Bioavailability of calcium in sun-cured alfalfa meal and effect of dietary calcium concentration on bone and plasma characteristics during two phases of gestation in gilts.

A study was conducted with gravid gilts to determine the bioavailability of Ca in sun- cured alfalfa meal (AM) and the effect of dietary Ca concentration on bone and blood characteristics during two phases of gestation. Two Ca sources (AM and CaC03), three dietary concentrations of Ca (50, 75, and 100% of the NRC requirement), and two gestation phases (55 and 105 d) were used in a 2 x 3 x 2 factorial arrangement in a randomized design with five replications (60 gravid gilts). Response criteria were as follows: 1) plasma Ca, P, and alkaline phosphatase (AKP) measured at the onset and at 25-d intervals and 2 ) metacarpal (M C ) and metatar- sal (MT) bone breaking strength (kilograms), ash content (percentage), density (grams/cubic cen- timeter), and ash density (grams of ashicubic cen- timeter) at the conclusion of the experiment. Plasma Ca, P, and AKP concentrations were similar between Ca sources. Because the response between Ca sources was similar, the data were pooled among sources. There was a linear decline in plasma P and AKP (P I .05) as dietary Ca concentration increased. As gesta- tion progressed from 0 to 100 d, there was a decline (P < .05) in plasma Ca and P. There were no differences in bone breaking strength and ash between Ca sources in either the MC or MT. No differences in bone strength between gestation phases occurred. A gesta- tion phase x dietary Ca concentration interaction (P < .05) was observed for bone ash in both bones. An interaction (P I.07) between Ca source and diet Ca concentration occurred for bone and ash density in the MC. There were differences in plasma Ca, P, and AKP as gestation progressed. The Ca in the AM used in this experiment was found to be as bioavailable as the Ca in CaC03 when fed to gravid swine.