Drinking water can contain high concentrations of ferrous iron (Fe2+), which is more absorbable than ferric iron (Fe3+) found in feed and may negatively impact cow health and productivity. Our objective was to characterize Fe status, oxidative stress, and drinking water preference of lactating dairy cows in response to different concentrations, valences and sources (salts) of Fe. In two dosing experiments, cows were abomasally administered 0, 0.75, or 1.5 mg Fe/kg bodyweight from ferrous lactate; or, 0 or 1.5 mg Fe/kg bodyweight from ferrous or ferric sulfate. Blood was sampled hourly for 12 h, and liver biopsies were taken at 0, 18 and 36 h post-dosing. The Fe dosed had minimal effects on Fe status or oxidative stress, suggesting that amounts of Fe administered do not affect short-term Fe metabolism. A protocol was developed to evaluate water preference and drinking behavior of lactating cows for subsequent experiments. In four preference experiments, cows were offered pairs of drinking water treatments. Water intake was measured to determine preference for water with Fe of different concentrations, valences and sources. Water intake was not different between 0 and 4 mg Fe/L from ferrous lactate, but intake with 8 mg Fe/L from ferrous lactate was reduced. Water intakes of treatments with 8 mg Fe/L from ferrous lactate, sulfate or chloride were less compared with control water, but not different among Fe sources. Direct metal analysis commonly used to determine Fe content of drinking water for livestock greatly underestimates total recoverable Fe (acid digested water sample). Total recoverable Fe values as used in our research are listed above.
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