SUPPLEMENTARY COPPER FOR GROWING CATTLE CONSUMING DIETS HIGH IN MOLYBDENUM OR MOLYBDENUM PLUS SULFUR

Abstract

Forty-eight Cu-depleted beef steers were used in a 105-d growing trial to compare four methods of Cu supplementation. Corn silage-barley concentrate diets were supplemented to contain 10 mg kg−1 dry matter (DM) Mo, and 1.3 (low S) or 3.7 (high S) g kg−1 total S. Copper treatments within low and high S diets were: (1) no supplemental Cu (0Cu); (2) a dietary supplement of 10 mg kg−1 DM Cu in the complete feed, added as CuSO4∙5H2O to the concentrate (CuSO4); (3) 20 g copper oxide needles (CuON) orally dosed on day 0; and (4) injectable Cu (ICu) on day 0. Although average daily gain was not different (P > 0.05) among Cu treatments, DM intake was lower (P < 0.05) with CuSO4 and CuON than with 0Cu or ICu. Feed efficiency (FE; feed:gain ratio) was better (P < 0.05) with CuSO4 (FE = 5.60) than 0Cu (FE = 6.88), while CuON (FE = 6.04) and ICu (FE = 6.16) FE were intermediate to 0Cu and CuSO4. Increasing dietary S from 1.3 to 3.7 mg kg−1 DM resulted in lower (P < 0.01) concentrations of Cu and Mo in liver and plasma, and plasma ceruloplasmin activity. An improvement of FE with CuSO4 was related to increased Cu and lower Mo concentrations in the plasma and liver of steers. With ICu there was some indication of an improvement of Cu status. With CuON, measured parameters were indicative of a metabolic Cu insufficiency, but with a lower concentration of Mo in plasma. At the levels of supplementation used in this trial, CuSO4 was a better Cu supplement than CuON or ICu for cattle consuming diets containing excess Mo or Mo plus S. Key words: Cattle, molybdenum, sulfur, copper sulfate, copper oxide needles, injectable copper