Trend in dairy sheep BLG genotype found with repeatability test-day model.

A total of 19.207 test-days, collected on 4 farms from 1999-2006 and belonging to 1109 Valle del Belice dairy sheep were analyzed with a repeatability model. After strict outlier analysis 17.747 records were retained. Animals were reared in an extensive system resulting in large environmental influences. However, significant genetic variation was detected in production traits (milk production mean=1336 stdg=93 g/d, fat+protein 167 stdg=12 g/d). Heritability was only 3% while the interaction year by month of test-day explained 27% of the variation. A protein and DNA analysis program was initiated in order to facilitate selection to maintain these flocks under these conditions. In total 427 animals were typed for the -lactoglobulin locus. Using the recorded pedigree this genotype information was spread over the entire population. The trend in frequency for the AA genotype was significantly negative (p-value=.0057), as were trends in milk yield and lactation length. Possibly farmers have a preference for the BB animals. Relations with production traits were indicative for this trend, but not significant. A possible explanation is the relevant, but non significant difference in length of the lactation between AA and BB animals.