title: Limits to sustained energy intake. XXI. Effect of exposing the mother, but not her pups, to a cold environment during lactation in mice.
abstract: The capacity of females to dissipate heat may constrain sustained energy intake during lactation. However, some previous experiments supporting this concept have confounded the impact of temperature on the mothers with the impact on the pups. We aimed to separate these effects in lactating laboratory mice (MF1 strain) by giving the mothers access to cages at two ambient temperatures (10 and 21°C) joined by a tube. Food was available only in the cold cage, but females could also choose go to this cage to cool down while their pups were housed in the warmer cage. Control animals had access to the same configuration of cages but with both maintained at 21°C. We hypothesised that if females were limited by heat dissipation, alleviating the heat load by providing a cool environment would allow them to dissipate more heat, take in more food, generate more milk and hence wean heavier litters. We measured maternal energy budgets and monitored time courses of core body temperature and physical activity. To minimise the variance in energy budgets, all litters were adjusted to 12 (±1) pups. Females in the experimental group had higher energy intake (F1,14=15.8, P=0.0014) and higher assimilated energy (F1,13=10.7, P=0.006), and provided their pups with more milk (F1,13=6.65, P=0.03), consistent with the heat dissipation limit theory. Yet, despite keeping demand constant, mean pup growth rates were similar (F1,13=0.06, P=0.8); thus, our data emphasise the difficulties of inferring milk production indirectly from pup growth.
authors.affiliation: Institute of Genetics and Developmental Biology, State Key Laboratory of Molecular Developmental Biology, Chinese Academy of Sciences, Beichen Xi Lu, Chaoyang, 100101 Beijing, People's Republic of China.
authors.forename: Teresa G
authors.initials: TG
authors.lastname: Valencak
authors.forename: Paul
authors.initials: P
authors.lastname: Wright
authors.forename: Ashleigh
authors.initials: A
authors.lastname: Weir
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Mitchell
authors.forename: Lobke M
authors.initials: LM
authors.lastname: Vaanholt
authors.forename: Catherine
authors.initials: C
authors.lastname: Hambly
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Król
authors.forename: John R
authors.initials: JR
authors.lastname: Speakman
mesh_terms: D000818:Animals; D000833:Animals, Suckling / Q000378:metabolism; D003080:Cold Temperature; D002149:Energy Intake; D005260:Female; D007774:Lactation; D018811:Maternal Exposure; D051379:Mice; D009043:Motor Activity
keywords: MF1; activity; body temperature; choice; heat dissipation limitation; physiological limitation; thermal conditions