60 - The Effect of Neomycin Inclusion in Milk Replacer on Gut Health and Development in Preweaned Male Holstein Calves

Neomycin is commonly used in calf milk replacers (MR) to prevent diarrhea, however, antimicrobial exposure in early life may have consequences to gut development. The objective of this study was to investigate the effects of neomycin inclusion in MR on calf gut health and development. Thirty-six calves were randomly assigned to one of three treatments: control (CON), non-medicated (MR, n = 12), short-term antimicrobial exposure (ST: 20 mg/kg BW neomycin mixed in MR from d 1-14, n = 12), or long-term antimicrobial exposure (LT: 20 mg/kg BW neomycin in MR from d 1-28, n = 12). Fecal samples were collected weekly to measure total bacteria, and gut permeability was measured in week 2 and 4 by comparing serum recovery of orally dosed lactulose and D-mannitol markers. Calves were dissected at week 5 to collect intestinal tissues, which were used to analyze histology, gene expression and total bacteria abundance. Digesta samples were collected to analyze for total bacteria abundance and volatile fatty acid (VFA) concentrations. No treatment effects were found in the amounts of total bacteria in fecal, digesta, or tissue samples. Marker recovery in serum was higher at week 2 compared to week 4 (P < 0.01), suggesting that calves in early life have higher gut permeability. Histomorphological measures were similar, except for villi length in the distal jejunum, which was longest in ST calves (P = 0.05). Tight-junction, mucus, and inflammatory-associated gene expression was similar overall, although the expression of Tight junction protein-1 in the distal jejunum was lowest in CON calves (P = 0.04). Distal jejunum acetic acid, propionic acid, and total VFA tended to be highest in LT calves (P = 0.09; P = 0.06; P = 0.07, respectively). Although this study found few consequences of neomycin to gut health, the lack of benefits supports the argument that antimicrobials should be used prudently.