Stress induction affects copper and zinc balance in calves fed organic and inorganic copper and zinc sources.

This study determined whether Cu and Zn balance was affected by feeding either Zn methionine (ZnMet) + Cu lysine (CuLys) or Zn sulfate (ZnSO4) + Cu sulfate (CuSO4) before and after stressing calves. Eight Charolais crossbred steer calves weighting 167 +/- 5 kg were randomly assigned to two treatments in a crossover experimental design. The millet hay and soybean meal diet when supplemented with the inorganic salts provided 9.2 ppm of Cu and 36.6 ppm of Zn or when fortified with the metal complexes contained 10.5 ppm of Cu and 36.6 ppm of Zn. Gentled calves were fed their respective diets for 28 d before an 18-d mineral balance trial was conducted. Collection consisted of five periods: 1) a 5-d baseline period, 2) 3 d of no Cu and Zn supplement, 3) 3 d of stress consisting of feed and water restriction and ACTH (80 IU) injections i.m. every 8 h, 4) 3 d of refeeding with no Cu and Zn supplement, and 5) 4 d of Cu and Zn repletion. Calves fed CuLys had 53% greater apparent Cu absorption and increased Cu retention (P < .05) during repletion compared with calves fed CuSO4. The 18-d mean retention of Cu from CuLys was greater (P < .05) than that from CuSO4. No differences (P > .05) in apparent absorption or retention of Zn were found between Zn sources, although during the 18-d trial mean retention was 58% higher when ZnMet was fed. Urinary Cu and Zn excretion decreased (P < .01) during stress.(ABSTRACT TRUNCATED AT 250 WORDS)