UTILISATION DES PROTÉINES PAR LE VEAU PRÉRUMINANT A L'ENGRAIS. IV. — UTILISATION DES PROTÉINES DE LEVURES D'ALCANES ET INFLUENCE DE L'ADDITION D'UN COMPLEXANT DU FER

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Abstract
The influence of replacing part of milk protein by that of alkane-grown yeast [Candida tropicalis] in milk replacers for preruminant fattening calves was studied. The yeast was cultivated on gas-oil and contained 71% crude protein and 260 ppm Fe. Four milk replacers, in which alkane-grown yeast supplied 26 or 51% of the crude protein, were compared with a control diet in which the proteins were provided almost exclusively by skim milk. Two of the feeds including yeast were supplemented with an Fe-chelating agent (derivative of EDTA). The diets were offered to 16 calves (control feed) or 8 calves (yeast-containing feed) between 3-16 wk old. The health of the animals did not seem to be affected by the origin of the dietary crude protein. The yeast feeds showed a tendency to deposit on the bottom of the pail, without causing large refusals. Although satisfactory, liveweight gains of the calves receiving the diets containing 26 and 51% yeast protein (1144 and 1104 g/day, respectively) were lower (P < 0.01) than those of the valves fed the control diet (1271 g/day). The dry matter intake per kg liveweight gain increased (P < 0.01) with increasing levels of yeast in the diets (1.47-1.57 and 1.61 kg, respectively). The dressing percentage and carcass fat were satisfactory for all the calves, although slightly lower for the groups receiving yeast. The meat color was too dark in those calves fed the yeast containing diets without the Fe-chelating agent. It was satisfactory in all the other cases. The Fe-chelating agent seems to have limited the utilization of dietary Fe. This was confirmed by the hematocrit value of the calves and by the heminic Fe content of the lateral pilars of the diaphragm. Alkane-grown yeast seems well suited for incorporation at a high level into milk replacers for preruminant fattening calves between 3-16 wk old. To avoid a large reduction in animal performances the levels must not exceed 10%, supplying less than 1/4 of the dietary proteins.

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