Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/22/2003
Publication Date: N/A
Technical Abstract: National genetic evaluations of daughter pregnancy rate are based on data from 40 million lactation records of 16 million cows that calved since 1960. Up to five lactations are included per cow. Date pregnant is determined from several data sources. The most accurate information is last insemination date verified by birth date of next calf within 15 d of expected birth date. For lactations with no reported inseminations, date pregnant is obtained by subtracting mean gestation length (280 d for Holsteins) from next calving date. For lactations without next calving date, date pregnant is assumed to be the last insemination date unless the cow was subsequently examined and verified not pregnant, or was still milking in the same lactation more than 295 d after the last insemination. Last reported breeding date is used if the next lactation is initiated by abortion. A final data source is an owner report that the cow was sold because of infertility. Such cows are assumed to be nonpregnant and the last insemination date is disregarded. Records for pregnancy rate are considered to be complete at 250 d in milk (DIM), and pregnancy status after 250 DIM is not used. Date pregnant is set equal to 50 DIM for cows that become pregnant before 50 DIM. Some early pregnancy dates calculated from next calving date are inaccurate because of short gestations or unreported abortions. Therefore, lower and upper limits of 50 and 250 DIM, respectively, were applied after adjusting days open for season effects; 5 and 14% of records were affected. For Holstein calvings during 1998 and 1999, 57% had breeding date verified by calving date; 6% had next calf born with no previously reported breeding date; 5% had breeding date inconsistent with birth date of next calf; and 5% had the cow reported as sold for reproductive reasons. Although accurate breeding dates are reported by most farms, 19% of reported final breeding dates could not be verified because the cow was sold for reasons other than fertility.