This study was conducted to examine the effects of cimaterol feeding on growth performances and mammary growth and differentiation. Attempts were also made to investigate the cellular metabolisms of protein and fat in the mammary gland at the various physiological stages (virgin, pregnancy, early lactation, and late lactation). Ninety-six female Sprague Dawley rats (approximately 52.3 g) were randomly assigned to three treatments: CON (feeding the diet without cimaterol), CIM I (feeding the diet with cimaterol [10 mg/kg] from weanling to parturition), CIM II (feeding the diet with cimaterol from breeding to parturition). Cimaterol improved (P < 0.01) body weight gain and feed intake and reduced (P < 0.01) feed efficiency. In the mammary gland, DNA, RNA, and protein content were increased, and lipid content was decreased, by feeding cimaterol. Also, functional activity (RNA/DNA) and size (protein/DNA) of mammary gland cells were increased by cimaterol. It was clear that the lipogenic activity in the mammary gland was increased with lactogenesis, although cimaterol had no effect on lipogenic activity. But cimaterol was effective in increasing lipolytic activity. As a result of in vitro acinar mammary cell culture, cimaterol showed a direct effect on increasing protein synthetic activity (P < 0.01). It was observed through this study that cimaterol functions not only on energy repartitioning but also on growth and mammary development and differentiation in rats.
