BIOAVAILABILITY OF COPPER PROTEINATE AND COPPER CARBONATE RELATIVE TO COPPER SULFATE IN CATTLE
J.D. Ward and J.W. Spears
Introduction
Copper (Cu) deficiency is often a problem in cattle. Copper deficiency can be caused by the presence of Cu antagonists such as molybdenum (Mo) and sulfur (S) in the diet. Sulfur and Mo are thought to interact with Cu in the rumen, forming insoluble Cu com pounds that are not absorbed in the small intestine. It would be desirable to find a form of Cu that would not interact with Mo and S in the rumen and remain bioavailable. Copper carbonate has lower water solubility than CuSO4. This could cause CuCO3 to be resistant to interaction with Mo and S in the rumen and be more bioavailable than CuSO4. Therefore, the following experiments were performed to determine the relative bioavailabilities of CuCO3, Cu proteinate, and CuSO4 in the presence of high and low dietary concentrations of Mo.Materials and Methods
Two experiments were conducted to determine the bioavailability of CuCO3 and copper proteinate (CuProt) relative to CuSO4. In Experiment 1, 30 Cu- depleted Angus heifers were used in a 21-d repletion trial. Animals were limit fed a corn silage-soybean meal diet. Treatments consisted of: control, CuSO4, CuProt from Chelated Minerals Corpora tion (CuProtC), CuProt from Nutribasics (CuProtN), and CuCO3. All Cu sources were fed in .23 kg of ground corn to provide 50 mg of Cu per d. Blood was collected at 7-d intervals throughout the experiment. Plasma was analyzed for Cu concentration. A liver biopsy was obtained at the beginning and end of the experiment.Heifers were then fed Mo to depress there Cu status and reassigned to new treatments. Treatments were: no supplemental Cu (control), 5 ppm of supplemental Cu as CuSO4, 5 ppm of supplemental Cu as CuCO3, and 5 ppm of supplemental Cu as CuProtC. The diets consisted of corn silage supplemented with protein. All diets contained 5 ppm of supplemental Mo as Na2MoO4.2 H2O and .15% supplemental S as CaSO4. Heifers were weighed and bled before feeding on d 0, 10, 28, and 54. On d 57 a liver biopsy was obtained as before.
Results and Discussion
On d 21 the Cu-supplemented heifers had greater plasma Cu concentrations than control heifers, but there were no differences among the supplemented heifers at the end of the study and they all had plasma Cu concentrations greater than .8 mg/L which is above the level (.6 mg/L) that is indicative of Cu deficiency in cattle .Based on the data from d 21, all Cu sources could be considered to be equal in bioavailability for Cu deficient cattle. However, liver Cu concentrations indicate that little Cu was stored in the livers of the CuCO3 supplemented heifers and the final liver Cu concentrations of these heifers did not differ from control heifers. The CuSO4, CuProtN, and CuProtC supplemented heifers had greater (P << .01) liver Cu concentrations than control heifers but there were no differences among these three groups of Cu- supplemented heifers. Based on liver Cu concentrations CuCO3 was not as bioavailable as CuSO4 or the two CuProt.
The second experiment was designed to determine the bioavailability of different Cu sources when 5 ppm of Mo was added to the diet. A form of Cu that is insoluble in the rumen, but becomes soluble further down the digestive tract such as in the abomasum might resist interactions with thio molybdates and be more bioavailable than Cu sources that are soluble in the rumen. Both CuCO3 and CuProtC have the desirable characteristics of low water solubility coupled with a high solubility in acid. Therefore, we compared these two sources of Cu to CuSO4 when Mo was added to the diet.
Feed intake and gain were not different among treatments. On d 54 the CuProtC supplemented heifers showed no change from d 0 in plasma Cu concentra tions. Control and CuSO4 supplemented heifers had declining (P << .01) plasma Cu concentrations and were similar to each other throughout the 54-d study. Copper carbonate supplemented heifers showed little change in plasma Cu concentrations throughout the experiment.
Based on changes in plasma Cu concentrations both CuProtC and CuCO3 appeared to be bioavailable in spite of the presence of high levels of Mo and S in the diet. However, CuCO3 supplemented heifers had more stored Cu in their livers at the beginning of the experiment than control (P << .05) and CuProtC- supplemented (P << .09) heifers. However, the liver Cu concentrations of the CuCO3 supplemented heifers were similar to the liver Cu concentrations of the CuSO4 supplemented and control heifers at the end of the experiment. Therefore, it appears that the CuCO3 supplemented heifers were able to maintain their plasma Cu concen trations by mobilizing Cu stored in their livers. Control, CuSO4, and CuCO3 supplemented heifers had declining liver Cu concentrations whereas the CuProtC supplemented heifers showed no change in liver Cu concentrations. Therefore, it appears that 5 ppm of supplemental Cu from CuProtC was adequate to provide enough Cu to the heifers to maintain their Cu status while this level of Cu fed as either CuSO4 or CuCO3 was inadequate to meet the Cu requirements of the heifers.
Implications
When low levels of Mo are present in the diet of cattle, CuSO4 and CuProt appear to be equally effective in supplying Cu to cattle and the cheapest most convenient Cu source should be fed. However, when Mo is present in the diet in greater concentra tions, some forms of CuProt may be more bioavailable than CuSO4 and may be advantageous. Copper carbonate supplementation does not appear to increase liver Cu concentrations and may be less bioavailable as a Cu source for cattle.
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