engleski

Costs of concurrent pregnancy and lactation in highly precocial guinea pigs (Cavia aperea f. porcellus and Cavia aperea) and highly altricial mice (Mus musculus)

For mammals, lactation represents the most energetically demanding time. Many rodents with a postpartum oestrus can be concurrently lactating and pregnant. In such a state energetic demands may be even higher due to the additional energetic demands of pregnancy. During lactation when costs for female mammals are highest, metabolic savings can be achieved by minimizing activity levels. In contrast to many small altricial mammals where lactation lasts about as long as lactation and the two phases may completely overlap in concurrently pregnant and lactating females, in small precocial mammals gestation is much longer than lactation and patterns of energetic demands of lactation and pregnancy are also different in precocial mammals. Effects of concurrent pregnancy and lactation may therefore differ between altricial and precocial species. I therefore used the highly precocial guinea pig and highly altricial species, the laboratory mouse for comparison in this study. 1. In the first part of the study I compared concurrently pregnant and lactating domestic guinea pig (Cavia aperea f. porcellus) females and their litters with lactating only females and their litters regarding food intake and RMR as well as body mass during the whole period of lactation. No evidence of differences in energetic demands between females of both treatments could be found. Further results demonstrated no significant difference in pup mass, litter mass or litter size during the whole lactation period. 2. In the second part I compared concurrently pregnant wild guinea pig (Cavia aperea) females with lactating only wild guinea pig females and their litters regarding RMR, body mass and also female activity. No difference was found between females of both treatments for all measured parameters. Activity of both treatments was lower on day 3 then on day 7 of lactation. 3. In the third part I compared the daily running activity of concurrently lactating and pregnant mice (Mus musculus) with lactating only and with pregnant mice. During pregnancy activity was higher than in both lactating groups. No difference was found in running activity between lactating - pregnant and lactating only females. During the whole reproductive cycle wheel running activity continuously decreased from 7.12 km/day in non-reproductive females to 0.53 km/day during last 3 days of gestation reaching its minimum of 0.19 km/day during late lactation. At day 16 of lactation the wheel running activity made only 0.02% of the total assimilated daily energy. This data shows that maternal investment as well as pup development seem not to be influenced by concurrent pregnancy and lactation in the highly precocial guinea pig. The activity of concurrently pregnant and lactating wild guinea pigs and mice was not different in comparison to activity of lactating only females. It can thus be concluded that females cope with this situation in a yet unknown way.

pregnancy; lactation; energetic cost of reproduction; postpartum oestrus; concurrent pregnancy and lactation; running activity

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