title: Limits to sustained energy intake XXV: milk energy output and thermogenesis in Swiss mice lactating at thermoneutrality.
abstract: Previous studies at 21 °C and 5 °C suggest that in Swiss mice sustained energy intake (SusEI) and reproductive performance are constrained by the mammary capacity to produce milk. We aimed to establish if this constraint also applied at higher ambient temperature (30 °C). Female Swiss mice lactating at 30 °C had lower asymptotic food intake and weaned lighter litters than those at 21 °C. Resting metabolic rate, daily energy expenditure, milk energy output and suckling time were all lower at 30 °C. In a second experiment we gave mice at 30 °C either 6 or 9 pups to raise. Female performance was independent of litter size, indicating that it is probably not controlled by pup demands. In a third experiment we exposed only the mother, or only the offspring to the elevated temperature. In this case the performance of the mother was only reduced when she was exposed, and not when her pups were exposed, showing that the high temperature directly constrains female performance. These data suggest that at 30 °C SusEI and reproductive performance are likely constrained by the capacity of females to dissipate body heat, and not indirectly via pup demands. Constraints seem to change with ambient temperature in this strain of mouse.
authors.affiliation: School of Life and Environmental Sciences, Wenzhou University, Wenzhou, Zhejiang 325027, China.
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100100, China.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100100, China.|State Key Laboratory of Integrated Management for Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: Deng-Bao
authors.initials: DB
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Integrated Management for Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China.
authors.forename: Qing-Sheng
authors.initials: QS
authors.lastname: Chi
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Scotland, UK.
authors.forename: Catherine
authors.initials: C
authors.lastname: Hambly
authors.affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100100, China.|Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Scotland, UK.
authors.forename: John R
authors.initials: JR
authors.lastname: Speakman
mesh_terms: D000818:Animals; D001481:Basal Metabolism; D001823:Body Composition; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D007774:Lactation / Q000502:physiology*; D008098:Litter Size; D008297:Male; D051379:Mice; D022722:Thermogenesis