65. Does the Source of Trace Mineral Supplementation Influence Fiber Degradability in Beef Cattle?

Abstract This experiment evaluated dry matter intake (DMI) and ruminal degradability parameters of beef heifers fed forage-based diets supplemented with different sources of trace minerals. Fifteen rumen-cannulated Angus heifers (initial BW = 509 ± 25.2 kg) were housed in individual dry-lot pens and assigned to a completely randomized block design. Treatments consisted of sulfate (INR; n = 5), organic (ORG; n = 5), or hydroxy (HDX; n = 5) sources of trace minerals, with all heifers receiving equal amounts of a mineral premix containing 921 mg/kg Cu, 1,842 mg/kg Zn, and 1,228 mg/kg Mn. The experimental period lasted 32 days. Heifers were fed daily with chopped grass-mixed hay. From day 28 to 32, in situ ruminal degradability of the hay was evaluated. The hay was collected daily between days 2 and 8, dried in a forced-air oven at 55 °C for 72 h, and ground using a Wiley mill (2-mm screen). Approximately 9 g of hay were placed in nylon bags (10 cm x 20 cm; Ankom Tech. Corp., Macedon, NY, USA) and incubated in the rumen for 0, 3, 6, 12, 24, 48, 72, and 96 h. Two bags were used per incubation time. Bags were introduced into the rumen in reverse order so that all were removed simultaneously for rinsing. After washing, bags were dried at 55° C for 72 h, and the residues were analyzed for dry matter (DM) and neutral detergent fiber (NDF) content. The in situ DM profile was estimated using the equation proposed by Orskov and Mcdonald (1979): Y(t) = a + b × (1 −− e(− kdxt) ) and the NDF degradation parameters were estimated by the equation proposed by Van Milgen et al. (1991): RNDF(t) = b × [1 + (λ × t)]xe(− λxt) + I. No effects of treatment (P = 0.96) or treatment x day interaction (P = 0.20) were detected for DMI (Figure 1). Similarly, no treatment effects (P ≥ 0.62) were observed for fraction “a” (soluble fraction) or degradation rate (kd) of DM (Table 1). However, supplementation with HDX sources of trace minerals tended to increase (P = 0.06) fraction “b” (potentially degradable fraction). No treatment effects (P ≥ 0.13) were detected for fraction “I” (undegradable fraction), “kd”, or “λ” (joint fractional rate of latency and degradation) of NDF. Nonetheless, HDX supplementation increased (P = 0.02) fraction b of NDF. Overall, supplementation with HDX trace mineral sources positively influenced the potentially degradable fraction of nutrients, which may enhance nutrient utilization efficiency in beef heifers.