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Walford Transformation of Returns to Service as a Measure of Breeding Efficiency

Department of Dairy Science, University of Illinois, Urbana

ABSTRACT

It has become common to express breeding efficiency in terms of percentage of cows not returning to service in the period 30–60 days (or 60–90 days) following service. It is known that these estimates are higher than actual calving percentages, but the latter are not readily available and are obtained too late for current management decisions. It would be useful if more precise estimates of calving percentages could be derived from the early return to service data.

In examining return to service data obtained from the Central Ohio Breeding Association (COBA), it occurred to us that returns to service might follow the form of growth curves with constant percentage decreases in increments with time, approaching as asymptotes the actual number of cows failing to calve to service. The complements of such curves (nonreturn to service curves) are shown by Erb and Flerchinger (2) up to the 180th day for services to semen of bulls of different levels of fertility and with different antibiotics as additives to the semen.