Radionuclides in Milk of Dairy Heifers Raised on Forages Harvested from Phosphatic Clay Soils on Reclaimed Mined Land

Abstract

AbstractAlfalfa (AR; Medicago sativa L.) and corn (CSR; Zea mays L.) were grown in phosphatic clay soils on phosphate‐mined reclaimed land in central Florida. Corn (CSC) also was grown on unmined land and served as a control forage. Upon harvesting, plants were chopped and ensiled. Concentrations of 226Ra averaged 2.44, 0.26, and 0.15; 210Pb averaged 1.04, 0.63, and 0.52; and 210Po averaged 1.59, 0.59, and 1.26 Bq kg−1 DM for AR, CSR, and CSC, respectively. These forages were fed separately to Holstein dairy replacement heifers (Bos taurus) (n = 15 per forage) from approximately 9 to 25 mo of age. Heifers gave birth to calves at approximately 24 mo of age. Samples of milk were collected on d 1, 15, and 30 of lactation and analyzed for radionuclides. Averaged across sampling days, heifers fed AR had greater milk concentrations of 226Ra compared with those fed CSR (0.27 vs. 0.22 Bq kg−1 DM; P<0.10), which, in turn, had greater milk concentrations compared with heifers fed CSC (0.22 vs. 0.13 Bq kg−1 DM; P<0.05). Heifers fed AR also had greater milk concentrations of 210Po compared with heifers fed CSR (0.58 vs. 0.30 Bq kg−1 DM; P<0.10), but values of CSR‐fed heifers were not different from CSC‐fed heifers (0.45 Bq kg−1 DM). Lead‐210 was greater in milk from heifers fed CSR compared with those fed AR or CSC (1.38 vs. 0.94 and 0.92 Bq kg−1 DM; P<0.13), respectively. Plasma S and Cu concentrations suggested subclinical molybdenosis in heifers fed AR. However, all heifers grew at an acceptable rate, conceived normally, had normal gestation periods, gave high quality colostrum at calving, and produced similar amounts of milk.