Effect of supplementary copper source on copper status in growing beef heifers offered a diet naturally high in copper antagonists

Abstract Text: The bioavailability of Cu sources fed to ruminant animals has been the subject of many research articles due to its essentiality in bodily processes and the complexities between Cu and other minerals such as Mo, S and Fe, rendering Cu unavailable to the animal. As many of these complexes occur within the rumen, an attractive method of improving Cu bioavailability is to offer Cu sources which by-pass the rumen digestive process and are subsequently digested and absorbed in the abomasum and small intestine, respectively. This experiment evaluated the effect of three Cu sources on animal Cu status where diets naturally high in antagonists are fed. Sixty beef heifers (Bos taurus) were used in a randomized block design based on liver Cu content and offered one of four dietary treatments (n=15). These were: Control (Con), CuSO₄, Bioplex (Bio) and a novel Cu complex (NCu). The Con contained 20 mg Cu/kg DM whereas the other diets contained 54 mg Cu/kg DM. Animals were offered their basal diet of grass silage and concentrate (minerals: Fe, Cu, Mo and S at 703, 17, 5 and 1400 mg/kg DM). Treatments were fed individually on a daily basis whilst blood sampling and weights were taken on a weekly basis with a liver biopsy harvested at the beginning (d -7) and end (d 56) of the trial. There was no effect of treatment on live weight (404 kg, P = 0.77). However, animals offered NCu gained more weight (+ 0.18 ± 0.11 kg/d, P = 0.03) than those offered Con. Similarly, liver Cu at d 56 was higher (+132.5 ± 25 mg/kg DM, P < 0.01) for animals offered NCu than those offered Con; animals offered Bio and CuSO₄ were not different from other treatments. Plasma Cu levels were in the normal biological range for cattle and were lower in Bio supplemented animals compared to other groups (-0.16± 0.03 mg/L, P < 0.01). Similarly, caeruloplasmin was within the normal range for cattle but was higher for animals offered CuSO_4­ than those offered Bio (+3.41 ± 0.85 U/ml, P< 0.01). These results suggest that animals offered Con may have mobilized liver Cu to maintain Cu homeostasis in the blood as measured by caeruloplasmin and plasma Cu. The NCu complex gave the highest liver Cu concentration and weight gain, demonstrating the role of rumen protection of Cu in improving Cu bioavailability and animal performance.

Keywords: copper