Prepartum blood lead concentrations linked to subsequent cyclicity in high-producing dairy cows in a non-industrial area

This study sought to identify the possible presence of lead (Pb) in blood and if detected to examine the relationship between blood Pb concentrations during the transition period and subsequent reproductive performance in high-producing dairy cows reared in a non-industrial area. Forty seven multiparous dairy cows were examined and/or sampled on Days 251-257 of gestation (visit 1,V1), the day of calving (V2) and on Days 8-14 (V3), 15-21 (V4), 22-28 (V5), 29-35 (V6), 36-42 (V7) and 50-56 (V8) postpartum. A mean level of 130±17 ppm (± SD) of Pb was detected in feed samples. Blood samples were collected for Pb determination from V1 to V5 and lead was present in all collected blood samples. One unit increase in blood Pb concentration in the V1 sample led to a 0.3-fold reduction (P=0.02) in the likelihood of a cow being cyclic. Mean blood Pb concentrations were 0.97±0.11 and 2.6±0.1 μg/L for cyclic (n=24) and non-cyclic (n=23) cows, respectively. Cows with a body condition score (BCS) loss of ≥0.75 units between V1 and V4 (n=24) showed higher Pb concentrations throughout the study period than the remaining cows (n=23; P <0.001). In conclusion, blood Pb levels were detected in all cows. Prepartum blood Pb concentrations were negatively related to subsequent cyclicity. Cows with higher Pb levels experienced a greater BCS loss during the transition period. Routine blood Pb tests could indicate a higher risk of anoestrus in cows with higher Pb concentrations.