Effect of parenteral selenium administration to sheep on prevalence and recovery from footrot

Background: Insufficient intake of selenium (Se) is common in many regions, and can contribute to increased susceptibility to and prolonged recovery from infectious diseases. Objective: To determine the effect of Se administration in decreasing the severity and prevalence of footrot in sheep. Animals: Thirty-eight footrot-affected and 19 nonaffected sheep from a commercial flock of known high incidence of footrot. Methods: Placebo-controlled, prospective, 15-month clinical trial. Footrot-affected sheep were randomly assigned into 2 groups (n=19) and injected with either 5mg Se (footrot [FR]-Se) or saline (FR-Sal) at 1-month intervals for the duration of the study. Unaffected sheep (controls) received no treatment. Sheep feet were examined, trimmed, and scored for footrot with a scale of 0 (no footrot) to 4 (extensive) at 0, 3, 6, 9, and 15 months. Sheep were also bled at time 0 and then at 3, 6, and 15 months to assess whole blood Se concentrations. Results: At time 0, control sheep (255 ± 11ng/mL) had higher (P < .05) whole blood Se concentrations compared with FR-Se (205 ± 12ng/mL) and FR-Sal (211 ± 14ng/mL) sheep. By 6 months, FR-Se sheep (317 ± 9 ng/mL) had whole blood Se concentrations greater (P < .05) than both control (281 ± 14ng/mL) and FR-Sal (277 ± 16ng/mL) sheep. FR-Se ewes showed a faster decline in highest lesion score at 3 (P=.012) and 6 (P=.0036) months, and a greater decrease in the number of feet with foot score >0 at 6 (P=.020) months compared with FR-Sal ewes. Sheep with blood Se concentrations <300 ng/mL were at 3.5 times greater risk (1.1-12.1 confidence interval, odds ratio) for FR, although this relationship was only significant (P=.04) at 6 months of the study. Conclusions and Clinical Importance: In sheep with footrot, improved Se status in conjunction with routine control practices result in more rapid improvement of foot lesions.