Fixed yield responses to increased milking frequency.

Data from 19 literature reports that measured the effect of milking frequency on milk yield were summarized. When milking three times daily was compared with milking twice daily, the three times daily yield was 3.5 kg/d higher with a 95% confidence interval of 3.1 to 3.9 kg/d. Response of fat yield to increased milking frequency, from twice daily to three times daily, was 92 g/d, and the 95% confidence interval was 67 to 117 g/d. Linear regression analysis showed that no relationship existed between twice daily milk yield or fat yield and the amount of increase of milk yield or fat yield caused by increasing milking frequency to three times daily. This result implied that increased milking frequency from twice to three times daily resulted in a fixed increase of 3.5 kg/d of milk yield and 92 g/d of fat yield, regardless of the yield for cows milked twice daily. Responses of primiparous and multiparous cows were similar in magnitude for twice daily versus three times daily milking frequency, suggesting that the separate adjustment factors currently used for conversion of three times to twice daily equivalents for primiparous and multiparous cows may not be needed if adjustments are expressed on the basis of actual yield. The numbers of comparisons of once daily and four times daily milking frequency with twice daily milking were limited, but showed no relationship with milk yield, and the mean response was -6.2 and 4.9 kg/d, respectively. These data also support the concept of a fixed yield response to altered milking frequency.(ABSTRACT TRUNCATED AT 250 WORDS)