SUSTAINED-RELEASE BOLUSES TO SUPPLY TRACE-ELEMENTS AND VITAMINS TO CALVES

Cylindrical rumen boluses of a size (55 mm length x 18 mm diameter, de nsity 2.9 g cm(-3)) appropriate for ruminating calves over 75 kg livew eight were constructed. The mean daily nutrient releases from two rume n boluses measured in rumen-cannulated cows were 62 mg Cu, 0.56 mg Se, 1.08 mg Co, 1.14 mg I, 38 mg Mn and 55 mg Zn with vitamins 3140 IU A, 628 IU D-3 and 9 IU E. In a 123-day experiment with housed dairy calv es given hay and a barley/soyabean meal mix, administration of two rum en boluses significantly increased plasma copper and blood glutathione peroxidase levels compared with unsupplemented control calves. There were similarly significant responses in a 143-day experiment with suck led beef-cross calves treated with two rumen boluses at grass. In both circumstances the basic diets provided inadequate allowances of both copper and selenium.