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A Measure of Persistency of Lactation in Dairy Cattle¹

Dairy Husbandry Division, University of Minnesota

ABSTRACT

The variation in total milk production is influenced principally by three factors: 1) maximum initial production, 2) the persistency with which such yields are maintained, and 3) the length of the production period.

The importance of persistency in the economy of production has not been adequately investigated; however, sufficient evidence is available to justify the statement that, in general, cows having the highest degree of persistency are the most economical producers. Although several formulae for measuring persistency have been reported, none are entirely free from criticism. It is likely that no single formula can be so inclusive that it can apply equally well to all the different types or records that might be subjected to investigation. The formulae that have been reported may be classified into three groups. The first group includes the exponential curves which measure the rate of decline at any portion of the production period. The second group includes the regression coefficients which designate the slope of the lactation curve for only one portion of the period.

¹ Taken from data presented in a thesis submitted to the Graduate Faculty of the University of Minnesota by T. M. Ludwick in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Prepared with the assistance of Work Projects Administration, official Project No. 166-1-71-124, Sub-Project No. 447. Sponsor: University of Minnesota. Scientific Journal Series Paper No. 2036, Minnesota Agricultural Experiment Station.