Dietary energy restriction-mediated growth and mammary development in rats

This research examined the extent to which dietary energy restriction modulates growth and mammary tissue composition during different developmental stages. Female rats were assigned to the following three dietary treatments: 1) ad libitum access to feed (AL), 2) 30% continuous energy restriction (CER), and 3) stair-step energy restriction (SSER). The SSER treatment consisted of an 8-wk, alternating schedule beginning with 60% energy restriction for 2 wk, followed by realimentation to feed offered for ad libitum intake for 2 wk. All treatments were initiated when rats were 5 wk of age. After the stair-step regimen, SSER rats were maintained on a 30% energy-restricted diet for the duration of the experimental period (25 wk of age). Rats reared on the energy restriction regimens weighed less and consumed less (P < .05) feed than controls, but they had feed efficiencies similar to those of controls. Energy restriction delayed the onset of puberty and retarded the growth of the offspring but had no effect on litter size. The overall values (averaged pregnancy through involution stages) of DNA, RNA, and RNA: DNA ratio (based on fat-free DM) and protein concentrations were similar in the mammary tissues of the energy restriction groups and those of the AL group. Lipid content in mammary tissue was generally decreased in the CER and SSER groups compared with the AL group. In summary, energy restriction delayed the onset of puberty and retarded the growth of the dam and progeny, but it did not affect mammary cellularity as it reduced fat deposition in the mammary gland.