Mesh-covered bolus

Claim 1

A rumen-retentive bolus comprising a medicament admixed in a bioerodible sustained-release matrix; a mesh made of a nonabsorbable material completely encasing said medicament-containing matrix; retention means to prevent the bolus from being regurgitated by the ruminant in less than two weeks which retention means is to have the medicament-containing matrix contain at least two matrix segments capable of changing their positions relative to each other after administration into the rumen, and wherein at least two of said matrix segments are joined together by flexible resilient means in the form of a coiled spring, so that the bolus segments can be formed into a shape suitable for administration from a bolling gun, and wherein dissolvable shape holding means are used to keep it in said shape until after it has been administered into the rumen and the shape holding means dissolved by the ruminal fluids, whereupon the bolus changes its shape to become sufficiently large that it cannot be regurgitated.