Relationships between polymorphism for mitochondrial deoxyribonucleic acid and yield traits of Holstein cows

Two independent data files from the breeding herd of Iowa State University and six North Carolina herds were used to examine relationships between yield traits and mtDNA polymorphism. Maternal lineages were established by tracing ancestry of cows to founder females in the herd book of the Holstein Association. Data from Iowa State University were 1476 records from 602 cows from 29 maternal lineages. The nucleotides of mtDNA encoding rRNA were sequenced. Eleven sites of polymorphism were found. An animal model for gene substitution was used to examine the relationship between sequence differences and yield traits. Traits analyzed were mature equivalent yield of milk, fat, SNF, and milk energy as well as concentrations of fat, SNF, and milk energy. Effects of sequence differences were significant for most traits. Sequence information from the D-loop was available for 12 lineages from North Carolina. The effect of polymorphism at 4 sites was examined using 1472 records from 668 cows. Traits measured were the same, except that protein replaced SNF. No significant relationships existed between any of the traits and D-loop polymorphism, but results suggested that an association might exist between polymorphism and concentrations of milk yield, fat percentage, and energy. Whenever a significant relationship was detected, the effect of mutation (rare genotype) was detrimental.