Late lactation in small mammals is a critically sensitive window of vulnerability to elevated ambient temperature

Zhi-Jun Zhao* (Corresponding Author), Catherine Hambly, Lu-Lu Shi, Zhong-Qiang Bi, Jing Cao, John R Speakman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Citations (Scopus)


Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (Cricetulus barabensis), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.

Original languageEnglish
Pages (from-to)24352-24358
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number39
Early online date14 Sept 2020
Publication statusPublished - 29 Sept 2020

Bibliographical note

This work was partly supported by grants (31670417, 31870388) from the National Natural Science Foundation of China and the Chinese Academy of Sciences Strategic Program (XDB13030100). We thank Song Tan and Jing Wen from Wenzhou University for their assistance with animal care, and Peter Thomson and Marina Stamatiou from the University of Aberdeen for technical assistance with isotope analysis.

All relevant data have be placed on the Open Science framework (identifier: DOI 10.17605/OSF.IO/WBNG9).


  • lactation
  • energetics
  • climate change
  • lethal temperature
  • heat waves


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