The effect of over-feeding newborn rabbits on somatic and visceral growth, body composition and long-term growth potential.

Newborn rabbits were over-fed by encouraging them to suck from two lactating does. These double-fed animals were compared with single-fed litter-mate controls. Single- and double-fed rabbits were compared with respect to body-weight, bone length and weights of heart, kidney, lung, liver, spleen, stomach, brain and adipose lobes at ages 7, 14 and 21 d and at 25 weeks. Body composition with respect to fat, protein and water was also analysed in animals killed during the first month of life. Double feeding had a profound effect on body-weight, such that by 21 d of age these animals weighed 65% more than controls. Longitudinal growth was also increased, but to a lesser extent. Organ weights were largely determined by body-weight with the exception of the brain which was unaffected by double feeding and the heart and adipose lobes which were represented to excess. Body composition studies demonstrated a marked increase in body fat and a decrease in body water as a percentage of body-weight in the double-fed. When mature, double-fed rabbits weighed a little more than controls and had accumulated significantly more fat. No other difference between them was demonstrated. Other experiments on rats, mice and pigs, along with these experiments on rabbits, suggest that young mammals respond to over-feeding with a limited increase in real growth associated with excess deposition of adipose tissue. Studies on infants of diabetic mothers have demonstrated that the human fetus responds to over-nutrition in a very similar way. Therefore we should be cautious about over-feeding human infants, especially premature ones, as it seems unlikely that excessive deposition of fat will be beneficial.