In-line milk progesterone monitoring as a tool for precision reproductive management

In-line milk progesterone (IMP4) monitoring (Herd Navigator, DeLaval) is a technology that automatically detects onset of cyclicity, estrus, and pregnancy. Sampling starts at 20 DIM and occurs on average every 2 d until pregnancy. Estrus is detected based on a decline in progesterone (P4) concentrations below a threshold, and pregnancy is assessed from 30 to 55 d after AI in cows without return to estrus. Here, we review the potential of IMP4 as a tool for reproductive management. In a series of observational studies with up to 158,961 IMP4 records from 4,353 AI events, we characterized predictors of pregnancy per AI (P/AI) and investigated IMP4 profiles in cows returning to estrus. Some of the predictors included prolonged luteal phase before AI and suboptimal P4 levels at different time points before and after AI. Over one-third of cows had at least one characteristic of P4 profile unfavorable to P/AI, but with low predictive abilities. Among nonpregnant cows, 5% returned to estrus by 17 d after AI, 64% between 18 and 24 d, 16% between 25 and 30 d, and 15% between 31 and 55 d. This represents 85% of cows that are not pregnant 55 d after AI returning to estrus before 30 d, when first pregnancy diagnosis occurs in many dairies. Monitoring IMP4 might be used to identify subgroups of cows with different predicted P/AI to develop selective breeding strategies or targeted interventions. It can also aid in identifying nonpregnant cows early for timely reinsemination.