Cytoplasmic and mitochondrial genetic effects on economic traits in dairy cattle
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Maternal lineage effects on milk production 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 the Holstein-Friesian Herd Book, and 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 percent of phenotypic variation in 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. Ranges of maternal lineage estimates were 2934 kg milk, 154 kg fat, and.907 percent fat. Maternal lineage significantly affected fat percentage. Maternal 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 also affected calculated net energy of milk;Mitochondrial DNA (mtDNA) displacement-loop (D-loop) sequence polymorphism information from 36 maternal lineages was evaluated. Of 17 base pair substitutions evaluated, several were significantly associated with milk, fat, and solids-not-fat production. Another marked a large impact on fat percentage and net energy concentration. Positive and negative effects on all production traits were observed. One base pair substitution was related to a large favorable decrease in days open, number of breedings, and reproductive costs;Maternal lineage groups defined by several methods of classification using mtDNA sequence characteristics were evaluated with animal models. Groups defined as those maternal lineages with or without base pair substitution at nucleotide 169 accounted for increased milk fat and estimated milk energy production. Clustering the 36 maternal lineages using 17 mtDNA D-loop sequence differences produced groups with significant effect on fat percentage and energy concentration.