Relationship Between Milk Fatty Acid Profile and Fertility at Different Postpartum Days in First‐ or Second‐Lactation Dairy Cows

Milk fatty acids (FA) are potential indicators of the nutritional status and reproductive performance of dairy cows. We investigated the relationship between FA until 125 days in milk (DIM) and the first insemination conception rates (CR) until 200 DIM. We used monthly test‐day milk and insemination records of Holstein cows during the first and the second lactations. FA compositions included de novo FA (DnF: C4:0–14:0) and preformed FA (C15:0 and ≥ C17:0) on a total FA basis. We investigated CR of cows with different FA levels and insemination DIMs. FA compositions tested within 35, 36–65, 66–95, and 96–125 DIMs were leveled as low, moderate, or high. Insemination DIMs were grouped as 66–95, 96–125, and 126–200 DIM. During the first lactation, the CR until 125 DIM was significantly lower in low DnF until 125 DIM than in moderate and high DnF. During the second lactation, the CR until 95 DIM was significantly lower in low and moderate DnF within 35 DIM than in high DnF. These results suggest that DnF within 125 DIM during the first lactation and within 35 DIM during the second lactation are associated with CR until 125 DIM and 95 DIM, respectively.