Influence of density and location on degradation of sustained-release boluses given to cattle.

To better understand the factors involved in erosion of sustained-release ruminal boluses, studies were conducted to determine the relationship between density of the bolus and location in the forestomachs and the influence of these factors on bolus erosion. Boluses with densities of 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.4 g/cm3 were produced from inert materials and administered to 6 fistulated Hereford heifers. A minimum density of 1.6 g/cm3 was required to prevent regurgitation from the ruminoreticulum and a minimum of 2.0 g/cm3 for retention in the reticulum. Release of oxytetracycline from 2 boluses placed in the reticulum or in the rumen was measured in 12 fistulated Hereford heifers. Boluses retained in the reticulum had higher rates of release (P less than 0.05) than those in the rumen. The smaller reticular compartment apparently caused greater contact between individual boluses and resulted in more rapid erosion.