Behavioral Abnormalities in Young Adult Pigs Caused by Malnutrition in Early Life

Abstract

Baby pigs were malnourished for a period of 8 weeks by restricting protein or calorie intake with the objective of studying behavioral changes that remained long after nutritional rehabilitation had been achieved. An apparatus was designed for the measurement of changes in the level of excitement or emotionality under conditions of stress, as well as changes in learning performance in a conditioned avoidance situation. The most striking behavioral change due to early malnutrition was the heightened excitement of the pigs when exposed to aversive stimuli, although there was also an indication of decreased learning ability. Since learning performance can be affected by behavioral factors that influence the level of reinforcement (reward or punishment), impaired learning may be due either to decreased intelligence (capacity) or to elevated excitement and consequent over-reaction to reinforcement. The nutritional condition which caused the greatest change in behavioral development resulted from feeding a diet very low in protein from the third through the eleventh week of life. Behavioral abnormalities were also noted, although in lesser degree, if the low protein diet was initiated later, i.e., seventh to fifteenth week of life or if a diet of normal composition was fed in restricted quantity so as to prevent growth during an 8-week period starting either at birth or at 3 weeks of age.