ENVIRONMENTAL-TEMPERATURE AND METABOLIC RATES DURING GESTATION AND LACTATION IN GOLDEN-HAMSTERS (MESOCRICETUS-AURATUS)

We determined the influence of ambient temperature (T-a) on energetic costs of reproduction by measuring resting metabolic rate (RMR); body temperature (T-b) measured rectally, and respiratory quotient (RQ) at six reproductive stages (premating, middle and late gestation, early, middle, and late lactation) of reproductively active (RA) golden hamsters maintained at 24 degrees C (RA-24) and 30 degrees C (RA-30), with nonreproductive (NR) females as controls. Reproductively active and NR hamsters consumed more O-2 at 24 degrees C than at 30 degrees C (within the zone of thermoneutrality), but only NR females had a lower RQ at the lower T-a. Gestation caused significant (P < 0.05) increase in the adjusted RMR of RA-30 dams (as compared to the RMR of the NR-30 controls), but this effect of gestation was not detected in RA-24 darns. Lactating hamsters had higher RMR than did NR females at both T-a's. In addition, RA-30 darns had lower RQ during gestation and higher T-b during lactation. These results indicate that increased metabolic costs of gestation are undetectable in golden hamsters maintained below thermoneutrality and that RMR is highest midway through the period of lactation in females maintained at both 24 degrees C and 30 degrees C.