Humeral skeletal development and plasma constituent changes in fetuses of ewes maintained on a low calcium diet from 60 days of gestation |
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Authors: | M S Lima F Kallfelz L Krook P W Nathanielsz |
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Institution: | (1) Department of Pathology, College of Veterinary Medicine, Cornell University, 14853 Ithaca, New York, USA;(2) Department of Physiology, College of Veterinary Medicine, Cornell University, 14853 Ithaca, New York, USA;(3) Laboratory for Pregnancy and Newborn Research, College of Veterinary Medicine, Cornell University, 14853 Ithaca, New York, USA |
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Abstract: | Summary The objective of this study was to evaluate the effects of a long-term, low-calcium diet on fetal calcium metabolism and fetal
skeleton skeleton development in ewes. Eleven pregnant sheep were assigned to two groups, fed either a diet low in calcium
(0.26% total dry matter) or normal in calcium (0.8% total dry matter) for 2 months, starting at 60 days gestational age. The
ewes fed the low calcium diet showed lower plasma levels of calcium and higher plasma levels of hydroxyproline, parathyroid
hormone, and 1,25 (OH)2D compared with the ewes fed the normal calcium diet. There were no differences in these variables between the two groups
of fetuses. These observations suggest that the plasma components of calcium homeostasis measured in the fetal lamb in the
present study are independent of the ewe and are not significantly affected by the presence of lowere maternal calcium for
many weeks during pregnancy. Despite the ability of the fetus of the ewe on the low calcium diet to maintain relatively normal
circulating plasma components of calcium homeostasis, long-term maternal hypocalcemia delayed fetal skeletal ossification
as shown by histological examination of the fetal humerus. The fetal humerus from low calcium-fed ewes showed a lower proportion
of bone versus cartilage (45.6±5.9 versus 57.4±4.6%, mean ±SD) lower ash content (15.4±1.5 versus 17.4±1.0%), and lower specific
gravity (1.19±0.2 versus 1.22±0.02) (P<0.05) than the humerus from fetuses of normal calcium-fed ewes. This study shows that the long-term calcium intake of the
ewe does affect fetal skeletal development, despite a lack of observable effects on fetal plasma concentrations of calcium
or known calcium regulating hormones such as 1,25(OH)2D or parathyroid hormone. |
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Keywords: | Ovine fetuses Hypocalcemia Parathormone 1 25 Dihydroxyvitamin D |
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