5 A SINGLE NUCLEOTIDE POLYMORPHISM IN COQ9 AFFECTS MITOCHONDRIAL FUNCTION, BODY WEIGHT CHANGE AFTER CALVING, AND FERTILITY IN HOLSTEIN COWS

A single nucleotide polymorphism for COQ9 has been associated with genetic merit for fertility in 2 separate populations of Holstein cattle, with the A allele associated with higher fertility. COQ9 is necessary for the synthesis of coenzyme Q10, a component of the electron transport system of the mitochondria. We evaluated the effect of COQ9 genotype on the electron transport system, body weight changes after calving, and phenotypic measurements of fertility and production in Holstein cows. The single nucleotide polymorphism in COQ9 was genotyped using a Sequenom MassARRAY® (Sequenom Inc., San Diego, CA, USA). In the first study, cows ≥200 days in milk were selected for analysis of mitochondrial oxygen consumption [COQ9 genotype: AA (n = 12), AG (n = 12), and GG (n = 12)]. Peripheral blood mononuclear cells were isolated and respiration assessed using the Oroboros O2k high-resolution respirometer to evaluate routine respiration, R; leak respiration, L; and electron transport system capacity, E. There were additive effects of genotype on respiratory function (P < 0.05): R was 3.4 ± 0.3, 4.7 ± 0.3, and 4.9 ± 0.3 pmol of O2/s per 106 cells, L was 1.9 ± 0.3, 2.7 ± 0.3, and 3.0 ± 0.3 pmol of O2/s per 106 cells, and the uncoupling control ratio (E/R) was 3.4 ± 0.2, 2.5 ± 0.2, and 2.1 ± 0.2 for AA, AG, and GG, respectively. In a second study, body weight was recorded for AA (n = 106), AG (n = 223), and GG (n = 86) cows during the first 20 weeks postpartum for 2 consecutive lactations. In both lactations, body weight postpartum was affected by genotype × time postpartum (P < 0.001), with cows of the AA genotype experiencing less weight loss than AG (second lactation only) and GG cows. Days open, services per conception, and 305-day milk yield (MY) for the first 2 lactations were evaluated in a population of 2273 Holstein cows grouped based on predicted transmitting ability for daughter pregnancy rate: ≤–1 (n = 1220) and ≥1.5 (n = 1053). Continuous data were analysed using the MIXED procedure of SAS, and categorical data were analysed using the GLIMMIX procedure. The model included farm, genotype, and the numerator relationship matrix to account for (co)variances among animals. Additive and dominance effects were estimated. Genotype affected each trait (P < 0.05). Values for AA, AG, and GG for the first lactation were as follows: days open, 123.6 ± 3.5, 134.3 ± 2.8, and 139.4 ± 3.5 days; services per conception, 2.4 ± 0.1, 2.5 ± 0.1, and 2.7 ± 0.1; and MY, 11 278 ± 65, 11 416 ± 51, and 11 478 ± 65 kg. For the second lactation COQ9 affected (P < 0.05) days open (133.2 ± 4.7, 142.9 ± 3.1, and 147.9 ± 3.9 days) and services per conception (2.5 ± 0.1, 2.6 ± 0.8, and 2.7 ± 0.1), but there was no effect (P = 0.63) on MY (11 486 ± 66, 11 502 ± 52, and 11 526 ± 57 kg). Results indicate that the same genotype associated with genetic merit for fertility (AA) is associated with more efficient respiratory function and less body-weight loss postpartum. Moreover, the favourable genotype was associated with higher phenotypic measurements of fertility and lower MY. Results indicate the single nucleotide polymorphism in COQ9 could be a potential marker for fertility and that allelic variants may affect fertility by altering respiratory efficiency. Study was supported by USDA AFRI 2013–68004–20365.