A Three-Year Study on the Effect of Fly Control on Milk Production by Selected and Randomized Dairy Herds 1

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Abstract
During the three consecutive summers of 1957, 1958, and 1959,99 lactating cows were used to test the effect of fly control on milk production under varied farm conditions on three farms in Centre County and Northumberland County, Pa. On the University and Tilford farms, the animals were selected on the basis of milk production, stage of lactation, body weight, age, and general physical condition; these were divided into two similar groups, the treated and untreated, which were managed alike throughout the trials. On the X Farm, two randomized herds served as treated groups and a third one as the untreated control; no attempt was made to equalize the management of the three randomized herds. The flies on the three farms were the horn fly, Haematobia irritans, the stable fly, Stomoxys calcitrans, the horse flies, Tabanus sulcifrons(Macquart) and T. giganteus (DeGeer), the house fly, Musca domestica, and the face fly, Musca autumnalis DeGeer. Treatments for fly control included the use of spray and aerosol formulations containing various combinations of such principal ingredients as methoxychlor, dimethoate, synergized pyrethrins, R-1207 (3-chloropropyl n-octyl sulfoxide), MGK R-326 (di-n-propyl isocinchomeronate), butoxy polypropylene glycol, diethyl-toluamide, and Thanite (isobornyl thiocyanoacetate, 82%, other related terpenes, 18%). The formulations were applied by means of two automatic devices: an electric-eye-controlled sprayer consisting of a pipe system with 10 nozzles, a photoelectric relay unit, and pump-motor assembly; and a automatic photoelectric aerosol applicator (also known as automatic photoelectric device) equipped with a triggering mechanism for releasing aerosol from containers. Cows were sprayed once daily after milking, as they passed through the doorways or chutes at which the devices were mounted. Milk production records were kept during the treatment period as well as the pretreatment and posttreatment periods, except on the Tilford Farm. These tests showed that under the conditions prevailing in this investigation, fly control did not have significant effect on milk production by the selected herds on the University and Tilford Farms, which were well managed and liberally supplied with supplementary feeds. This was consistently true throughout the three seasons regardless of the differences in the degree of fly infestation, ranging from heavy to light, or in the effectiveness of treatments, varying from excellent to unsatisfactory. It also appeared that neither the absorption of small amounts of methoxychlor by the treated cows nor repeated applications of oil-based sprays had adverse effect on milk productivity of the animals concerned. Of the six selected or randomized herds receiving spray or aerosol treatments, only one randomized herd on the X Farm showed favorable response; the average daily decrease in milk production in this herd, which was poorly managed and supplied with very scanty pasture and limited supplements, was significantly less than that in the untreated control. Statistical analyses indicated that the decrease in milk production by the treated herd was approximately one-third that of the untreated. Findings of the 3-year study lead to the suggestion that among the factors involved in determining the effect of fly control on milk production, herd management with particular reference to the supply of pasture and supplements could play a dominant role.