Meeting Abstract

P3.17  Thursday, Jan. 6  Lactating hares in the cold: the role of heat dissipation VALENCAK, TG*; RUF, T; University of Veterinary Medicine Vienna; University of Veterinary Medicine Vienna Teresa.Valencak@vetmeduni.ac.at

Similar to small rodents, European hares (Lepus europaeus), reach extremely high levels of energy turnover during lactation. In hares, energy turnover levels off during late lactation, and does not increase at litter sizes beyond 2 young, indicating an upper limit to lactational performance. Previously, it has been suggested that maximum sustained metabolic rates (SusMR) are due to physiological constrains, such as central limitation by the gastrointestinal tract or peripheral limitations, such as the capacity of mammary gland. More recently it has been shown in laboratory mice that the maximum rate of heat dissipation of lactating females can be limiting for SusMR. Here, we experimentally tested whether heat dissipation rates may also constrain energy turnover in lactating European hares. For this purpose, we made use of the fact that hares nurse their young only once per day, which allowed us to keep females and young either at the same or different ambient temperatures. Females were able to significantly increase metabolisable energy intake (MEI) and milk energy output (MEO) in response to increased energy requirements of cold exposed (5° C) young, irrespective of whether the mothers were kept at thermoneutrality (22 °C) or also cold exposed (5 °C). Further, mothers of cold-exposed young reached significantly higher rates of both MEI and MEO than those with leverets at thermoneutrality, indicating that apparent peak rates of energy turnover in the latter group (mothers and young at 22 °C) were limited neither centrally nor peripherally. We suggest that operating at SusMR might have considerable physiological costs for females, which may pay off only if the reproductive value of the offspring is particularly high.