Effects of trace element supplementation on apparent nutrient digestibility and utilisation in grass-fed zebu (Bos indicus) cattle

Trace element deficiencies in cattle are omnipresent, both in developing and industrialised regions. Little information is available on the effect of dietary trace elements on nutrient digestibility and utilisation, in spite of many deficiency-related symptoms suggesting a relevant role, such as loss of appetite in Zn deficiency and severe diarrhoea in Cu deficiency. The present study aimed to identify the early effects of dietary trace elements on nutrient utilisation in grass-fed zebu (Bos indicus) cattle. Adult bulls (n=8) were randomly assigned to a treatment: control or trace element supplementation (Zn, Mn, Cu, Se, I and Co) during 28 days. Grass mineral analysis suggested deficient Cu (5.53-9.60 mg/kg) and Se (0.02-0.09 mg/kg) concentrations in combination with high S (2577-3855 mg/kg) and Mo (1.52-3.12 mg/kg) and very high Fe (619-1214 mg/kg) concentrations. Supplementation increased plasma Cu (0.82 vs. 0.61 mg/l), Zn (1.40 vs. 0.89 mg/l), Mn (0.30 vs. 0.05 mg/l) and Se (0.07 vs. 0.06 mg/l) concentrations (all P<0.05). Faecal Cu, Zn, Mn and Se were also increased (P<0.05), as was faecal Co (P=0.05) concentration in supplemented bulls. On the contrary, trace element supplementation did not affect plasma ceruloplasmin and superoxide dismutase activities (P>0.05). Also, no effects on apparent nutrient (dry matter, ash, protein, fat, and fibre) digestibility, apparent trace element absorption (except for Se and I) or plasma acyl carnitines (indicators of available energy substrates) were observed in this study (all P>0.05). Overall, despite clear improvement in trace element status - notwithstanding high concentrations of Cu antagonists in the grass diet - supplementation did not affect nutrient digestibility or utilisation in grass-fed zebu cattle.