Two hundred eighty-two cows were assigned to a 40-week experiment to determine the efficacy of zinc amino acid complex (CZ), with or without cobalt glucoheptonate and amino acid complexes of manganese and copper, in preventing facial eczema (FE). Apart from 25 control cows, which received no supplemental zinc, manganese, copper, and cobalt throughout treatment periods, remaining 257 cows were randomly allocated to 1 of 4 treatments across two periods. Calving and pre-FE season was designated Period 1 (weeks 1-23) while FE season was designated Period 2 (weeks 24-40). The four treatment groups by period were: 1) 360mg zinc/d from CZ in Period 1, and 720mg zinc/d from CZ in Period 2 (2XCZ); 2) 360mg zinc/d from CZ in Period 1, 1440mg zinc/d from CZ in Period 2 (4XCZ); 3) 360mg zinc/d, 200mg manganese/d and 125mg copper/d from amino acid complexes and 12mg cobalt/d from cobalt glucoheptonate in Period 1, and 1440mg zinc/d, 200mg manganese/d and 125mg copper/d from amino acid complexes and 12mg cobalt/d from cobalt glucoheptonate in Period 2 (ZMC); and 4) no supplemental zinc in Period 1 and 17.4pl0.4g zinc oxide every 2days in Period 2 (ZnO). In addition to monitoring cows for clinical symptoms of FE, serum samples were collected every 1 to 4weeks and analyzed for glutamate dehydrogenase (GDH) and gamma glutamyl transferase (GGT) activities to determine the efficacy of treatments in preventing FE. Pasture samples were collected weekly for spore counting to determine FE challenge. During week 30, serum GDH activities of 3 cows in ZMC treatment group were >200IU/L, and 2 other ZMC-treated cows had increasing serum GGT activities, prompting inclusion of 40mg zinc/kg BW from zinc oxide every 2days for FE prevention. During week 39, ZnO treatment was extended to cows in 2XCZ, 4XCZ and control groups as 3 cows were suffering from FE and serum GGT activities of all cows were 1.5 times greater than cows fed ZnO. Supplementing cows with up to 1440mg zinc/d from CZ, with or without cobalt glucoheptonate and amino acid complexes of manganese and copper, was ineffective in preventing FE.
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