Ethological analysis of mother-pup interactions and other behavioral reactions in rats: effects of malnutrition and tactile stimulation of the pups

Mother-pup interaction, as well as other behavioral reactions were studied during the lactation period in 24 litters of Wistar rats and their dams fed either a 16% (control - C; 12 litters) or a 6% (malnourished - M; 12 litte rs) protein diet, The diets were isocaloric, Throughout lactation there was a 36.4% weight loss of M darns and a 63% body weight deficit in the M pups when compared to control pups, During this period, half of the litters wer e exposed daily to additional tactile stimulation (CS or MS), while the oth er half were submitted to normal rearing conditions (CN or MN). The tactile stimulation of pups (handling) consisted of holding the animal in one hand and gently touching the dorsal part of the animal's body with the fingers for 3 min, A special camera and a time-lapse video were used to record litt er behavior in their home cages. Starting at 6 p.m. and ending at 6 a.m., o n days 3, 6, 12, 15, 18 and 21 of lactation, photos were taken at 4-s inter vals. An increase in the frequency (154.88 +/- 16.19) and duration (455.86 +/- 18.05 min) of suckling was observed throughout the lactation period in all groups compared to birth day (frequency 24.88 +/- 2.37 and duration 376 .76 +/- 21.01 min), but the frequency was higher in the C (84.96 +/- 8.52) than in the M group (43.13 +/- 4.37); however, the M group (470.2 +/- 11.87 min) spent more time suckling as compared with the C group (393.67 +/- 13. 09 min). The M darns showed a decreased frequency of resting position throu ghout the lactation period (6.5 +/- 2.48) compared to birth day (25.42 +/- 7.74). Pups from the C group were more frequently observed separated (73.02 +/- 4.38) and interacting (258.99 +/- 20.61) more with their mothers than the M pups (separated 66.94 +/- 5.5 and interacting 165.72 +/- 12.05). Tact ile stimulation did not interact with diet condition, showing that the kind of stimulation used in the present study did not lead to recovery from the changes induced by protein malnutrition. The changes in mother-pup interac tion produced by protein malnutrition of both may represent retardation in neuromotor development and a higher dependence of the pups on their mothers . These changes may represent an important means of energy saving and heat maintenance in malnourished pups.