Effect of Copper Source and Level on the Rate and Extent of Copper Repletion in Holstein Heifers

Abstract

The objective of this study was to evaluate the rate and extent of Cu repletion in Holstein heifers using two Cu sources (organic and inorganic) at two levels (15 and 30mg/kg). An additional repletion treatment included a Cu oxide bolus. Heifers (n = 50) were individually fed a total mixed ration fortified with S and Mo at 0.40%, and 15mg/kg of dry matter of the total diet, respectively. After 111 d of depletion, heifers were stratified by liver Cu concentration and randomly allotted to one of five repletion treatments. Four treatments consisted of feed sources of Cu (feed-Cu), 1) CuSO4 at 15mg/kg; 2) CuSO4 at 30mg/kg; 3) Availa-Cu at 15mg/kg; and 4) Availa-Cu at 30mg/kg. Availa-Cu is an organic Cu source that produces a Cu-amino acid complex. A fifth treatment, consisting of an intraruminal bolus (IB), provided a single dose of 25g of CuO needles. Repletion treatments were delivered in the same total mixed ration without supplemental S and Mo. Copper status was assessed in blood and liver samples collected on 14-d intervals for 70 d. Irrespective of treatment, all heifers increased in body weight during the repletion period. Liver Cu increased in each feed-Cu treatment over time. Heifers treated with an IB reached a peak in liver Cu concentration (165.5mg/kg) on d 28. Mean liver Cu concentrations were higher in heifers receiving 30mg/kg of Cu compared with heifers receiving 15mg/kg of Cu. Red blood cell superoxide dismutase (SOD) activity was higher (P<0.001) in heifers receiving CuSO4 than Availa-Cu (0.98 vs 0.87 U). Also, SOD activity was higher when heifers were supplemented with 30 vs 15mg/kg Cu (0.98 vs 0.87 U). Heifers receiving the Cu IB had higher SOD activity than heifers receiving feed-Cu sources (1.03 vs 0.92 U). Plasma ceruloplasmin concentration was higher (P<0.001) in IB-treated heifers vs. other treatments. No differences in plasma ceruloplasmin were detected for feed-Cu source or level. These results indicate that all Cu sources evaluated in this study elevated Cu status of depleted heifers, particularly when provided at higher dietary levels.