RADIONUCLIDES IN MILK OF DAIRY HEIFERS RAISED ON FORAGES HARVESTED FROM PHOSPHATIC CLAY SOILS ON RECLAIMED MINED LAND

Alfalfa (AR; Medicago sativa L.) and corn (CSR; Zea mays L.) were grow n in phosphatic clay soils on phosphate-mined reclaimed land in centra l Florida. Corn (CSC) also was grown on unmined land and served as a c ontrol forage. Upon harvesting, plants were chopped and ensiled. Conce ntrations of Ra-226 averaged 2.44, 0.26, and 0.15; Pb-207 averaged 1.0 4, 0.63, and 0.52; and Po-210 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 a t approximately 24 mo of age. Samples of milk were collected on d 1, 1 5, and 30 of lactation and analyzed for radionuclides. Averaged across sampling days, heifers fed AR had greater milk concentrations of Ra-2 26 compared with those fed CSR (0.27 vs. 0.22 Bq kg-1 DM; P < 0.10), w hich, in turn, had greater milk concentrations compared with heifers f ed CSC (0.22 vs. 0.13 Bq kg-1 DM; P < 0.05). Heifers fed AR also had g reater milk concentrations of Po-210 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-2 10 was gr eater 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 a nd Cu concentrations suggested subclinical molybdenosis in heifers fed AR. However, all heifers grew at an acceptable rate, conceived normal ly, had normal gestation periods, gave high quality colostrum at calvi ng, and produced similar amounts of milk.