THE INFLUENCE OF MOLYBDENUM AND SULFUR ON VARIOUS COPPER PARAMETERS OF AFAUNATED RAM LAMBS OF DIFFERENT SIRE BREEDS

Abstract

Thirty-two afaunated ram lambs, sired by Dorset, Suffolk or Line M rams, were used in a randomized complete block experiment with repeated measures to study the effect of sire breed and dietary supplemental molybdenum ((NH4)6 Mo7O24°4H2O) and sulfur (Na2SO4) on selected criteria of copper (Cu) status. Criteria used included whole blood, plasma and liver Cu concentrations and plasma ceruloplasmin oxidase (CpOx) activity. The basal diet (64.2% crushed barley, 29.6% chopped alfalfa-brome hay) contained 7.7 mg Cu, 1.4 mg molybdenum (Mo) and 2.4 g sulfur (S) kg−1 dry matter (DM). Basal diet was fed to control lambs (Diet I). Mo and S were added to the premix such that diets fed to lambs assigned to Diets II, III and IV provided 1.4, 6.6 and 11.0 mg Mo kg−1 DM, and 3.8, 4.0 and 3.8 g S kg−1 DM, respectively. Dietary Cu concentrations fed to lambs in Diets II, III and IV were 7.4, 7.4 and 8.0 mg kg−1 DM, respectively. The diets were pelleted and fed free-choice with the alfalfa-brome hay for 105 d. Tap water was available to the animals at all times. Blood samples were taken by jugular venipuncture and liver samples by biopsy every 35 d. Total Cu was determined by atomic absorption spectrophotometry following wet ashing of the sample. Oxidase activity of a Cu-containing enzyme, CpOx, was also measured in plasma. Blood and plasma Cu were reduced (P < 0.01) in Diet III only. Liver Cu and CpOx activity were reduced (P < 0.05) in all supplemented groups. Diet IV had high blood and plasma Cu (> 15.7 μM L−1) when liver Cu (< 50 μg g−1 wet basis) and CpOx activity (< 40 ΔA min−1 L−1) were low, characteristic of conditioned Cu deficiency. The effect of S alone was inconclusive due to a 10-d contamination of Diet II with 28.3 mg Mo kg−1 DM. Diet by sire breed interaction, significant (P < 0.05) only with blood and plasma Cu data, suggests a genetic influence on Cu metabolism. Key words: Sheep, lambs, copper, sulfur, molybdenum, afaunation