THE EFFECT OF ZINC-DEFICIENCY AND APPLICATION OF RECOMBINANT BOVINE GROWTH-HORMONE ON PLASMA GROWTH-HORMONE AND INSULIN-LIKE GROWTH FACTOR-I OF CALVES

In a fifteen week breek- and a ten week fattening experiment with calves, bot a control group an a zinc deficient group were treated with exogen bovine growth hormone. For that purpose 48 male Brown Swiss calves were distributed to four treatments and housed in individual boxes. The animals of the breed epxeriment maintained a milk replacer for the first seven weeks with a zinc content of 6.7 mg/kg and for the whole experiment a basal diet with 7.8 mg zinc/kg. The zinc content of the milk replacer in the fattening experiment was 5.7 mg zinc/kg. Blood samples were taken in the weeks, 1, 13 and 15 in the breed experiment and in the week 10 in the fattening experiment by puncture of the jugular vain using the vacutainer system. In these blood samples growth hormone and insulin like growth factor-1 were analysed. The concentration of growth hormone was neither in the breed- nor in the fattening experiment influenced by the low zinc intake and the application of exogene bovine growth hormone. This results show, that not a reduced concentration of growth hormone is responsible for the reduced growth due to zinc deficiency. The concentration of the insulin like growth factor-1 decreased in the breed experiment due to zinc deficiency about 54% for the not with exogene growth hormone treated animals and about 21% for the treated animals. In the fattening experiment the reduction amounted to 69% respectively 48% due to zinc deficiency. The application of exogene growth hormone increased the insulin like growth factor-1 in the breed experiment about 20% when the zinc intake was high and about 104% when the zinc intake was deficient. In the fattening experiment the increase amounted to 17% respectively 92% for the deficient animals. So possibly a reduced concentration of plasma insulin like growth factor-1 is responsible for the growth retardation seen during zinc deficiency.