THE IMPORTANCE OF MATERNAL LINEAGE ON MILK-YIELD TRAITS OF DAIRY-CATTLE

Maternal lineage effects on milk yield traits, considered indicative of cytoplasmic inheritance, were evaluated with animal models. Cattle were from a selection experiment begun in 1968. Maternal pedigrees were traced to the first female member in die Holstein-Friesian Herdbook, purchased cows entering the herd, considered foundation females, were assigned to maternal lineage groups. All models accounted for year-season of calving, parity, and selection lines. Maternal lineage effects were included in a repeated records model with cow effects and preadjustment for sire and maternal grandsire transmitting abilities. Maternal lineage accounted for 5.2, 4.1, and 10.5% of phenotypic variation of preadjusted records of milk yield, fat yield, and fat percentage, respectively. Maternal lineage was evaluated as a fixed effect in an animal model including random animal and permanent environmental effects. Matemal lineage significantly affected fat percentage but not milk yield. Matemal genetic (nuclear) effects and their covariance with additive animal effects did not significantly account for additional variation nor did they influence maternal lineage estimates. Maternal lineage affected calculated net energy of milk but was not important for SNF yield or concentration. Matemal lineage influenced fat percentage, energy concentration, and, to a lesser extent, fat yield in milk of dairy cattle.