Effects of tri-basic copper chloride versus copper sulfate provided in corn- and molasses-based supplements on forage intake and copper status of beef heifers

¹ University of Florida - IFAS, Range Cattle Research and Education Center, Ona, 33865
² Department of Animal Sciences and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695

^* To whom correspondence should be addressed. E-mail: jdarthington{at}ifas.ufl.edu.

	Abstract

The objective of this study was to investigate the effect of supplemental tri-basic copper chloride (Cu₂(OH₃)Cl; TBCC) vs. Cu sulfate (CuSO₄) on Cu status and voluntary forage DMI in growing heifers. Two, 90-d experiments were conducted using 48 non-pregnant, crossbred heifers (24 heifers/experiment) (355 ± 10.7 and 309 ± 9.9 kg for Exp. 1 and 2, respectively). In each experiment, 3 supplemental Cu treatments were randomly allocated to heifers in individual pens, consisting of 1) 100 mg Cu/d from CuSO₄, 2) 100 mg Cu/d from TBCC, or 3) 0 mg Cu/d. The 2 experiments differed by the form of supplement used to deliver the Cu treatments (corn- vs. molasses-based supplements for Exp. 1 and 2, respectively). Supplements were formulated and fed to provide equivalent amounts daily of CP and TDN, but differed in their concentration of the Cu antagonists; Mo (0.70 vs. 1.44 mg/kg), Fe (113 vs. 189 mg/kg), and S (0.18 vs. 0.37%) for corn- and molasses-based supplements, respectively. All heifers were provided free-choice access to ground stargrass (Cynodon spp.) hay. Jugular blood and liver biopsy samples were collected on d 0, 30, 60, and 90. Heifer BW was collected on d 0 and 90. Heifer ADG was not affected by Cu treatment (average = 0.22 ± 0.11 and 0.44 ± 0.05 kg for Exp. 1 and 2, respectively; P > 0.20). In Exp. 1, heifers provided supplemental Cu, independent of source, had greater (P < 0.05) liver Cu concentrations on d 60 and d 90 compared with heifers provided no supplemental Cu. In Exp. 2, average liver Cu concentrations were greater (P = 0.04) for heifers receiving supplemental Cu compared with heifers receiving no Cu; however, all treatments experienced a decrease in liver Cu concentration over the 90-d treatment period. Plasma ceruloplasmin concentrations did not differ in Exp. 1 (P = 0.83), but were greater (P = 0.04) in Exp. 2 for heifers receiving supplemental Cu compared with heifers receiving no Cu. In Exp. 1, voluntary forage DMI was greater (P < 0.05) for heifers provided supplemental Cu, independent of source, compared with heifers provided no Cu. In contrast, voluntary forage DMI was not affected (P > 0.10) by Cu supplementation in Exp. 2. These data imply that CuSO₄ and TBCC are of similar availability when offered to growing beef heifers in both corn- and molasses-based supplements. However, corn- and molasses-based supplements appear to impact Cu metabolism differently. These impacts may affect voluntary forage DMI in growing beef heifers.

Key Words: cattle, copper, heifer, corn, molasses