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Abstract
The early New Zealand dairy industry developed under conditions of machine milking followed by hand stripping, a practice which may have influenced the requirements of cows for stimulation before milk ejection, and the milk ejection response to machine milking. The studies reported here show that adequate milk ejection can be achieved by the application of a pre-milking stimulus, a practice which was not necessary in later years. The milkfat yield response to this stimulus decreased with succeeding generations from 33% in 1958 to zero in 1978 in a series of studies using monozygotic twin cows of mainly Jersey breed. The response to stimulus was greatest in low-producing cows. Studies over three years using a herd of 80 cows showed no effect of age on stimulus requirement. A survey of 560 industry cows showed that the distribution of sire group mean stimulus requirement was bimodal with means 9±2 s and 29±6 s.