Meeting Abstract

38.6  Friday, Jan. 4  Maternal investment depends on season in reproducing European hares VALENCAK , TG*; TATARUCH, F; RUF, T; University of Veterinary Medicine Vienna; University of Veterinary Medicine Vienna; University of Veterinary Medicine Vienna teresa.valencak@vu-wien.ac.at

Compared to other precocial mammals, European hares bear high lactational costs. These costs may be caused by the year-round exposition to harsh environmental conditions (since hares lack protective burrows), by the offspring�s need for fast growth and consequently, by the production of high caloric milk with a fat content exceeding 20%. We hypothesized that in hares, investment in offspring and resource allocation may differ in the course of the reproductive season. Therefore, we measured energy expenditure during lactation over the breeding season. Experimental females were paired three times between February and August, and successfully raised three (size-manipulated) litters with three pups each. We assessed energy budgets of females as well as milk quality and total milk transfer to young. We found that the in the course of the breeding season fat and energy content of milk decreased, while the amount of milk production significantly increased. Despite this compensatory increase, total energy transfer to young was significantly decreased in fall. This points to an important role of fat reserves which are solely built up in the preceding winter months in hares. Lactating females reached peak sustained metabolic rates in the autumn litters, when fat reserves were already depleted and assimilated energy was highest. Peak energy assimilation in autumn was related to the length of the gastrointestinal tract. We conclude that (i) in hares, maximum sustained energy turnover during lactation varies seasonally and is regulated according to the availability of body energy stores, and (ii) that hares shift from a ‘capital’ to an ‘income breeder’ strategy of resource allocation within the breeding season.