Abstract #83

# 83
Prepartum dietary cation-anion difference (DCAD) and 25-hydroxyvitamin D3 supplementation modulate β-defensin responses in postpartum dairy cattle.
Kathryn Merriman*1, Natalia Martinez1, Rachel Rodney2, Jessi Powell1, Mercedes Kweh1, Nathaniel Elliott1, Jose Santos1, Corwin Nelson1, 1University of Florida, Gainesville, FL, 2SBScibus, Camden, Australia.

Postpartum hypocalcemia has been associated with suppressed neutrophil and lymphocyte function in dairy cattle. It was hypothesized that mitigation of postpartum hypocalcemia would enhance activation of host-defense mechanisms during the postpartum period. The objective of this study was to determine the effects of pre-partum DCAD in combination with vitamin D supplementation on expression of a cluster of β-defensin (DEFB) host-defense genes. Pregnant dry Holstein cows (n = 51, multiparous) of 255 d gestation were blocked by parity and randomly assigned to 4 prepartum diets of positive (+130 mEq/kg) or negative (−130 mEq/kg) DCAD and either 3 mg vitamin D3 or 3 mg of 25-hydroxyvitamin D3 (25D) per 11 kg of DM/d. Treatment diets were fed for the last 21 d of gestation, and, upon calving, cows were fed the same lactation ration for the first 49 DIM. Peripheral blood neutrophils and monocyte cultures were collected at d 0 and d 3 of calving and stimulated with 75 ng/mL of 25D and a combination of 100ng/mL of lipopolysaccharide (LPS) and 75 ng/mL of 25D. The mRNA transcripts of DEFB genes were quantified by real-time PCR, and data were analyzed with a general linear mixed model to test for fixed effects and interactions of experimental variables. Neutrophil gene expression of DEFB4 (P ≤ 0.05), DEFB5 (P ≤ 0.05), DEFB7 (P = 0.1), and DEF10 (P = 0.1) was greater in cows fed the negative DCAD. Neutrophils had lower expression of DEFB3, DEFB4, DEFB7, DEFB10, and lingual antimicrobial peptide in response to LPS at d 3 of calving compared with d 0, (P ≤ 0.05). Cows supplemented with vitamin D3 showed greater DEFB3, DEFB4, DEFB5, DEFB7, and DEF10 gene expression in monocytes (P ≤ 0.05) than 25D supplemented cows. In conclusion, pre-partum DCAD and 25D affect neutrophil and monocyte β-defensin responses and have implications for improving transition cow immunity.

Key Words: defensin, DCAD, vitamin D