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First published online October 16, 2009
Journal of Experimental Biology 212, 3455-3465 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.030338

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Limits to sustained energy intake. XI. A test of the heat dissipation limitation hypothesis in lactating Brandt's voles (Lasiopodomys brandtii)

Su-Hui Wu^1,2, Li-Na Zhang³, John R. Speakman³ and De-Hua Wang^1,*

¹ State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Datun Lu, Chaoyang, Beijing 100101, China
² Graduate School of the Chinese Academy of Sciences, Yuquan Lu, Beijing 100049, China
³ Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK

^* Author for correspondence (wangdh{at}ioz.ac.cn)

Accepted 7 May 2009

The maximum rate of sustained energy intake (SusEI) may limit reproductive effort, thermoregulatory capability and other aspects of an animal's energy expenditure. Consequently, factors that limit SusEI are of interest. The `heat dissipation limitation hypothesis' suggests that maximum SusEI during lactation is limited by the capacity to dissipate body heat generated as a by-product of processing food and producing milk. In the present study, we tested the heat dissipation limitation hypothesis in lactating Brandt's voles (Lasiopodomys brandtii). Female voles were mated and pregnant at 21(±1)°C. A random sample of animals was transferred into a hot room 30(±1)°C on the day of parturition. The energy intake of lactating voles at 30°C was always lower than that at 21°C. At peak lactation food intake was 3.3 g day^–1 lower at 30°C than at 21°C. There was no significant difference in digestibility. With similar mean litter sizes (7.26±0.46 pups at 21°C and 7.78±0.39 pups at 30°C at the beginning of parturition, 6.83±0.51 pups at 21°C and 7.73±0.50 pups at 30°C at weaning), the milk energy output of mothers, evaluated from the difference between metabolizable energy intake and daily energy expenditure measured by doubly labelled water, at 30°C was 23.3 kJ day^–1 lower than that at 21°C on days 14–16 of lactation. As for reproductive performance, there was a difference in the response to the higher temperature between mothers raising large and those raising small litters. For small litters (<7) there was no significant change in litter mass, but for large litters (<7) there was a significant decrease at the higher temperature. On average, in larger litters the pups were 15.5 g heavier on day 12 of lactation when raised at 21°C. Our data from Brandt's voles support the suggestion that SusEI at peak lactation is limited by heat dissipation capacity, particularly for those voles raising large litters. In smaller litters the peripheral limitation hypothesis may be more relevant. The importance of heat dissipation limits in species raising exclusively small litters needs to be investigated.

Key words: Brandt's voles (Lasiopodomys brandtii), lactation, heat dissipation limitation hypothesis, food intake, digestive efficiency, metabolizable energy intake, daily energy expenditure, milk energy output, pup energy content, doubly labelled water

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