Plasma progesterone concentration after first service is associated with individual genetic traits, postpartum phenotypes, and likelihood of conception in seasonal-calving pasture-based dairy cows

摘要

The aims of this study were to (1) evaluate postpartumphenotypes, cow factors, and genetic traits associatedwith plasma progesterone (P4) concentrationsafter first artificial insemination (AI); (2) determinevariation in daily plasma P4 concentrations betweend 7 and 13 after first AI; and (3) evaluate associationsbetween plasma P4 concentrations and pregnancy successafter first AI. First and second parity (n = 2,797)spring-calving lactating dairy cows from 35 dairy herdswere enrolled. Farm visits were performed every 2 wkduring the postpartum period as follows: cows thatwere at wk 3 (range: 14–27 d in milk) and wk 7 (range:42–55 d in milk) postpartum were examined. Farm visitswere performed weekly during the breeding season,and cows that were between 7 and 13 d after the firstAI were examined. Body condition score (BCS) wasmeasured at each visit using a 1 to 5 scale [low (≤2.75),target (≥3.0)]. Transrectal ultrasound examinationswere conducted at wk 3 and wk 7 postpartum visits todetermine presence or absence of a corpus luteum (CL)and uterine tract score [scale of G_1 (best)–G_4 (worst)].Blood samples were collected at each visit, and plasmaconcentrations of glucose, β-hydroxybutyrate, and fattyacids were analyzed. On the day of the weekly farmvisit during the breeding season, blood samples for P4determination were collected from all cows that werebetween 7 and 13 d after first AI during the breedingperiod. Cows that had a CL present and a G_1 uterinescore at wk 7 postpartum had greater plasma P4 concentrationafter first AI (+0.67 ng/mL and +0.4 ng/mL, respectively) compared with cows with no CL presentand with a uterine score ≥G_3. Cows with low BCSat wk 7 postpartum had lesser plasma P4 concentrationafter first AI than cows with target BCS. Each unitincrease in plasma fatty acids and β-hydroxybutyrateconcentration at AI was associated with 0.45 ± 0.33ng/mL (estimate ± standard error) and 0.07 ± 0.04ng/mL greater plasma P4 concentration after first AI,respectively. Regarding genetic merit traits, each unitincrease in fertility subindex was associated with 0.005± 0.003 ng/mL greater P4 concentration. In addition,for every 1 ng/mL increase in plasma P4 concentration,the odds of estimated probability of pregnancy per AIincreased by 3% (odds ratio = 1.03; 95% confidenceinterval = 1.00, 1.05). In conclusion, cows with superiorgenetic merit for fertility traits and milk productiontraits, favorable fertility phenotypes at wk 7 postpartum,(e.g., presence of a CL, a G_1 uterine score, andtarget BCS), and blood parameters indicative of bettermetabolic status at AI were all associated with greaterplasma P4 concentration after AI. In turn, greaterplasma P4 concentrations were associated with greaterodds of successful pregnancy establishment. This studyunderlines the important associations between earlypostpartum fertility phenotypes (CL presence, uterinehealth status) and subsequent plasma P4 concentrationsafter first AI, and hence provides additional evidenceof the mechanisms through which selection for fertilitytraits improves phenotypic fertility performance.