Delayed Responses in Rats and Mice to Early Postnatal Diets

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Abstract
This is a study of the effect of the nature of diet lipids during early development on lipid metabolism and body weight in adult rats and mice. Female Sprague-Dawley rats were taken from their dams at 14 days of age and given milk replacer formulas containing either butterfat or soybean oil-coconut oil. Between 21 and 95 days of age the respective groups were fed purified diets with either 15% lard, 5% butterfat and 0.5% cholesterol or a 17% soybean oil-3% coconut oil mixture. From 95 days to 11 months of age both groups were fed the animal fat diet. Two groups of rats weaned at 21 days of age were the controls, being fed the same diets as the test animals after 21 days of age. Although all the rats were of normal size when 95 days old, the prematurely weaned rats fed animal or vegetable fat weighed 453 and 471 g, respectively, at 11 months of age and the respective normal controls, 381 and 357 g. The serum cholesterol of the prematurely weaned, animal fat-fed group was 142 mg/dl and the other three groups 109, 110 and 116 mg/dl. The mortality rate was highest in the prematurely weaned animal fat diet rats being 9/16 and lowest in the normally suckled vegetable oil diet group, 2/13. Male C57BL/6Schf mice were normally suckled on high or low linoleate milk until they were 30 days old. Despite intervening dietary treatment which inhibited hepatic lipogenesis, the response of fatty acid synthase to a low polyunsaturated fat diet from 60 to 81 days of age was significantly greater in mice that had consumed the low linoleate rat milk compared to mice suckled on high linoleate milk, 57.7 and 36.0 nmoles malonyl CoA incorporated/minute/mg protein respectively. Stock-fed mice which had been suckled on high linoleate milk were heavier at 8 months of age than their counterparts fed low linoleate rat milk, 43.0 and 33.6 g, respectively, and had higher activities of hepatic FAS, 17.6 and 5.4 nmoles malonyl CoA incorporated/minute/mg protein. There was no observed difference between the two groups of mice at 4.5 months of age.

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