Researchers have constructed a force transducer to study the forces exerted by the liner on the teat during milking. The objective was to develop a method of comparing the action of different liners under a variety of different milking conditions… They have published on the ‘touch-point pressure ‘of liners and the ‘compressive load applied across the teat. Consistent finding is that the forces applied to the teat tip are several times greater than those applied to the sides of the teat barrel. This difference in force is intentional. When a liner closes around the teat during the D phase and some latest research commenting on the C phase of the pulsation cycle, the purpose is to squeeze the teat from the tip such that the waste fluids of tissue metabolism can pass back into the normal circulatory system of the udder. The increased pressure applied to the curved teat end is a result of the tension along the liner length that results from it being stretched within the shell assembly. The degree of stretch and the way in which the liner delivers its force to the teat end depends on the teat shape and the characteristics of the liner and shell. Since there is little that can be done about the variety of teat end shapes within the herd, changes can be made in the degree of callosity or hyperkeratosis by using different liner and shell combinations
Some teat end lesions may be explained by observations that the liner collapses in a fixed plane, and liner pressure can vary with lateral teat position and depth of teat penetration.
Dry split and Calloused teat ends provide a better environment for bacterial survival outside the cow and any multiplication of bacteria will occur in extremely close proximity to the teat orifice. It is perhaps not without reason to suppose that a heavily calloused teat end may also behave differently once infection is forced up the teat orifice and into the udder. In other words, what can be seen outside the teat may imply changes within the teat that are also associated with an increased risk of new infection.