Teat thickness changes may provide biological test for effective pulsation.

Abstract

Pulsation rates of 40, 60 and 80 cycles/min were combined with pulsator ratios of 50, 60, 70 or 80 percent in two experiments with different liners. Machine-induced, short-term changes in teat thickness of 14 cows were compared with milk flow rate characteristics and machine strip yields to evaluate the effectiveness of pulsation in relation to liner type. Post-milking teat thickness increased progressively as the b phase of the pulsation cycle was lengthened, and as the d phase was shortened, at all pulsator rates and with either liner. Teat thickness values increased significantly (P < 005) when the d phase was < 15%. For ratios of 50 and 60% , teat thickness decreased progressively as pulsation rate was increased. At the higher ratios, thickness values were lowest at 60 cycles/min. Pulsation settings that tended to increase teat thickness values also increased both peak milk flow rates and machine strip yields. The influence of liner type on teat thickness changes appeared to be at least as important as the influence of pulsator ratios and greater than the effect of pulsation rate. If so, then international standards for acceptable pulsation characteristics cannot be defined solely in terms of pulsator settings. A limit of +/- 5 percent for machine-induced changes in thickness of the teat apex would be an additional guideline for effectiveness of pulsation in relation to both liner type and vacuum level. This could provide a basis for a dynamic test applied to milking cows under field conditions.