Abstract A series of trials was carried out to determine the effect of a high intake of iron as Fe(OH)3, derived from irrigation water high in iron, upon the health and production of dairy cows, and to determine, if possible, the maximum safe intake of iron from this source. High iron intake caused scouring, loss of bodyweight, and lowered production of milk and butterfat. Iron intake below 30 g/day affected milk yield and digestibility of ingested herbage, and between 30 and 60 g/day lowered butterfat yield and caused losses of bodyweight.