Effects of physical characteristics of milking machines on teats and udders.

A milking machine must remove milk from a cow thoroughly and rapidly but not impose excessive stress or contaminate teats with bacteria. The machine removes milk by applying vacuum to the exterior of the teat until it stretches sufficiently to open the streak canal. Periodic collapse of the teat cup liner relieves tension on the teat sphincter and aids circulation of blood through the teat. The milking machine may affect the likelihood of mastitis by directly implanting pathogenic organisms into the streak canal, by engendering long-term deterioration of the teats, and by serving as a reservoir of pathogens.