Energy turnover in European hares is centrally limited during early,but not during peak lactation |
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Authors: | Teresa G Valencak Thomas Ruf |
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Institution: | (1) Research Institute of Wildlife Ecology, University of Veterinary Medicine, Savoyenstrasse 1, 1160 Vienna, Austria; |
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Abstract: | We investigated metabolizable energy intake (MEI) and milk energy output in European hares throughout gestation and lactation
in females raising three young, i.e., close to maximum litter size in this precocial species. We hypothesized that herbivorous
hares may face a central limitation of energy turnover during lactation, imposed by maximum capacity of the gastrointestinal
tract. Females were provided with low-energy or high-energy diets, either continually, or during lactation only. Unexpectedly,
females on either diet reached identical peak MEIs (>6 times BMR) during late lactation, with females on low-energy diet increasing
food intake proportionally. Thus, we reject our hypothesis that in lactating hares, peak MEI is centrally limited. During
early lactation, MEI and milk transfer was, however, significantly impaired in females on the low-energy diet, indicating
a temporal central limitation due to a time-lag caused by the readjustment of energy intake capacity. Importantly, irrespective
of the diet, females significantly increased peak MEI late in the breeding season. Consequently, earlier in the season, when
energy reserves are still high, energy throughput was not limited by physiological constraints at all. We conclude that extreme
MEI may have fitness costs, and that females maximize lifetime reproductive success by actively down-regulating MEI whenever
possible. |
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