Identification of culling reasons, intervals, and risk factors by postpartum period classification in dairy farms.

Objective: This study aimed to identify the reasons, intervals, and risk factors in Korean dairy farms where cows produce large volumes of milk under challenging conditions.

Methods: A total of 11,361 calving datasets were analyzed to determine culling reasons and intervals, and the factors affecting culling risk. The postpartum period was classified into three categories: within 60 days (Period 1), between 61 and 210 days (Period 2), and beyond 210 days (Period 3) postpartum.

Results: The culling rates were 7.4% in Period 1, 8.5% in Period 2, and 11.3% in Period 3, totaling 27.2%. The main reasons for culling were infertility, mastitis, voluntary causes, peripartum disorders, and other health problems. Culling due to infertility (333 days), mastitis (142 days), or other health problems (129 days) was associated with longer median calving-to-culling intervals, whereas culling due to peripartum disorders (19 days) had shorter intervals compared to voluntary culling (101 days, p < 0.0001). Cows with a higher body condition score (BCS) (≥3.75) at dry-off were more likely to be culled in Period 1 (odds ratio [OR]: 1.83, p < 0.0001) than those with a BCS of 3.5. In period 1, cows with a BCS increase between dry-off and calving had a lower likelihood of culling (OR: 0.65) than cows with no BCS change, while those with a BCS decrease had a higher likelihood of culling (OR: 1.29) in Period 2 (p < 0.05). Cows with peripartum disorders were more likely to be culled throughout all periods (p < 0.01) than cows without disorders. The probability of culling increased (p < 0.0001) with higher parity across all periods.

Conclusion: Preventing high BCS at dry-off and BCS reduction during the dry period, minimizing the incidence of peripartum disorders and other health problems, and improving reproductive efficiency can help reduce involuntary culling.