Associations between postpartum phenotypes, cow factors, genetic traits, and reproductive performance in seasonal-calving, pasture-based lactating dairy cows

摘要

The objective of this study was to evaluate associationsbetween corpus luteum (CL) status, uterinehealth, body condition score (BCS), metabolic status,parity, genetic merit for fertility traits, and reproductiveperformance in pasture-based dairy cows managedfor seasonal reproduction. First- and second-lactation(n = 2,600) spring-calving dairy cows from 35 dairyfarms located in Ireland were enrolled in the study.Farms were visited every 2 wk, and animals that wereat wk 3 (range: 14–27 d in milk) and wk 7 (range: 42–55d in milk) postpartum were examined. Body conditionscore was measured using a 1-to-5 scale in 0.25-pointincrements. Transrectal ultrasound examination wasperformed at wk 3 and 7 postpartum to determinepresence or absence of CL and ultrasound reproductivetract score (scale of G1–G4). Blood samples werecollected at each visit, and the concentrations of glucose,β-hydroxybutyrate (BHB), and fatty acids (FA)were analyzed using enzymatic colorimetry. Animalswere grouped into 3 BCS categories [low (≤2.5), target(2.75–3.25), and high (≥3.5)], 2 CL categories (presentor absent), 2 uterine health status categories (normalor abnormal), and 3 metabolic status categories [good(high glucose, low FA and BHB), poor (low glucose,high FA and BHB), and moderate (all other combinations)].Fisher’s exact test was used to test for associationsbetween variables and was supplementedby logistic regression. More cows with a CL at wk 7were served during the first 21 d of the breeding periodcompared with cows without a CL. Cows classified ashaving a uterine score of G3 or G4 at wk 3 and 7had lower odds of pregnancy establishment during thebreeding period compared with animals with a uterinescore of G1 or G2. Animals with low BCS at wk 7had lower odds of pregnancy establishment than cowswith a target BCS. Cows classified as having goodmetabolic status at both wk 3 and wk 7 had greaterodds of pregnancy establishment during the first 21 dof the breeding season than those classified as havingpoor metabolic status. Overall, primiparous cows hadgreater reproductive performance than second-paritycows. Animals in the quartiles with the best predictedtransmitting ability for survival and calving intervalhad better reproductive performance compared withanimals in the other quartiles. Cows that had bettergenetic merit for fertility traits and good metabolicstatus, achieved target BCS, and had a favorable ultrasoundreproductive tract score and a CL present at wk7 postpartum had superior reproductive performance.