If a bull has no daughters, we rely totally on ancestry information. Once a bull has 75% reliability - about 33 daughters - it is eligible for inclusion in the Ranking of Active Sire (RAS) list. At this time, only about 16% of its BW is based on ancestry information with the rest based on the performance of its daughters in progeny test or commercial herds.
Sires with greater than 10,000 daughters have a reliability of approximately 99%, and BW or individual breeding values are based solely on the performance of their daughters in progeny test or commercial herds. The BW of a bull with no daughters is highly likely to change. The likelihood of an animals BW or individual breeding values changing reduce as more daughters are included in their bull proof.
LIC and CRV Ambreed include genomic information (as well as progeny test and commercial records) in their reliability estimate for bulls. So, a bull with no daughters but genomic information may have reliability greater than outlined above.
The reliability of individual cow BW and breeding values works in much the same way as for bulls. But, we cannot obtain 10,000+ daughters so reliability will never be as high for a cow as a widely used bull.
For cows, reliability depends on ancestry, own and progeny information. For a cow with no milk records, we rely totally on ancestry information (green line above) to determine reliability and how we weight the data. Once a cow has a milk record, a small proportion of its BW is based on her own records (orange line). Like a bull, progeny records (red line above) of a cow become progressively more important than her own or ancestry information.
For more detail: Description of Method to Estimate Reliability View PDF (47 kb)