Expression of kyphosis in young pigs is induced by a reduction of supplemental vitamin D in maternal diets and vitamin D, Ca, and P concentrations in nursery diets.

Kyphosis is an idiopathic disease characterized by abnormal, outward spinal curvature. A spontaneous outbreak and subsidence of kyphosis over a 4-mo period in the University of Wisconsin Swine Research and Teaching Center herd coincided with an accidental omission of vitamin D(3) in 1 of 2 premixes used in sow diets. This controlled experiment was conducted to determine whether vitamin D deletion from premixes used in sow diets would induce kyphosis in their offspring. Crossbred (Landrace × Large White), multiparous sows (n = 8) were fed corn-soybean meal diets supplemented with either 325 IU vitamin D(3)/kg (+D) or 45 IU vitamin D(3)/kg (-D) diet from breeding through lactation. The vitamin D concentrations duplicated formulations of diets fed during the earlier spontaneous outbreak. At weaning (approximately 4 wk), pigs were fed diets devoid of supplemental vitamin D and formulated to supply either 120% of the Ca and P requirements (HCaP) or 80% of the Ca and P requirements (LCaP) until wk 9. At wk 9, all pigs were fed the HCaP diet until wk 13. No evidence of kyphosis was observed in pigs at weaning. Pigs produced by -D sows and fed LCaP diets exhibited a 17% incidence (4/23 pigs) of kyphosis at wk 9. At wk 13, the incidence of kyphosis had increased to 32% (6/19 pigs). Unexpectedly at wk 13, pigs produced by +D sows and fed LCaP diets exhibited a 26% incidence (5/19 pigs) of kyphosis. None of the pigs fed HCaP diets from wk 4 to 13 displayed kyphosis, regardless of maternal diets. Evidence of kyphosis was detected at a younger age if pigs were produced by sows fed -D diets. Whole body and femur bone mineral content determined with dual energy X-ray absorptiometry were reduced (P < 0.05) in pigs fed LCaP vs. HCaP diets, but pigs produced by -D sows were more severely affected. Femur bending moments were reduced (P < 0.05) at wk 9 and 13 in pigs fed LCaP vs. HCaP diets. At wk 13, pigs produced by -D sows and fed LCaP diets had reduced (P < 0.05) bone mineral density and femur yield bending moment compared with pigs from +D sows fed LCaP diets. In conclusion, the 20 to 30% incidence of kyphosis induced by altering vitamin D, Ca, and P concentrations in maternal and nursery diets mimics the incidence observed in spontaneous outbreaks in afflicted herds. A reproducible vitamin D-induced kyphosis in young pigs offers a suitable model to study skeletal tissue characteristics, fetal skeletal tissue development, and potential treatments for pigs and human patients afflicted by this disease.

Triennial Growth Symposium: a novel pathway for vitamin D-mediated phosphate homeostasis: implications for skeleton growth and mineralization.

Systemic factors that ultimately affect skeletal growth involve interrelationships among Ca, parathyroid hormone (PTH), and conversion of 25-OH vitamin D(3) to the active hormone, 1α,25-(OH)(2)D(3). These interrelationships, with a focus on mechanisms that affect Ca homeostasis, are referred to as the Ca, PTH, and vitamin D axis. Relatively little research has focused on these interrelationships and P homeostasis. In the past decade, discovery of a previously unrecognized hormone involved in a pathway for P homeostasis offers opportunities to improve P efficiency without compromising skeletal growth and animal well-being. The objective of this review was to summarize pivotal research discoveries that led to the current understanding of the roles of fibroblast growth factor 23 (FGF23) in P homeostasis that are independent from the well-described pathways involved with Ca homeostasis. The novel pathways are referred to as the FGF23, P, and vitamin D axis. The peptide, FGF23, directly affects P homeostasis via action on renal target tissues to regulate Na-P transport proteins and renal 25(OH)D(3)-1α hydroxylase activity. Identification of bone as the primary site for FGF23 production ascribes an endocrine gland function to bone. Within 9 h after a single injection of recombinant FGF23, mice displayed hypophosphatemia and urinary P wasting. In contrast, FGF23 knockout mice displayed hyperphosphatemia and renal P conservation. These responses were independent of PTH. Applications of the FGF23, P, and vitamin D axis in dietary strategies for animal agriculture need to be explored. Development of dietary inputs to balance both Ca and P homeostasis are needed to improve skeletal growth and nutrient efficiency.