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The provision of sufficient feedstuffs is likely to be the most limiting factor in increasing animal production, apart from other aspects such as breed improvement and disease control. With the continuing shortage of traditional sources of feedstuffs, it is timely to consider underutilized or little-known tree crops which could be used to increase supply of feeds for livestock, particularly in the developing countries.

The effect of the inhibitors 2,4-dinitrophenol (DNP) and g-strophantin (ouabain) on the intestinal uptake and cellular transfer of zinc (Zn) and the effect of the organic ligands histidine and EDTA were studied in vitro with everted intestinal sacs of normally maintained rats. Zn was added to the incubation solution as ZnCl2 or as ZnCl2 mixed with histidine in a molar ratio of 200 : 1 and mixed with EDTA in a molar ratio of 1 : 1 or 10 : 1. The DNP in a concentrationof 0.05 mM proved sufficient to greatly inhibit the uptake and transfer of Zn from the solution containing ZnCl2 mixed with an excess of histidine. DNP also reduced Zn absorption when ZnCl2 alone as added. On the other hand, the presence of DNP in the solution containing ZnCl2 with EDTA was found to increase the transfer of Zn and its ligand. In the presence of EDTA, Zn absorption may, therefore, be controlled by the uptake and transfer of the ligand. Ouabain at the contration of 5 mM and 10 mM greatly reduced Zn uptake by the intestinal wall and the celluar Zn transfer from the solution containing ZnCl2 and histidine. There was only a small effect of ouabain on Zn absorption whether ZnCl2 is added alone or with EDTA. The addition of an excess of histidine as ligand to ZnCl2 in the control groups markedly improved Zn absorption. In contrast to this, the addition of EDTA to ZnCl2 reduces the intestinal Zn uptake and increases the transfer of Zn compared to ZnCl2 alone.