Evaluation of Three Copper Sources on Measures of Forage Utilization and Copper Status in Beef Cattle

Abstract Text: We investigated the effect of Cu source on measures of subtropical forage utilization and Cu status in beef cattle.  In Exp. 1, 24, 2-year old heifers (371 ± 48.1 kg) were individually fed limpograss hay and 2.1 kg/d of a molasses-based supplement (8.3 and 3.0 mg Cu/kg DM, respectively). Treatments were assigned to heifers consisting of, (1) no Cu, and 100 mg Cu/d from (2) hydroxy Cu (IntelliBond; Micronutrients, Inc.), (3) organic Cu (Bioplex; Alltech Inc.), or (4) Cu sulfate. Forage DMI and liver Cu change was assessed over 33 d. In Exp. 2, forage DMI and DM, N, and NDF in situ ruminal disappearance was evaluated in 4 ruminally-fistulated steers using a 4 x 4 Latin square design with 4, 20-d periods with the same treatments as Exp. 1. Periods consisted of 10 d of no Cu, 7 d adaptation, and 5 d in situ bag incubation.  Dried and ground bermudagrass (4 g) was placed into polyester bags and duplicate samples were incubated for 0, 3, 6, 9, 12, 24, 48, and 72 h. The non-linear model used was P=A+B [1-exp(-c x t)]. In Exp. 1, supplemental Cu had no effect (P = 0.40) on voluntary forage DMI; however, heifers provided hydroxy Cu tended (P = 0.07) to consume less hay than heifers consuming organic Cu (1.31 vs. 1.46% BW).  All heifers experienced a decrease (P < 0.001) in liver Cu; however, heifers consuming no Cu tended (P = 0.12) to have a greater decrease vs. all other treatments, and heifers provided hydroxy Cu tended (P = 0.14) to have a lesser decrease than heifers consuming organic Cu (-94, -80, -64, and -44 mg/kg DM for no Cu, organic Cu, Cu sulfate, and hydroxy Cu, respectively). In Exp. 2, the DM, N, and NDF fractions were described as A, rapidly degradable; B, potentially degradable; and C, undegradable. There was no effect (P ≥ 0.15) of treatment on forage DMI and in situ DM disappearance. Fraction A NDF and N did not differ among treatments; however, NDF fraction B tended (P < 0.06) to be greater for steers provided organic Cu vs. all other treatments (48.7 vs. 41.2%).  Similarly, N fraction B was greater (P = 0.03) for steers receiving organic Cu vs. hydroxy Cu and No Cu (29.2 vs. 19.0%).  These results imply that the organic Cu source utilized in these studies may positively influence the digestibility of subtropical forages.

Keywords: copper, digestibility, cattle