Safety aspects of using iodoform as a methane-mitigating feed additive to dairy cows: Impacts of milk and serum on bovine mammary and human intestinal epithelial cell lines

Ongoing research investigates the use of bromoform and other brominated halomethanes as anti-methanogenic additives for ruminant livestock. Recently, iodoform has shown to be a potent methane inhibitor in dairy cows as well. To evaluate potential associated effects of using iodoform as a feed additive, cell viability assays were conducted using 2 cell lines: bovine mammary epithelial cells (MAC-T) and human intestinal epithelial cells (FHs 74 Int.), representing mammary and intestinal epithelial cell models, respectively. Cells were cultivated in media containing 1, 5 or 10% (vol/vol) of milk whey or blood serum sampled from multi-cannulated (ruminal, duodenal and ileal cannulated) Danish Holstein dairy cows, daily dosed intra-ruminal with iodoform (0 mg/d, 320 mg/d, 640 mg/d, and 800 mg/d). The iodoform dosages were determined based on a previous unpublished pilot study. Moreover, the direct addition of 7 different concentrations (0.003–10 µM) of the pure compounds iodoform, diiodomethane and iodomethane on cell viability of MAC-T were also investigated. Cell viability was increased in both MAC-T and FHs 74 Int. cell lines with increased concentration of serum or whey, whether from control (0 mg/d) or iodoform supplemented cows. No significant linear or quadratic effects of serum or whey were observed on either cell line. Consistent with these findings, MAC-T cell viability was unaffected by exposure to iodoform or its reduced form, iodomethane, across concentrations of 0.003–7 µM. In contrast, diiodomethane reduced cell viability at concentrations > 0.5 µM; however, these levels exceed those expected in vivo following iodoform supplementation. Overall, intra-ruminal administration of iodoform to dairy cows was not associated with adverse effects of serum or whey on MAC-T or FHs 74 Int. cell viability.