Abstract: A sustained release capsule for introduction through the esophagus to the rumen of a ruminant has a tubular barrel containing a body of active composition urged by a piston and spring into sealing engagement with a constriction end wall shaped with a peripheral curved border leading to a frustoconical portion defining a delivery opening, the shape and width of such wall controlling the release rate to the rumen. The open front end of the barrel is closed by a hemispherical cap connected at the center of its convex outer face to a wing having opposite arms normally outstanding at near 90.degree. from the capsule body but resiliently bendable over a long arc along the convex face of the cap to retracted positions for introduction of the capsule through the esophagus. In the rumen, the arms return to near 90.degree. positions to hinder regurgitation of the capsule and to better withstand working and contractions of the rumen.

Abstract: Controlled release formulations comprised of a growth promoting agent admixed with a copolymer derived from lactic acid and glycolic acid and which is substantially free of polymerization catalyst are effective in the prolonged growth promotion of ruminants. A method for continuous dosing of active ingredients to a ruminant is provided.