Postpartum vaginal discharge score is associated with genetic traits, postpartum fertility phenotypes, metabolic status, and overall reproductive performance in seasonal-calving pasture-based dairy cows.

The aims of this study were (1) to evaluate potential associations between genetic traits, postpartum phenotypes, cow factors, and postpartum vaginal discharge score (VDS); and (2) to investigate possible associations between postpartum VDS, plasma progesterone (P4) after first service, and reproductive performance. First- and second-parity (n = 2,842) spring-calving lactating dairy cows from 35 dairy herds were enrolled. Farm visits were performed every 2 wk during the postpartum period and weekly during the breeding period. Cows that were at wk 3 and wk 7 postpartum and between 7 and 13 d after first artificial insemination (AI) were examined. Body condition score (BCS) was measured on all farm visits using a 1-to-5 scale (low ≤2.5; target ≥2.75). Transrectal ultrasound examinations were conducted to determine the presence or absence of a corpus luteum (CL). Vaginal discharge score was determined at wk 3 and wk 7 using a Metricheck device (Simcro) and a 1-to-4 scale (1 = clear mucus; 4 = mucopurulent with >50% purulent material ± odor). At wk 3, cows having a VDS ≤2 were considered to have normal reproductive tract health status (RTHS). At wk 7, cows having VDS = 1 were considered to have normal RTHS. Blood samples were collected at each visit, and plasma concentrations of glucose, β-hydroxybutyrate, fatty acids, and progesterone (only during breeding visit) were analyzed. Animals with target BCS at wk 3 and wk 7 had greater odds of having normal RTHS at wk 3 and wk 7, respectively, than cows with low BCS. Cows with a CL at wk 3 and wk 7 had greater prevalence of normal RTHS at wk 3 and wk 7, respectively, compared with cows without a CL. Cows with normal RTHS had a lesser plasma concentration of β-hydroxybutyrate at wk 3 and wk 7 and greater plasma concentration of glucose at wk 3 compared with animals with abnormal RTHS. More cows in the greatest quartiles for the fertility subindex of the Economic Breeding Index and genetic merit for milk production traits (milk kg and milk protein [%]) had normal RTHS at wk 3 and wk 7 compared with the other quartiles. Cows with VDS = 4 at wk 7 postpartum had lesser plasma P4 concentration after first AI (-1.2, -1.1, and -1.0 ng/mL compared with cows with VDS = 1, 2, and 3, respectively). Similarly, cows with VDS = 4 at both wk 3 and wk 7 had lesser pregnancy at first service, lesser cumulative pregnancy rates at wk 3, 6, and 12 during the breeding period, and longer interval from mating start date to conception (+3 d if VDS = 4 at wk 3; +5 d if VDS = 4 at wk 7), compared with cows having other VDS. In conclusion, cows with superior genetic merit for fertility traits and milk production traits, and favorable fertility phenotypes at wk 3 and wk 7, were all associated with greater likelihood of having normal RTHS. In turn, abnormal postpartum RTHS and greater postpartum VDS (score = 4) were associated with lesser odds of successful pregnancy establishment.