EFFECT OF CALCIUM SOURCE, DIETARY CALCIUM-CONCENTRATION, AND GESTATION PHASE ON VARIOUS BONE CHARACTERISTICS IN GESTATING GILTS

Sixty gravid crossbred gilts were allotted to a 2 x 3 x 2 factorial ar rangement of treatments: two Ca sources (sun-cured alfalfa meal and Ca CO3), three dietary concentrations of Ca (50, 75, and 100% of NRC requ irements), and two phases of gestation (55 and 105 d). The objectives were to determine the effect of Ca source, dietary Ca concentration, a nd gestation phase on bone characteristics (bone breaking strength, bo ne ash percentage, bone density, and bone ash density in the rib, thor acic, and coccygeal bones), to correlate bone responses to determine r elative bone activity, and to determine reliability of the coccygeal b ones as indicators of Ca status in the body. At 55 d, rib strength and coccygeal ash content were lower (P < .01) than at 105 d of gestation . A gestation phase x Ca concentration (P < .05) interaction occurred. As Ca concentration increased, thoracic strength and rib ash responde d quadratically during each gestation phase, for which at 55 d a minim a and at 105 d a maxima was produced at 75% of NRC. A Ca source x Ca c oncentration (P < .05) interaction occurred. Gilts fed alfalfa had the lowest rib bone and ash density when fed 75% of NRC for Ca, whereas g ilts fed CaCO3 were highest at this level of Ca compared with the othe r concentrations. Generally, all bones were positively correlated with respect to their response to dietary Ca concentration. Few negative c orrelations were observed. At this level of physiological maturity, th ere was no effect of Ca source and little effect of gestation phase on the bone variables measured at the dietary Ca concentrations used in this experiment. The rib and thoracic bones seem to be the most respon sive to dietary Ca concentration.