EFFECT OF OVARIECTOMY ON BONE-HISTOLOGY AND PLASMA PARAMETERS OF BONEMETABOLISM IN NULLIPAROUS AND MULTIPAROUS SOWS

To investigate the suitability of the pig as animal model for postmeno pausal osteoporosis, effects of ovariectomy (OVX) on bone metabolism a nd histology were studied in two groups of sows (9 months, nulliparous or 35 months, multiparous). A standard diet of about 1.5 % calcium (C a) was fed till sacrifice at either 12 or 20 months post OVX when mine ral content and histology were studied in representative bone specimen s of proximal tibia, iliac crest and lumbar vertebrae. At 4, 8, 12, an d 18 months post OVX, total and bone-specific alkaline phosphatase (AP (t), AP(b)) calcidiol, calcitriol and parathyroid hormone (PTH) were m easured in plasma. In young sows OVX did not significantly affect plas ma variables except for calcitriol, which was higher at 4 months post OVX. No significant differences between OVX or control animals were ob served in the variables of bone chemical and histological analyses, ne ither 12 nor 20 months post OVX. In multiparous sows OVX significantly increased PTH plasma concentrations at 8 months post OVX and plasma c alcitriol, AP(t) and AP(b) at 12 months post OVX. All effects were mod erate and transient. OVX did not significantly affect the variables of bone chemical and histological analyses neither 12 nor 20 months post OVX. Although undoubtedly the clinical-chemical changes observed were not accompanied by any histomorphometric signs of osteopenia/osteopor osis, it must be left to future experiments as to whether this resulte d from the ample calcium supply provided. This possibility is supporte d by recent observations showing that porcine osteopenia could be indu ced by OVX in animals maintained on only 0.75 % dietary calcium but no t on higher (0.9 %) Ca regimens (33).