Selenium metabolic status and response to supplementation in grazing Chilean-Criollo horses

Objective. Two experiments were conducted to determine the selenium status in grazing Chilean-Criollo horses and evaluate their response to a Na2SeO3 supplement. Material and methods. (Exp.1)The blood activity of glutathione peroxidase (GPx, EC.1.11.1.9) (AcGPx) was determined in horses kept grazing in 10 breeding farms from the south of Chile: PO, n = 40 horses were kept grazing during autumn (PO), 47 horses were kept grazing during autumn and supplemented with oat grain (PO + A), and 23 horses were kept grazing during spring (PP). (Exp.2)23 horses kept on pasture were allotted into three groups: G1, n = 7, supplemented with a dose of Na2SeO3 (Se = 0.05mg/kg bw, im) on day 0; G2, n = 8, supplemented with similar doses of Na2SeO3, on days 0 and 15; and GC, n = 8, control. AcGPx was determined on days 0, 30 and 120. Results. Median (Me) of the AcGPx on all the farms were below the adequate limit ( > 130 U/g Hb), being higher in PO + A (Me = 92, P-25% = 47, P-75% = 129 U/g Hb) and PP (Me = 85, P-25% = 45, P-75% = 114 U/g Hb) than PO (Me = 35, P-25% = 20, P-75% = 85 U/g Hb) (p < 0.05). Initial AcGPx was similar and below adequate in the three groups and increased after Na2SeO3 administration (p < 0.05) in G1 (121 +/- 52 U/g Hb) and G2 (124 +/- 69 U/g Hb). Conclusions. A deficiency is observed in Chilean-Criollo horses grazing during autumn and spring in southern Chile, parenteral administration of Na2SeO3 (0.05mg/kg bw) in single or double doses improves the Se status without achieving adequate values