Effects of cow families on production traits in dairy cattle

The components of phenotypic variance attributable to maternal lineage for production traits of the UK Holstein Friesian dairy population were estimat ed. First lactation production records of 55 230 cows calving between 1996- 1998 in the UK Holstein Friesian population were used in the analysis. Mate rnal pedigree records were traced back to 1960 to establish maternal lineag es. The tracing resulted in 36 320 cows being assigned to 11 786 cow famili es with more than one cow per maternal lineage. Using test day records it w as possible to explore aspects of the lactation curve in terms of persisten cy and different periods of production. The traits analysed were 305-day mi lk yield and composition traits, the first three milk yield tests of lactat ion and two measures of persistency. A contemporary record design was used to minimize pair-wise additive direct genetic relationships between cows wi thin a maternal lineage and to remove both the effect of heterogeneous vari ance over time and the complications of permanent environment effects. No s ignificant component of variance attributable to maternal lineage was found for yield traits. When data were restricted to maternal lineages with five or move records, persistency, as a untie of cumulative yield in the last t hird to that in the first third of a 300-day lactation, was estimated to ha ve a 4.4% component due to maternal lineage variance significant at the 5% level. The study also investigated the preferential treatment of cow famili es. Some evidence of maternal lineage X herd interaction was found.