Effects of supplemental Zn concentration and trace mineral source on immune function and associated biomarkers of immune status in weaned beef calves received into a feedlot

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Abstract
Low risk, weaned Angus-crossbred steers (n = 72; 284 ± 25 kg) were used in a 42-d receiving study. Steers were housed in pens (n = 6 steers/pen) equipped with GrowSafe bunks for determination of individual animal feed disappearance. Dietary treatments (n = 24 steers/treatment) included: 1) TM from an organic source (Availa4; Zinpro Corp., Eden Prairie, MN) at 7 g∙steer -1∙d -1; for 42 d (ORG); 2) ORG for entire 42-d plus AvailaZn (Zn amino acid complex, Zinpro Corp., Eden Prairie, MN) to provide 1,000 mg Zn∙steer -1∙d -1for first 14 d (ORG+Z); 3) inorganic TM sources to supplemented at equivalent concentration as in ORG for 42-d (ING). Cattle were weighed on d -1, 0, 14, 41, and 42. Whole blood was collected (n = 72 steers) on d 0, 14, and 42. Liver biopsies were conducted (n = 36 steers; 3 steers/pen) on d 0, 14, and 42. Flow cytometry measures were conducted using whole blood on d 1, 14, and 42 for determination of circulating frequencies of immune cell populations. There was a tendency for improved overall ADG (P = 0.07) where both ORG and ORG+Z were greater than ING. Final BW did not differ (P = 0.21) and overall DMI was unaffected by dietary treatment (P ≥ 0.18). However, overall G:F was improved (P = 0.01) in steers supplemented organic TM (ORG and ORG+Z) compared to ING. Plasma Zn concentration did not differ at any timepoint during the study (P ≥ 0.20). Liver Zn concentration did not differ between treatments on d 0 or 42, however, on d 14 ING tended (P = 0.09) to be greater than ORG+Z with ORG being intermediate. Plasma Cu was unaffected by dietary treatment (P ≥ 0.34) on d 0, 14, and 42. Plasma Fe did not differ on d 0 or 42 but tended to be greater in ORG and ORG+Z compared to ING (P = 0.08) on d 14. Dietary treatment did not alter (P ≥ 0.22) liver Fe or Mn concentration at any timepoint. Frequency of total circulating NK and CD8 T cells measured on d 0, 14, 42 did not differ (P ≥ 0.07). However, cell surface markers of activation (CD16, CD44 and CD8) on NK cells measured on d 14 did differ because of treatment (P ≤ 0.05). Results presented herein indicate TM from an organic source supplemented to steers during receiving can positively influence growth rate and feed efficiency. Regardless of source, TM supplementation affected markers of immune function but did not influence the prevalence of circulating NK and CD8 T cell populations.
Funding Information
  • Zinpro Corporation

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