care is also required in interpreting concentration data, since the processes described are not always similar,the animal type and size varies widely and concentrations are inevitably influenced by water consumption. the best basic for expressing and comparing pollution output and water use is the use of an equivalent dressed carcass weight, since comparison of data between mixed species facilities and animals of different carcass weights is then possible. unfortunately, data are rarely published in this form and the latest published figures remain those of Witherow, 1973 (table 3,).