Short communication: Proteins in heat-processed skim milk powder have no positive effects on bone loss of ovariectomized rats

Milk has positive effects on bone growth. However, the effect of skim milk powder (SMP) on bone properties has not been reported. This study investigated the effect of SMP on bone loss in ovariectomized (OVX) rats. Forty female Sprague-Dawley rats were ovariectomized and another 10 rats received a sham operation. The OVX rats were randomly separated into 4 groups: OVX control, OVX SMP1 (SMP at 0.04 g/d), OVX SMP2 (SMP at 0.20 g/d), and OVX SMP3 (SMP at 0.40 g/d). Skim milk powder was supplied in the rat diet for 12 wk, and the rats were gavaged once per day. The effects of SMP on calcium content and bone mineral density of femur were determined by atomic absorption spectrophotometry and dual-energy x-ray absorptiometry, respectively. Compared with the control, SMP at all dose levels tested had no particular effect on weight:length, calcium content, or bone mineral density of femurs. It was demonstrated that SMP (0.04 to 0.40 g/d) had no positive effect on bone loss in OVX rats, probably because the heat treatment used during SMP processing caused a loss of biological activity in the protein.