Body temperature of huddling newborn Zucker rats.

Daily mean core temperature (Tc) in huddling Zucker rat pups reared at 25 degrees C revealed the onset of a significantly lower Tc in fa/fa pups on day 6. The difference between any pup's Tc and the mean Tc of that half of the litter with the highest Tc on any given day was an early marker for genotype. Calculating the mean difference for any 2 consecutive days from day 6 onwards gave values for each fa/fa pup that were outside the 99% confidence limits for the individual observations in the Fa/- pups.