Intramuscular Selenium Administration in Selenium‐Deficient Cattle

Nine recently weaned Hereford heifers were randomly assigned to a control group (n = 3) or a treatment group (n = 6). The animals were selenium (Se) deficient (mean ± SD blood Se concentration = 0.024 ± 0.012 μg/mL). They were maintained on a selenium‐deficient diet, and on day 0 of the study the treatment group was given 0.05 mg Se/kg body weight intramuscularly, while the control group received a placebo. The Se concentration of blood, serum, and urine as well as the glutathione peroxidase (GSH‐Px) activity of blood and serum was measured over an 84‐day period. Peak blood Se and serum Se concentrations (mean ± SD) in the treatment group occurred at 5 hours postinjection and were 0.131 ± 0.028 μg/mL and 0.154 ± 0.027 μg/mL, respectively. The mean blood Se concentration of the treatment group was greater ( P < .05) than that of the control group for the first 28 days after injection. The mean serum Se concentration of the treatment group was greater ( P < .05) than that of the control group for all times after injection, except for day 56. The mean (±SD) blood GSH‐Px activity of the treatment group (12.0 ± 2.3 mU/min/mg hemoglobin) was increased ( P < .05) over the control group (2.0 ± 1.4 mU/min/ mg hemoglobin) by day 28 and continued to be greater ( P < .05) throughout the 84 day postinjection period. The blood GSH‐Px activity and the blood Se concentrations in the treatment group heifers did not reach concentrations considered indicative of Se adequacy (30 mU/min/mg hemoglobin and 0.10 μg/mL, respectively) except briefly, at 5 hours postinjection when the blood Se concentration of the treatment group was 0.131 ± 0.028 μg/mL. The mean serum GSH‐Px activity of the treatment group did not differ at any time from that of the control group ( P ≥ .17). The mean (±SD) fractional excretion (FE) of Se, as an estimate of Se excretion, was greater ( P < .05) in the treatment group heifers (n = 5; 6.2 ± 2.5%) than in the control heifers (n = 3; 1.3 ± 0.6%) at 24 hours postinjection. The mean (±SD) weight gain, from day 0 to day 84, for the treatment group heifers was 63.0 ± 18.1 kg and the mean weight gain for the control group heifers was 53.1 ± 7.3 kg at 84 days postinjection and there was no difference between the groups ( P < .39). Conclusions drawn from this study include: 1) the increase in blood GSH‐Px activity occurs approximately 28 days after Se injection given to Se‐deficient heifers, 2) a single label dose of injectable Se does not result in blood Se concentrations or blood GSH‐Px activity normally considered to be adequate, 3) the label dose of injectable Se, although therapeutically beneficial for nutritional myodegeneration (NMD), does not seem to be a desired method for long‐term Se supplementation of cattle consuming a Se‐deficient diet, and 4) blood Se is a better predictor of Se status than serum Se. (Journal of Veterinary Internal Medicine 1993; 7:342–348. Copyright © 1993 by the American College of Veterinary Internal Medicine.)