Determination of the transfer of lead and chromium from feed to raw milk in Holstein cows.

In this study, we aimed to determinate the transfer of lead (Pb) and chromium (Cr) from feed to raw milk in Holstein cows. Solutions of lead acetate and chromium (III) nicotinate were added together at different levels to individual portions of feed on a daily basis. Lead administration for the low-, middle- and high-dosage groups was controlled as 0.9, 1.8 and 3.6 g/day for 30, 30 and 25 days, while chromium was feed at 0.47, 1.5 and 4.7 g/d for 40, 40, and 40 days, respectively. A sensitive graphite furnace atomic absorption spectrometry (GFAAS) method was developed and optimised with a respective limit of detection of lead and chromium found to be 1 and 5 μg kg-1 raw milk. The optical wavelengths for detection of lead and chromium were 283.31 nm and 357.87 nm respectively. The results showed that the highest concentrations of lead in raw milk for the low-, middle- and high-dosage groups were 0.083 ± 0.021, 0.215 ± 0.064 and 0.232 ± 0.035 mg kg-1 , which displayed a positive correlation with dosage levels. In addition, a high dosage level accompanied a greater rate of loss of lead contents after dosing withdrawal. However, chromium concentrations maintained a relatively stable range around 0.1 mg kg-1 raw milk for all dosing groups and showed little transfer from feed to raw milk through the whole experiment.