During 1995, a clinical trial was performed to evaluate the medical and economical effects of ivermectin administration for grazing heifers at one public farm, Saitama prefecture. Animals, which were entered for the grazing in spring, were classified into 3 blocks (A, B, C) based on their age and body weight. In each block, animals were randomly allocated into administration (5 times ivermectin injections) and non-administration groups . Daily body weight gain, hematocrit values, number of animals with
Theileria infections, conception rates and economical effects were evaluated between two groups. In low age block, animals with ivermectin administration had significantly higher daily body weight gain and hematocrit values compared to nonadministrated animals, however, no significant differences were observed in the number of animals with
Theileria infections and conception rates. In other age blocks, improved daily body weight gain were constantly observed in ivermectin administrated groups, however, no statistical differences were detected. Because of the improved daily body weight gain, the management strategy using ivermectin administration was economically useful for the grazing heifers, especially when it was used for young animals.
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