An Investigation of the Cattle Louse Problem1

Abstract

In a study on gains in weight versus louse infestations, 30 of the lousiest feeder heifers in a feed lot containing approximately 3,000 were selected. Two lots of 10 each were sprayed with insecticides for louse control, and the third was sprayed with water. After 42 days gains in weight of the treated lots were not significantly different from those of the control lot. Before treatment, louse infestations averaged light to moderate on all lots; 37 days after treatment, infestations in the control lot averaged very light to light, and only four lice were found in the two treated lots. A Hereford steer, very heavily infested with Haematopinus eurysternus (Nitzsch), under close observation for 4½ months, developed severe anemia, and would have died in the absence of louse control. When the lice were destroyed he improved markedly in gains in weight and feed efficiency. Rancher surveys, cattle buyer records, and population studies on slaughter cattle, indicated that infestations of this magnitude, although they occur regularly throughout Montana, do not ordinarily affect more than 1% or 2% of the cattle. Infestations on the rest of the population are probably of minor economic significance. Louse population studies on the freshly removed hides of 3,188 slaughter cattle indicated that in Montana, Herefords are most frequently and most heavily infested, and that Angus are least so; that H. eurysternus is economically the most important species, followed in order by Linognathus vituli (L.), Solenoptes capillatus End., and Damalinia bovis (L.); and that different breeds of age classes of cattle tend to he infested differently by the four different species of lice. From a n economic standpoint, louse control measures are probably justified on 5%, or fewer, of the cattle in Montana.