DIETARY ENERGY RESTRICTION-MEDIATED GROWTH AND MAMMARY DEVELOPMENT INRATS

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