[The nutritive defaunation of the rumen in ruminants].

Two promising methods to remove the ciliate protozoa of the stomach of ruminants by simple alterations in the feeding system were examined in vivo with lambs and heifers in the present investigation. The use of pelleted concentrates fed ad libitum and of milk, especially of milk fat (cream), turned out to be effective against protozoa when given after few hours of fasting. Milk led to the defaunation of a great proportion of the animals supplied all at once in an amount of 5-10% of rumen fluid volume. With cream the amount could be lower according to the higher fat content. Defaunation with concentrate was found to be not dangerous only for animals adapted to intensive feeding sufficiently. Additionally, a series of in vitro experiments were carried out to evaluate the reasons for the anti-protozoal effects of these methods. Concentrates rich in starch had toxic effects against protozoa, which mainly derived out of the depression in ruminal pH. The formed lactic acid had further effects irrespective of pH. The addition of crude fibre, especially of cellulose or lignin, reduced or prevented the anti-protozoal effects of concentrate fed ad lib. This was not so with the addition of buffers. With milk the included fat was shown to be responsible for the anti-protozoal effects, while the other main constituents of milk were of no importance.