Summary The dairy cows at the Estonian Agricultural University appeared to have an extremely low selenium status. The selenium level was 5.6 μg/l in whole blood and 3.2 μg/l in milk, on average. The blood glutathione peroxidase was consequently extremely low. The effects of organic selenium (selenized yeast) and sodium selenite were compared in a feeding experiment on 100 dairy cows. Selenium incorporation, udder health and the in vitro function of blood neutrophils were monitored. Supplementation of the feed either with 0.2 ppm organic selenium or sodium selenite for 8 weeks, increased the blood selenium level (geometric mean) within this period from the background level (about 5.6 μg/l) to 167 (Se‐yeast) and to 91 μg/l (selenite). The respective change in whole blood glutathione peroxidase (GSH‐PX) was from 0.22 to 3.0 (Se‐yeast) and to 2.3 (selenite) μKat/g Hb. Blood GSH‐PX continued to increase up to 10 weeks after the supplementation was stopped. The bioavailability of yeast selenium was superior to selenite: the relative bioavailability (selenite = 1) of yeast selenium was 1.4 if blood GSH‐PX, 1.9 if blood selenium, and 2.7 if milk selenium was used as the response criterion. Selenium‐supplementation showed a positive effect on udder health. The percentage of quarters harbouring mastitis pathogens dropped from 22.9 to 13.0 in the Se‐yeast group and from 18.4 to 7.4 in the selenite group during the supplementation period. The effect of selenium on mastitis was also reflected as a decrease in the output of milk somatic cells and N‐acetyl‐β‐D‐glucosaminidase (NAGase). The time‐luminescence profile of zymosan‐induced activity of blood neutrophils became skewed to the left in Se‐supplemented cows.

Enrofloxacin (Bayad@) was injected into arteries supplying the udder of dairy cows. The idea was to avoid primary dismbution, metabolism and elimination and thus to deliver the drug to the target organ at hgha concentration. Enrofloxacin injected into the abdominal aorta or the external iliac artery resulted in high initial enrofloxacin retention by the udder and high milk concentrations.Injection of enrofloxacin into the abdominal aorta resulted in 2.2 times higher milk peak concentration of the drug than intravenous injection into the jugular vein. Injection of the drug into one of the two external iliac arteries dowed dmg concentrations of milk from the udder halves to be compared: when enrofloxacin w a s injected into the right external iliac artery, the peak milk enrofloxacin concentration from the right udder half was 4.8 times that of the left udder half. The bulk of enrofloxacin was absorbed from the milk compartment of the udder before the next regular milking 6.5 h later. By this time, the metabolite cipmfloxacin had accumulated in milk. Pharmacokinetic values for enrofloxacin and its metabolite ciprofloxacin are given separately for serum and milk whey following thrcc intravascular dosing mutes SANDHOLM, 1995). Drug concentrations in milk are low for many oral and parented antibacterial preparations. The drug can be targeted into a selected organ by injecting the dose into the artery supplying blood to that organ. Intra-arterial injections into cows have been a common practice in the former east block countries: Estonia, East Germany and Russia. The intra-arterial route of administration is rarely used in Western type veterinary practice. Although there have been a few reports on the clinical efficacy of antibacterials administered by the intra-arterial route in mastitis and metritis (LIPOV~SEV, 1964; COLOMBO land GUALLINI, 1967; MA= et al., 1987, sound pharmacokinetic studies are laclung. The us. CoplmBht acents S~D~~C 0931-184X/96/4306-0377$11.50/0

Previous investigations have shown that selenium supplementation inhibits growth of mastitis pathogens in cow's milk. The present study was performed to clarify the role of selenium in defence mechanisms of mammary gland. We have examined the effects of selenium supplementation on Staphylococcus aureus growth inhibiting activity in whey. Six selenium-supplemented and six non-supplemented Estonian dairy cows were used for this study. Selenium-supplemented cows received 4 mg organic selenium in the form of selenium yeast in their daily diet for 8-week period. Cows from non-supplemented group received the same amount of yeast free of selenium in their diet. All cows had initially low blood glutathione peroxidase (GPx) activity (

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