Induction of Escherichia coli mastitis in cows fed selenium-deficient or selenium-supplemented diets

Abstract

SUMMARY Ten Holstein heifers were fed a selenium-deficient (SeD) diet (0.04 mg of Se/kg on a total ration dry-matter basis) 3 months before calving and throughout their first lactation. A selenium-supplemented (SeS) diet (2 mg of Se/head/d) was fed to a group of 10 heifers. In about the 14th week of lactation, the cows were challenge-exposed to Escherichia coli by administering 15 to 40 colony-forming units ( cfu ) into 1 mammary gland. Selenium concentration (μg/ml) in blood around the time of challenge exposure was 0.033 ± 0.002 (mean ± sem ) in SeD and 0.132 ± 0.006 in SeS cows. Infections were established in all challenge-exposed quarters. The frequency of quarter atrophy and agalactia, and reduction in whole-udder milk yield in the first 4 days after challenge exposure, were greater ( P < 0.05) in the SeD cows. Log 10 peak bacterial concentrations in milk were higher ( P < 0.05) in SeD (7.63 ± 0.34 cfu /ml) than in SeS cows (5.57 ± 0.66 cfu /ml). Mean log bacterial concentration was significantly higher ( P < 0.05) from 12 to 20 hours after challenge exposure in SeD than in SeS cows. Duration of infection was significantly greater ( P < 0.05) in SeD (162.0 ± 12.0) than in SeS cows (114.4 ± 18.0 hours). Milk somatic cell counts increased significantly more slowly ( P < 0.05) in SeD than in SeS cows from 8 to 16 hours after challenge exposure. Ratios of milk somatic cells to bacteria in milk were significantly lower ( P < 0.05) in SeD than in SeS cows at 12 and 16 hours after challenge exposure.