260 The Effect of Different Bones and Analytical Methods on Assessment of Bone Mineralization Response to Dietary P, Phytase, and Vitamin D in Finishing Pigs

Pigs [n = 882; initial body weight (BW) of 33.2±0.31 kg] were used to evaluate the effects of different bones and analytical methods on assessment of bone mineralization response to dietary P, phytase, and vitamin D in growing-finishing pigs. Pens of pigs (20 pigs/pen) were completely randomized to 5 dietary treatments with 9 pens/treatment. After feeding diets for 112-d, nine pigs/treatment were harvested for bone analysis. Treatments were: 1) P at 80% of the NRC STTD P (deficient), 2) NRC STTD P using monocalcium phosphate, 3) NRC STTD P including phytase, 4) Industry P using monocalcium phosphate and phytase, 5) diet 4 with additional 2,000 IU/kg 25(OH)D3 (HyD). All diets contained vitamin D at 1,653 IU/kg. There were no significant differences for final BW, ADG, ADFI, G:F (P>0.10) or non-de-fat bone ash (bone ash×bone interaction, P>0.10). The response to treatment for bone density (Archimedes principle) and bone mineral content (DEXA) tended to depend on the bone (density×bone interaction, P=0.053; mineral density×bone interaction, P=0.157). There were no treatment differences (P>0.10) for bone density and bone mineral density between metacarpals, fibulas, and 2nd ribs. For 10th ribs, pigs fed industry levels of P had increased (P< 0.05) bone density compared with pigs fed NRC levels with phytase, with pigs fed deficient P, NRC P with no phytase, and excess vitamin D from HyD being intermediate. Pigs fed diets supplemented with HyD had increased bone mineral density in 10th ribs compared with pigs fed NRC levels of P with phytase, with pigs fed P deficient diets, industry P without HyD, and NRC P with monocalcium being intermediate. In summary, bone density and bone mineral content responses varied depending on the bone. Differences in bone density and mineral content in response to vitamin D and P were most apparent with the 10th ribs.

Identification of PRRSV cross-neutralizing memory B cells (VIR7P.1062)

Porcine reproductive and respiratory syndrome virus (PRRSV) is widely considered to be the most important pathogen of swine. Yet, there are no vaccines that produce effective broadly neutralizing antibodies to genetically diverse viral genotypes. We recently showed that adult sows develop cross-neutralizing antibodies following infection outbreaks. However, the relevant B-cells producing the cross-neutralizing antibodies have not been identified. Thus, we have characterized surface markers that differentiate porcine B-cell subpopulations and determined their antibody secretion characteristics. Culture of CD21+ B-cells sorted by surface Ig expression showed that surface IgM- and IgG-positive cells proliferated in response to mitogenic stimulation. Sequencing of light and heavy chain variable region mRNA revealed more extensive somatic mutation in the order of plasma cell < IgM-positive < IgG- positive complexity. The CD21+, IgG+ B-cells are putative class-switched peripheral memory B-cells. The isolation of class-switched memory B cells that display cross-neutralizing activity to PRRSV and the subsequent characterization of class-switched memory B cell genetic sequences will allow us to ascertain the necessary somatic mutations that result in the production of PRRSV cross-neutralizing antibodies.