Chromium (Cr) has been studied since the end of the 19 th century, when carcinogenic effects of hexavalent Cr were discovered. Essentiality of trivalent Cr was demonstrated in 1959; Cr 3+ has been studied in humans and laboratory animals since the 1970s and it is only since the 1990s that Cr has been studied as an essential element in livestock animals with the same intensity. Trivalent chromium is essential to normal carbohydrate, lipid and protein metabolism. Chromium is biologically active as part of an oligopeptide -chromodulin -potentiating the effect of insulin by facilitating insulin binding to receptors at the cell surface. With chromium acting as a cofactor of insulin, Cr activity in the organism is parallel to insulin functions. Cr absorption is low, ranging between 0.4 and 2.0% for inorganic compounds while the availability of organic Cr is more than 10 times higher. Absorbed Cr circulates in blood bound to the β-globulin plasma fraction and is transported to tissues bound to transferrin. Absorbed Cr is excreted primarily in urine, by glomerular filtration; a small amount is excreted through perspiration, bile and in milk. The demand for Cr has been growing as a result of factors commonly referred to as stressors, especially during different forms of nutritional, metabolic and physical strain. This review describes Cr metabolism, the different biological functions of Cr and symptoms of Cr deficiency.

Selenium concentration and activity of glutathione peroxidase (GSH-Px) as direct and indirect indicators of selenium status were determined in whole blood samples collected from 326 cattle in 30 herds kept in various regions of the Czech Republic. The GSH-Px activity in the samples was measured by the UV method, using the set supplied by Randox. Selenium in the sample was measured using the hydride technique AAS. The two variables showed a close and significant correlation (r = 0.90; p < 0.01). The regression line, defined by the equation y = 6.44x + 21.4, allowed us to determine the GSH-Px activity of 665.4 µkat . l -1 as equivalent to selenium concentration in whole blood 100 µg . l -1 . Mean selenium concentration and mean GSH-Px activity found in whole blood samples were 78.25 ± 46.67 µg . l -1 and 525.51 ± 335.56 µkat . l -1 , respectively. Insufficient or marginal supply of selenium was diagnosed in 64% of the animals in terms of selenium concentration, in 63% of the animals in terms of GSH-Px activity and in 55% of the animals with selenium concentrations <100 µg . l -1 and GSH-Px activity < 665.4 µkat . l -1 . In this study, close dependence of GSH-Px activity and selenium concentration in the blood of cattle was found. Activity values of GSH-Px were determined for the use in diagnosis of insufficient selenium in cattle in the Czech Republic.

Ludvíková E., L. Pavlata, M. Vyskoãil, P. Jahn: Selenium Status of Horses in the Czech Republic. Acta Vet. Brno 2005, 74: 369-375.The aim of this study was to determine the relation between selenium concentration and activity of glutathione peroxidase (GSH-Px, EC 1.11.19) in whole blood of horses, reference ranges for the activity of GSH-Px and to evaluate the selenium status of horses in the Czech Republic. Blood samples were collected from 159 horses from 35 different farms and processed using the AAS and photometric methods to determine concentrations of selenium and the GSH-Px activity, respectively. Data on both parameters were processed using correlation and regression analysis in order to obtain reference values of GSH-Px for the indirect evaluation of the selenium status of horses. The results were also used to evaluate the occurrence of selenium deficiency in the horses examined. A highly significant linear relation was found between both variables. It can be expressed using the Spearman's coefficient of rank correlation (r s = 0.873; p < 0.01) and the regression equation (y = 3.621x -28.698; p < 0.01, r = 0.842). The value of 75 µg·l -1 of selenium in whole blood is considered as a threshold of selenium deficiency in horses. According to our results, the corresponding level of the activity of GSH-Px useful in the diagnostics is 200 µkat·l -1 . Using these criteria, there was a high prevalence of selenium deficiency in the collection of horses examined amounting to 47% and 48% when evaluating the selenium status by the selenium concentration and the activity of GSH-Px, respectively. It can be concluded that there is a high correlation of the activity of GSH-Px and selenium concentration in whole blood of horses and that reference values of the activity of GSH-Px useful in the diagnostics of selenium deficiency in horses in the Czech Republic were determined. The occurrence of selenium deficiency in horses is a topical problem in the Czech Republic.

The aim of the work was to assess the effects of supplemental chromium (Cr) on metabolism of dairy cows in the peripartal period. Rations fed to dairy cows in a herd of Holstein cattle with mean milk yield of 7 500 l were supplemented with chromium-enriched yeast (Co-Factor III Chromium Yeast, Alltech, 0.1% Cr 3+ ) at 10 mg of Cr per animal per day. The treatment was started 21 days before the expected delivery date and discontinued 30 days after the delivery. Blood and urine samples were collected from ten experimental and ten control cows at weekly intervals, the state of health was monitored by regular clinical examinations, and milk yield for the first 100 days of lactation was recorded. The results indicate favourable effects of the supplementation on energy metabolism. The Cr-supplemented cows showed significantly higher blood glucose concentrations at post-partum (p.p.) weeks 4 (4.25 ± 0.21 vs. 3.74 ± 0.36 mmol·l -1 ; p < 0.01) and 5 (4.06 ± 0.41 vs. 3.64 0.28 mmol·l -1 ; p < 0.05) and lower ketone bodies concentration at p.p. week 4 (0.88 ± 0.11 vs. 1.38 ± 0.66 mmol·l -1 ; p < 0.05). The Cr-supplemented cows showed also significantly lower bilirubin concentration at p.p. week 2 (3.93 ± 0.84 vs. 6.47 ± 3.25 µmol·l -1 ; p < 0.05) and lower catalytic activities of aspartate aminotransferase at p.p. weeks 3 (1.37 ± 0.14 vs. 1.66 ± 0.20 µkat·l -1 ; p < 0.01) and 5 (1.16 ± 0.08 vs. 1.47 ± 0.18 µkat·l -1 ; p < 0.01) and lactate dehydrogenase at p.p. week 5 (27.35 ± 3.76 vs. 33.61 ± 5.61 µkat·l -1 ; p < 0.05). No effects on the metabolism of nitrogen substances or minerals, insulin concentration in blood serum, and blood Cr concentration were observed. Chromium excretion in urine increased after parturition; higher concentrations were found in Cr-supplemented cows at p.p. weeks 3 (7.14 ± 1.72 vs. 5.00 ± 1.26 µg·l -1 ; p < 0.01) and 4 (8.40 ± 3.13 vs. 4.04 ± 1.32 µg·l -1 ; p < 0.01). Although chromium supplementation in the peripartal period significantly improved variables characterising the energy metabolism, no effects on milk yield for the first 100 days of lactation or on the incidence of clinical diseases were demonstrable.

The goal of the study was to use evaluation of blood and colostrum selenium (Se), copper (Cu) and zinc (Zn) concentrations of cows and the same blood concentrations of calves during the period of colostral nutrition to study differences in the metabolism of the different microelements in the mother and its young. Blood was collected from 12 cows and their calves before first intake of colostrum on the calving day and then at the end of the period of colostral nutrition to determine Se, Cu and Zn concentrations. First colostrum was collected from all cows. Se concentration was determined from whole blood and colostrum samples using hydride technique AAS. Cu and Zn concentrations were determined from colostrum and blood serum using flame AAS.The cows under examination were shown to have average concentrations of Se of 0.87 ± 0.30 and 0.47 ± 0.15 µmol·l -1 in whole blood and colostrum respectively, of Cu 8.95 ± 1.95 and 5.37 ± 1.80 µmol·l -1 in blood serum and colostrum respectively, and of Zn 11.62 ± 2.35 and 416.76 ± 120.07 µmol·l -1 in blood serum and colostrum respectively. Blood of calves before the first intake of colostrum was characterized by a significantly higher (p < 0.001) mean concentration of Zn (25.88 ± 8.79 µmol·l -1 ) and a significantly lower (p < 0.001) concentration of Cu (3.23 ± 1.08 µmol·l -1 ) compared with the mothers. Blood Se concentration of the calves (0.91 ± 0.26 µmol·l -1 ) was not significantly different from blood Se concentration of the cows. A significant increase (p < 0.001) in blood Cu concentration of the calves to 7.53 ± 1.98 µmol·l -1 and an insignificant increase in the mean Zn and Se concentrations to 26.40 ± 6.58 µmol·l -1 and 0.93 ± 0.32 µmol·l -1 respectively occurred during colostral nutrition. Correlation analysis showed a significant correlation (p < 0.01) between blood Se concentrations of the mothers and their newborn calves (r = 0.72). No significant correlation was found between Cu and Zn concentrations of cows and their calves. No significant relation between blood and colostrum concentrations of the different microelements of cows was found either.We have shown major differences as to the parameters of the micromineral metabolism under examination at the level of the mother/young relationship. While the calf organism can accumulate Zn throughout the intrauterine development and Zn is cumulated in cow colostrum, too, serum Cu concentrations of newborn calves are significantly lower compared with the mothers and colostrum Cu concentrations reach just about 60% of serum Cu concentrations of the cows. Although blood Cu concentration of calves increases throughout the period of colostral nutrition, it does not reach the level of serum Cu concentration of the mother by the end of the period. The Se status of newborn calves is similar to that of the mother cows and just like with Cu, Se is not cumulated in colostrum to any significant extent.

The aim of the study was to investigate the selenium metabolism in the maternal transfer of selenium to newborn calves. For a study, a total of 24 high-pregnant dairy cows at dry-off from two herds with different selenium status were used. While Herd I cows suffered from selenium deficiency, selenium status in cows of Herd II were adequate. Herd I cows were divided into three groups: E1, E2 and C. Selenium-and-vitamin supplement (Selevit inj. a.u.v.) was administered intramuscularly to cows of the E1 group 4 weeks before expected parturition, and the same supplement was administered to cows of the E2 group 8 and 4 weeks before expected parturition. The C group cows were controls, and received no supplement. On parturition days, samples of blood and of the first colostrum were collected from all of the cows. Blood samples were also collected from their newborn calves before they were given any colostrum. A statistically significantly higher selenium blood concentrations (p < 0.05) on parturition days were found in the E2 group cows compared with the control group (61.63 ± 8.23 µg·l -1 and 41.13 ± 11.08 µg·l -1 , respectively). Higher selenium blood concentrations were also found among cows in the E1 group. A similar trend was ascertained when a comparison between calves of groups E1 and E2 (63.96 ± 20.10 µg·l -1 and 66.86 ± 15.53 µg·l -1 ) and group C calves (51.98 ± 16.02 µg·l -1 ) was made. There was, however, no demonstrable difference in the glutathione peroxidase (GSH-Px) activity between groups from Herd I. Selenium concentrations in Herd II cows and their calves were 264.17 ± 48.71 µg·l -1 and 222.34 ± 52.95 µg·l -1 , respectively. Regression and correlation analyses demonstrated a statistically very close relationship (p < 0.01) between selenium blood concentrations of dams and their calves and blood GSH-Px activity of dams and their calves (y = 0.6489x + 28.049; r = 0.91, and y = 0.8033x + 91.169; r = 0.93, respectively). Because no significant correlation between blood and colostrum concentrations in cows was demonstrated (r = 0.21), colostrum should not be considered a suitable medium for the evaluation of selenium status in cows. The results showed the need to provide for a sufficient selenium saturation of dams also from the point of view of preventing selenium deficiency in calves.

Selenium status was assessed directly by determination of selenium concentration, or indirectly by measurement of glutathione peroxidase activity in whole blood samples collected from 879 cattle (733 cows, 63 calves, 42 heifers, 41 finishing bulls) reared on 93 farms in 12 of the 14 regions of the Czech Republic. Selenium deficiency or marginal values were found in 50 % of the tested animals and on 54 % of the farms. In terms of animal categories, deficient or marginal selenium status was found in 42 % of cows, 80 % of calves, 100 % of heifers, and 90 % of bulls. Seleniumdeficient herds were detected in almost all regions of the Czech Republic. The lowest selenium concentrations (< 20 µg . l -1 whole blood) were found in western, northern, and north-eastern Bohemia and in northern Moravia. It is evident that selenium deficiency in cattle is a topical problem in the Czech Republic and that selenium status must be monitored within preventive diagnostics in all age groups of cattle to decide correctly on the most effective way of supplementation.

The aim of the study was to optimize the method of blood and tissue selenium determination in ruminants, and to implement it in research and diagnostic practice. A method was developed for selenium determination by hydride generation atomic absorption spectrophotometry (HG-AAS) in full blood, blood plasma and serum, the liver, skeletal muscle tissue, the myocardium, and the kidneys after wet mineralization of samples in a closed nitric acid and hydrogen peroxide system and subsequent hydrogen chloride reduction. Hydride generation was performed by 1% sodium borohydride. The resulting selenium hydride was drawn off under inert atmosphere into a flameheated quartz T-tube to atomize; absorbance at 196 nm wavelength was measured by an optic system with deuterium lamp background correction. The measurements were verified by using diverse types of reference materials with declared selenium concentration and by a method of yield measurement of calibration solution addition in mineralized samples. The results corresponded with the stated values at the 95% probability level for all reference materials used. This methodology is acceptable as to both the detection limit (0.762 µg·l -1 ) and the error of measurement (4.6-15%) required for authorized use in research as well as clinical and preventive livestock medicine. The practical potential of the method was documented in a group of calves supplemented with two different forms of selenium.