0.05). Heifers showed a lower activity for GSH-Px than cows in both periods (p<0.05). Twenty percent of the animals showed a low activity of GSH-Px (below 60 U/g Hb), meaning a Se deficiency in the animals. There was a relation between the content of Se in forage and the blood activity of GSH-Px in heifers (r= 0.74; p<0.05). Accordingly, the content of Se in most of the forage produced in the dairy cattle area from the IXth Region, Chile is below the nutritional requirements for grazing dairy cattle and nutritional metabolic deficiencies of Se are present in dairy herds according to blood activity of GSH-Px. Heifers are mostly affected]]>
The objective of this study was to evaluate the effect of selenium (Se) supplementation on milk somatic cell count (SCC) in dairy cows. Twelve multiparous Holstein-Friesian cows were fed a diet containing a suboptimal Se concentration (<0.05 ppm, dry basis) starting 2 months before calving. Supplemented cows (n=6) received a single s.c. injection of barium selenate (1 ml/50 kg BW) 45 days prior to calving, whereas control group was kept unsupplemented. Twenty weeks after calving, two mammary quarters (right side) of each cow were challenged with 205,000 cfu/ml of Staphylococcus aureus (strain Newbould 305). Blood was collected bi-weekly until day 150 of lactation for the analysis of blood glutathione peroxidase (GPx1; EC 1.11.1.9) activity. To re-isolate the challenging pathogen and to evaluate SCC, aseptic milk samples were collected daily starting on the day of challenge, and finishing 7 days after inoculation. Unsupplemented cows had a lower activity of GPx1 through the experiment (P<0.001). Natural log SCC (lnSCC) was higher in unsupplemented than Se-supplemented cows (P=0.04), showing evidence of significance after 5 days. Selenium supplementation of dairy cows fed a diet containing a suboptimal Se concentration, resulted in higher blood activity of GPx1, and lower mean lnSCC after an intramammary challenge with Staph. aureus.
RESUMEN -Con el objeto de validar una técnica para determinar la actividad sanguínea de glutatión peroxidasa (GSH-Px; EC 1.11.1.9) en el Laboratorio de Patología Clínica de la Universidad Austral de Chile y establecer la correlación entre su actividad y la concentración sanguínea y plasmática de selenio (Se) en bovinos a pastoreo en rebaños lecheros del sur de Chile, se tomaron 5-10 mL de sangre heparinizada a 112 vacas de ocho rebaños en la provincia de Valdivia. La actividad enzimática se analizó mediante una técnica cinética, y el Se por activación de neutrones. Fueron calculadas la inexactitud e imprecisión de la técnica cinética y se describen el rango, promedio y desviación estándar de la actividad enzimática. La correlación entre la actividad sanguínea de GSH-Px y la concentración de Se fue obtenida mediante el coeficiente de correlación simple. La inexactitud e imprecisión fueron 5,9% y 10%, respectivamente. La actividad de GSH-Px fue 89 ± 45 U/g de hemoglobina (Hb) y la correlación entre las variables señaladas fue r=0,97 (P<0,05). Según estos resultados, es posible recomendar el uso rutinario de la técnica descrita. La correlación señalada permite anotar que en bovinos a pastoreo la actividad de GSH-Px está relacionada con la concentración sanguínea de selenio.Términos para índice: antioxidantes, estrés oxidativo, minerales.
BLOOD ACTIVITY OF GLUTATHIONE PEROXIDASE AND ITS CORRELATION WITH BLOOD SELENIUM CONCENTRATION IN GRAZING DAIRY CATTLEABSTRACT -Selenium (Se) is part of the antioxidant enzyme glutathione peroxidase (GSH-Px; EC 1.11.1.9) structure, whose blood activity is related to the blood level of selenium. This study was designed to validate the analytical method to analyze the GSH-Px blood activity at the Clinical Pathology Laboratory of the Universidad Austral de Chile, and to correlate it with blood Se level in dairy cattle from the South of Chile. Blood heparinized samples were taken from 112 dairy cows from eight dairy herds located at Valdivia province, Chile. A kinetic NADPH-dependent technique was used to analyze the blood GSH-Px, and the content of Se in blood and plasma was analyzed by neutron activation. The Se concentration in blood was analyzed in 12 samples to correlate GSH-Px blood activity with blood and plasma Se level. The inaccuracy and imprecision were 5.9% and 10%, respectively. The mean and standard deviation of the obtained values were 89 ± 45 U/g of hemoglobin (Hb). The correlation between blood selenium and blood GSH-Px activity was r=0.97 (P< 0.05). Accordingly, it is possible to analyze the blood activity of GSH-Px by using the described technique. The blood activity of GSH-Px was related to the blood selenium level.
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