Eight groups of 13-15 female rats were fed purified diets after littering. Four groups received a low
protein (8%
casein) diet (groups 8) and the others, a normal
protein (20%
casein) diet (groups 20).
Carbohydrates were supplied either as
starch (groups S) or as
starch plus 40%
fructose (groups F). Half the animals received a 0.4%
methionine supplementation (groups M). Four or five dams per group were sacrificed on days 2, 7 and 14 after littering. The diet intake was increased by
methionine supplementation, substitution of
starch for
fructose and increased
protein content, mainly during the second week of lactation. This influenced weight variation of the dams and litter growth. On all days, the plasma levels of
cholesterol esters,
triglycerides and
phospholipids were positively correlated with the
dietary protein level. On days 7 and 14, the liver neutral
lipid content was increased in rats fed the
low protein diets supplemented with
methionine (groups 8SM and 8FM) and the normal
protein diets containing 40%
fructose (groups 20F and 20FM). The plasma free
threonine content was positively correlated with the
protein level in the diet. On day 14, rats fed a
low protein diet had a
threonine deficiency, except those in groups 8S and 8F. The plasma free
threonine content of these rats was not reduced, possibly due to an impaired utilization of this
amino acid. The liver
lipidosis observed during lactation, in contrast to that observed during growth with a
low protein diet, was not due to a
threonine deficiency.