# Pilot Study: Exploring the Feasibility of Individual Voluntary Waiting Period Settings Using Postpartum Recovery Indicators in Dairy Cows

## TL;DR

This study explores using blood markers to determine individual recovery periods for dairy cows after calving, aiming to improve reproductive efficiency and farm productivity.

## Contribution

The study identifies specific blood markers that can objectively assess postpartum recovery in dairy cows for individualized voluntary waiting periods.

## Key findings

- Serum amyloid A and haptoglobin levels decreased during recovery, indicating their potential as inflammation markers.
- Total cholesterol and non-esterified fatty acids changed over time, reflecting metabolic recovery.
- Cortisol, substance P, and interleukin-6 showed no significant changes during recovery.

## Abstract

Following calving, dairy cows necessitate a sufficient recovery period before the next pregnancy because lactation and calving cause a negative energy balance and inflammation, respectively. This recovery period, known as the voluntary waiting period (VWP), has traditionally been set uniformly for all cows, although recovery rates differ by case. Here, we compared cows that recovered quickly after calving with those that recovered more slowly to identify blood markers reflecting recovery status. Blood parameters related to inflammation and energy metabolism were analyzed. The levels of two acute-phase proteins, serum amyloid A and haptoglobin, were high immediately after calving but decreased as recovery progressed, indicating their potential as markers of uterine and systemic recovery. Over time, total cholesterol increased, whereas beta-hydroxybutyrate and non-esterified fatty acids decreased, suggesting improved energy balance. Other stress and immune marker levels demonstrated no significant changes. Therefore, blood analysis can provide an objective method for evaluating postpartum recovery instead of relying solely on clinical or subjective assessments. Establishing individualized VWPs based on physiological recovery may reduce unnecessary waiting periods, improve conception rates, and enhance overall farm productivity.

This study aimed to identify hematological markers that can objectively assess postpartum recovery in dairy cows, which is essential for determining an individualized voluntary waiting period (VWP). Twenty Holstein cows were divided into early recovery and late recovery groups based on their clinical uterine recovery. Blood samples were collected from coccygeal vessels and analyzed for inflammatory and metabolic markers, including serum amyloid A (SAA), haptoglobin (HPT), cortisol (COR), substance P (SP), interleukin-6 (IL-6), total cholesterol (T-Chol), beta-hydroxybutyrate, and non-esterified fatty acids (NEFA). Both SAA and HPT significantly decreased after recovery compared to immediately after parturition (p < 0.001), whereas T-Chol and NEFA significantly increased and decreased over time, respectively, indicating recovery from a negative energy balance status. No significant changes were observed in COR, SP, or IL-6 levels. Thus, SAA and HPT are sensitive indicators of postpartum inflammation, whereas T-Chol and NEFA levels reflect metabolic recovery. Using these hematological markers enables a more objective and customized setting of VWP for each cow, potentially improving reproductive efficiency and farm profitability. Further studies are warranted to establish cutoff values for each parity and validate the applicability of individualized VWP models.