A critical appraisal of two common "neonatal" experiment subjects.

A comparative study of 11 physiologic variables in 200 piglets and puppies during the first 7 days of life was done. Seven of 11 physiologic variables significantly changed in the 1st wk of the piglets' life. Five of 11 variables significantly changed in the first week of the puppies' life. Six of 11 variables were significantly different when the newborn piglet was compared to the newborn puppy. The rate and/or direction of 7 of 11 physiologic changes during the first day of life were significantly different when the piglet was compared to the puppy. It was concluded that there are marked physiologic differences between: the newborn piglets and the 7 day old piglet; the newborn puppy and the 7 day old puppy; the newborn piglet and the newborn puppy and the "maturation" rate of the piglet and the puppy.