Efficacy of a new sustained-release intraruminal selenium bolus

Abstract

Our objective was to test the efficacy of a new sustained-release selenium (Se) bolus versus negative and positive control beef cattle. Fifty-five English breed heifers (mean initial body weight 546ñ46 lb; 248ñ 21 kg) were randomly assigned to one of four treatment groups: one 120-day, sustained-release selenium (Se) bolus on day 0 (A-1X); one 120-day, sustained-release Se bolus on day 0 and a second bolus on day 121 (A-2X); one 365-day, sustained-release Se bolus on day 0 (B); and control (C), no supplemental Se. Heifers grazed Se-deficient native foothill range without any additional supplement. Body weights and blood samples were taken for Se analysis from animals in all four groups at days -28, 14, 28, 49, 63, 121, 183, 293 and 365. No evidence of excess Se intake was observed. Both blood and weight data were analyzed in a model with Se treatment as the main effect; a log transformation for blood Se was used to make variances across treatments similar. Blood Se concentrations were similar amongst treatment groups on day -28. However, on days 14, 28, 49, 63, 121, 183, 293 and 365, blood Se concentrations were higher for the three supplemented groups relative to the control group (P<0.0001). On day 121, Groups A-2X and B had higher blood Se levels than Group A-1X (P=0.0001 and 0.0046, respectively). At days 183 and 293, Group A-2X had the highest blood Se concentrations (231.1ñ22.7 and 133.4ñ13.4 ng/ml), with Groups B (136.8ñ23.0 and 75.8ñ17.9 ng/ml), A-1X (114.3ñ16 and 34.8ñ8.8 ng/ml), and C (21.26ñ2.8 and 15.53ñ2.7 ng/ml) having descending Se blood concentrations, respectively. On day 365, Groups A-2X and B had blood Se concentrations above the 50 ng/ml that is considered deficient. Groups A-1X, A-2X and B gained 25.1, 51.0 and 25.7 lb (11.4, 23.2 and 11.7 kg) more than the 219.6 lb (99.8 kg) gain of the control group (P<0.001). Selenium supplementation provided sufficient mineral to raise blood Se concentrations above deficient levels. When compared with a single 120-day bolus, the single 365-day bolus prevented blood Se concentrations from falling to deficient levels for a longer period of time.