RELATIONSHIP OF HORN FLY TO FACE FLY INFESTATION IN BEEF-CATTLE

Horn fly and face fly counts (n = 394) taken on 194 beef cows represen ting seven breed groups were used to determine the effects of horn fly and face fly counts. Breed groups included were Angus (ANI and ANII), Chianina (CA), Charolais (CH), Hereford (HH), Polled Hereford (PH), a nd Red Poll (RP). The breed group designated ANI consisted of small-fr amed cows. Total horn fly and total face fly counts were determined we ekly on each cow beginning in May and ending in late October or early November in a 3-yr (1988-90) study. Face flies were not counted on the ANI and ANII breed groups in 1988. Ah fly counts were taken when cows were grazing Ozark upland native grass pastures with only containment fences separating breeding groups. No insecticides were used in the s tudy. Data for analysis were the mean annual horn fly and face fly cou nts (averaged across weeks), spring weight and fall weights, gain/day between spring and fall weights, and skin surface area in the spring ( SSAS) and fall (SSAF) for each cow. Relationships among measurements w ere examined by correlation and regression procedures. Horn fly count was correlated (P < .05) with face fly count, spring weight, gain/day, and SSAS (.23, .11, -.25, and .12, respectively). Correlations of hor n fly count with fall weight and SSAF were non-significant. Horn fly c ount, breed, and the breed x horn fly count interaction were significa nt (P < .05) for the face fly regression. Coefficients of regression o f horn fly count on face fly count for ANI, ANII, CA, CH, HH, PH, and RP breed groups were .0361, -.0032, .0201, .0222, .0148, .0514, and .0 363, respectively. Skin surface area in the spring and breed influence d (P < .01) horn fly and face fly count. The breed x SSAS interaction was significant (P < .05) for horn fly count but nonsignificant for fa ce fly count. Coefficients of regression of horn fly count on SSAS wer e 43.80, -27.66, 22.12, 37.73, 21.04, 10.09, and 18.53 for ANI, ANII, CA, CH, HH, PH, and RP, respectively. These data imply that the resist ance/susceptibility of cows to both horn fly and face fly infestations are related and that it differs among breeds. These data also suggest that skin surface area should be accounted for when partitioning vari ation in horn fly counts.