Use of early lactation days open records for genetic evaluation of cow fertility.

National genetic evaluations for cow fertility were introduced by the USDA in February, 2003. These evaluations, reported as daughter pregnancy rate, are based on days open. One requirement of the evaluation system is that lactations be at least 250 d in milk (DIM) to be included for analysis. The objective of this research was to develop a predictor of days open, usable in genetic evaluation, to allow for earlier predicted transmitting abilities (PTA), especially for young bulls. The final prediction equation included an overall intercept, the effects of lactation and calving ease score, the linear and quadratic effects of age at calving, and a regression on days open based on last breeding. Data used for estimation were breeding records from 4 dairy records processing centers for the years 1995 through 1998. Genetic correlations were > or =0.91 by d 130, and phenotypic means of predicted days open were in agreement with means for final days open, indicating that the predictions were phenotypically unbiased. Comparison of mean PTA based on actual and predicted days open indicated no bias in PTA, and correlations between PTA were > or =0.92 by d 130. The earlier use of data increased reliability by about 5% for sires between the ages of 4 and 5 yr. The USDA began using predicted days open for records that are at least 130 DIM in national evaluations starting November, 2003.