperthermia during lactation was not caused by increased heat retention due to surrounding offspring. Other factors, like metabolic heat produced as a by-product of milk production or energy intake may be more important factors. Heat dissipation limits are probably not a phenomenon restricted to lactation.

Highlights

Food intake at peak lactation in small mammals reaches an asymptote and appears to be limited[1]
Direct observations suggest that lactating MF1 mice are chronically hyperthermic compared to non-reproductive and pregnant individuals[17,18] and this is consistent with more sporadic body temperature (Tb) measurements reported in several other small rodents during lactation, such as Mongolian gerbils (Meriones unguiculatus)[19], Dwarf hamsters (Phodopus campbelli and P. sungorus)[20] and Sprague-Dawley rats (Rattus norvegicus)[21]
Prediction 1a: Tb will increase towards the end of nursing bouts? Tb during four nursing bouts selected randomly from a single female mouse show the diversity of patterns of maternal Tb over time when females were nursing (Supplementary Fig. 1)

Summary

Introduction

Food intake at peak lactation in small mammals reaches an asymptote and appears to be limited[1]. Direct observations suggest that lactating MF1 mice are chronically hyperthermic compared to non-reproductive and pregnant individuals[17,18] and this is consistent with more sporadic body temperature (Tb) measurements reported in several other small rodents during lactation, such as Mongolian gerbils (Meriones unguiculatus)[19], Dwarf hamsters (Phodopus campbelli and P. sungorus)[20] and Sprague-Dawley rats (Rattus norvegicus)[21]. These data suggest hyperthermia risk may be a broadly applicable limitation on lactation performance. Heavier pups later in lactation might result in more maternal hyperthermia than smaller pups earlier in lactation because the body surface in contact with pups would be greater and these pups would be hotter because they are themselves thermo-competent later in lactation (Prediction 3)

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Results

Discussion

Conclusion