Relationships Among Maternal Size and Carcass Composition, Lactational Performance, and Growth and Composition of the Young: Comparisons Across Varying Degrees of Chronic Malnutrition

Abstract

To describe the relationships among dietary intake, lactational performance, and litter growth in chronically underfed Sprague-Dawley rats, data from four studies were combined. In all experiments, animals were assigned at random to their dietary treatment group at 42 d of age and were bred over a 3- or 4-wk period beginning at 70 d of age. Throughout the experiments, rats were fed diet AIN-76A ad libitum (AL) or were fed 75%, 60%, 50% or 40% of AL intake. Litter size was adjusted to 8 pups at day 1 of lactation (L). At day 14 of L, milk yield was determined among half the dams by the tritiated water method. Milk and carcass composition were determined among the remaining dams and litters. At day O of L, maternal weight was a positive, linear function of food intake. At day 14 of L, milk yield and energy content were positively related to maternal body weight and carcass fat values; both increased at decreasing rates as body weight and carcass fat increased. Only within the AL range were decreases in maternal food intake not associated with compromised lactational performance. Pup weight gain also was compromised by restriction of maternal food intake but not by changes in maternal food intake within the AL range. At any given milk energy intake, pups of the AL-fed dams grew better than those of the restricted dams. Weight gain of the pups increased at a decreasing rate as a function of milk energy intake. The pups of restricted dams grew better as milk energy increased, whereas the pups of AL-fed dams grew at similar rates across a wide range of milk energy intake. A potential explanation for this is that as maternal food intake increased pups of the AL-fed dams deposited more of their new tissue as fat; however, the limited data available here on litter carcass composition are insufficient to support this hypothesis. This is the first time that these relationships have been explored across varying degrees of chronic underfeeding. These data support the existence of a non-linear relationship between chronic dietary intake and lactational performance. They also provide clear evidence of adaptation in milk yield and pup growth over the range of intake characteristic of AL-fed rats. However, this adaptation was overwhelmed by maternal dietary restriction with a resultant compromise in lactational performance and pup weight gain. (Supported by NIH Grant HD-14953.)