The pathogenicity of some ovine or caprine mycoplasmas in the lactating mammary gland of sheep and goats

Abstract

Mycoplasma ovipneumoniae, M. arginini and M. conjunctivae were each inoculated into the lactating mammary gland of goats and sheep. M. ovipneumoniae was mastitogenic in both species, causing persistent colonization, raised lacteal cell numbers, decreased milk output and separation of milk into 3 layers throughout the periods of observation in virtually all animals. Its effects in sheep were variable, however, and appeared to depend less on the strain and titre of inoculum than on individual variation in response. M. arginini and M. conjunctivae were not mastitogenic for goats, but one of each pair of sheep injected with these agents showed organism persistence at high titres and lacteal neutrophilia over 9 days of observation. Effects on milk production were obscured by the apparent poor ability of the ovine udder to regain previous yield after a fall in output, but milk consistency and appearance were only temporarily or mildly affected in these animals. A. laidlawii, injected into sheep only, produced transient effects but with poor recovery of milk production after elimination of the organism. Goats were superior to sheep in consistency of reaction and milk output, and equally if not more susceptible to intra-mammary challenge with M. ovipneumoniae. The goat was therefore concluded to be the better experimental animal in a potentially useful method for screening strains of M. ovipneumoniae for virulence.