Association between days post-conception and lactation persistency in dairy cattle.

Area of Science:

• Dairy Science
• Animal Reproduction
• Lactation Physiology

Background:

• Optimal insemination timing is crucial for dairy cows, balancing pregnancy effects with milk production.
• Limited quantitative data exists on how lactation persistency changes during pregnancy relative to days in milk at conception (DIMc).

Purpose of the Study:

• To investigate the association between days post-conception (DPC) and lactation persistency.
• To determine how lactation persistency changes during pregnancy.
• To evaluate the influence of days in milk at conception (DIMc) on this relationship.

Main Methods:

• Analyzed milk production data from 23,908 cows across 87 herds in the Netherlands and Belgium (2005-2022).
• Measured lactation persistency using a lactation curve decay model, calculated at 8 stages of DPC (0-210 days).
• Utilized regression analysis with DPC, DIMc, parity, and their interactions as key variables.

Main Results:

• Lactation persistency decreased during pregnancy for both primiparous and multiparous cows.
• Multiparous cows showed a more significant decline in persistency between DPC 150 and 210 compared to primiparous cows.
• Conceiving later in lactation (higher DIMc) was associated with greater lactation persistency, though DIMc had minimal impact on persistency changes during gestation except for early DIMc groups.

Conclusions:

• Pregnancy negatively impacts lactation persistency, with distinct patterns based on DPC and parity.
• DIMc influences overall persistency levels but has a limited effect on the *rate* of change during gestation.
• Findings support improved reproduction management strategies by integrating lactation persistency insights.