Horn fly, Haematobia irritans (L.), population estimates often serve as a diagnostic tool prior to implementing managerial control options available to researchers and producers. Digital photographs taken of cattle infested with horn flies have been suggested to provide similarly accurate population estimates as compared with traditional visual assessments. The objective of this study was to compare visual and digital techniques used to estimate horn fly populations. Sixteen Angus × Hereford yearling heifers artificially infested with four levels of horn flies (Low = 0 flies; Medium = 250 flies; High = 500 flies; Extreme = 1,000 flies) were evaluated. Population estimates were taken visually by experienced (VE1) and inexperienced (VE2) technicians, as well as digitally, with photographs taken on both lateral sides of the south-facing animal. Horn flies were counted in both photographs and combined (CDC) for full body estimates. In addition, the highest photographed side population times two (DDC) was used for comparison. Estimations were made at 0700, 1200, and 1900 h the day following infestation. A time of observation × infestation level interaction (P < 0.01) was detected. On average, VE1 population estimates were greater (P < 0.01) than any other counting method observed. Morning estimates were greater (P < 0.05) than those taken at noon or in the early evening regardless of counting method. Further research regarding the standardization of these techniques to ensure more accurate population estimates is needed before these methods can be incorporated into integrated pest management programs.

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Twenty-four Holstein heifers (165.6 kg ± 5.1 kg initial BW) were utilized in a complete randomized design. The objective was to evaluate effects of supplemental Zn source on growth, reproductive development, and immunocompetence of replacement Holstein heifers. Heifers were randomly allotted to one of two treatments: supplemental zinc sulfate (ZnSO4) or supplemental zinc methionine (ZnMet). Dietary Zn averaged 78.5 ppm for ZnSO4 heifers and 86.3 ppm for ZnMet heifers. Weights and blood were collected once weekly. On d 85 heifers were inoculated with ovalbumin to assess immunocompetence. Follicular aspirations and reproductive tract scores (RTS) were taken on d 106. Liver biopsies and body measurements were collected on d 133 and d 259. Source of Zn did not affect (P ≥ 0.54) BW, DMI, ADG, or G:F. Body measurements were similar (P ≥ 0.28) between treatments. Treatment groups did not differ in RTS, ovarian area, or follicle size or number (P ≥ 0.14). Concentration of progesterone, estradiol, and ratio of progesterone to estradiol of follicular fluid were not affected (P ≥ 0.40) by Zn source. Heifers pubertal prior to synchronization, heifers pregnant per service, total services to pregnancy, and percent heifers pregnant at conclusion of the study (P ≥ 0.34) were not different between treatments. Liver mineral concentrations (P ≥ 0.55) were not affected by Zn source. Circulating Zn in serum did not differ on either d 1, d 141, or d 252 (P ≥ 0.36) for either treatment. Heifers supplemented with ZnMet demonstrated a greater (P = 0.02) antibody response 14 d after initial ovalbumin vaccination than ZnSO4 heifers. By d 14 after second inoculation, immune response was similar (P = 0.38) for both treatments. These results suggest that in the absence of stress, ZnMet enhances immunocompetence of replacement Holstein heifers but has no effect on growth or reproductive development.

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