Food-chain contamination by arsenic (As) is a newly uncovered disaster. Effects of As-contaminated drinking water and paddy straw on the excretion of As through milk, urine, and dung of dairy cows (n = 240) were studied in As-prone areas of Bangladesh. Mean (±SEM) total As (inorganic plus organic) concentration in drinking water, paddy straw [dry weight dw)], cow's urine (specific gravity adjusted to 1.035), dung (dw), and milk (wet weight) were 89.6 ± 6.5 μg/l, 1,114.4 ± 57.3 μg/kg, 123.6 ± 7.6 μg/l, 1,693.0 ± 65.1 μg/kg, and 26.2 ± 2.8 μg/l, respectively. Significantly (p < 0.01) greater As was in Boro straw (1,386.9 ± 71.8 μg/kg) than Aus (702.4 ± 67.1 μg/kg) and Aman (431.7 ± 28.8 μg/kg) straw and in straw irrigated with shallow (1,697.3 ± 81.9 μg/kg) than deep well water (583.6 ± 62.7 μg/kg) and surface water (511.8 ± 30.0 μg/kg). Significant (p < 0.01) positive correlations were found between As contents of cow's urine and drinking water (r = 0.92) as well as cow dung and straw (r = 0.82). Concentrations of As in cow urine, dung, and milk were increased with the relative increment of As in drinking water and/or straw. These results provide evidence that dairy cows excrete ingested As mainly through urine and dung; thus, As biotransformation through milk remains low. This low concentration of As in milk may be of concern when humans are exposed to multiple sources of As simultaneously. Moreover, As in cow dung could be an environmental issue in Bangladesh.