The purpose of this study was to determine the clinical effectiveness of selenium (Se) supplementation on foot rot (FR) prevalence and recovery in sheep. A prospective, 15-month, placebo-controlled clinical trial was undertaken in a commercial sheep flock.
FR-affected sheep were randomly divided into 2 groups (n=19). An additional control group of 19 sheep without FR (Control) were identified. Sheep feet were examined, trimmed, and scored for FR using a scale of 0 (no lesions) to 4 (extensive lesions). Half the FR-affected sheep were treated with 5 mg injectable Se (FR-Se) at 1-month intervals for the duration of the study; the other half were given saline injections (FR-Sal). Controls received no treatment. Sheep feet were reexamined, trimmed and rescored at 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. Whole-blood Se data were analyzed by ANOVA for repeated measures; foot scores were assessed by nonparametric analyses with main effects of month and treatment.
At time 0, Control sheep (255 ng/ml) had higher (P<0.05) whole blood Se concentrations compared with FR-Se (205 ng/ml) and FR-Sal (211 ng/ml) sheep. By 6 months, FR-Se sheep (317 ng/ml) had whole blood Se concentrations greater (P<0.05) than both Control (281 ng/ml) and FR-Sal (277 ng/ml) sheep. FR-Se ewes showed a faster decline in highest lesion score at 3 (P=0.05) and 6 (P=0.03) months, a greater decrease in the number of feet with foot score >0 at 6 (P=0.02) months, and a tendency for a lower total severity score at 6 (P=0.07) 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 CI, Odds Ratio) for FR, though this relationship was only significant (P=0.04) at 6 months of the study.
In sheep with FR, Se supplementation results in higher whole-blood Se levels and more rapid improvement of foot lesions compared with saline treatment.