Evaluation of essential oils and prebiotics for newborn dairy calves.

A blend of essential oils (EO; carvacrol, caryophyllene, -cymene, cineole, terpinene, and thymol) and prebiotics (arabinogalactans; Stay Strong; Ralco, Inc., Marshall, MN) was designed to promote immunity and stimulate appetite to diminish health challenges and stresses experienced by newborn calves. It was hypothesized that calves supplemented with the medium dose (2.5 g/feeding) of the commercial EO would demonstrate the optimal response. The study objective was to determine the optimal feeding rate of EO when added to a milk replacer (MR) compared with feeding a control or a yeast cell wall additive (YCW). One hundred Holstein calves from a commercial dairy farm were blocked by birth date and randomly assigned to 1 of 5 treatments. Treatments were a control (CON), a 24:20% CP:fat (as-fed basis) MR (24:20 MR) without EO; EO mixed into the 24:20 MR at a rate of 1.25 g/feeding (EO-0.5), EO mixed into the 24:20 MR at a rate of 2.5 g/feeding (EO-1.0), or EO mixed into the 24:20 MR at a rate of 3.75 g/feeding (EO-1.5); or 24:20 MR with YCW mixed in at a rate of 2 g/calf at each feeding. The 24:20 MR was fed in a bucket 2 times/d at a rate of 0.28 kg/calf daily for 14 d, which was increased to 0.43 kg/calf at 2 times/d until d 35 and then reduced to 1 time/d at d 36 to facilitate weaning at d 42. Decoquinate was added to the MR at 41.6 mg/kg for coccidiosis control. Calves were housed in individual hutches bedded with straw with ad libitum access to a 20% CP pelleted calf starter and water. All data were analyzed using PROC MIXED as a completely random design. Calves fed EO-0.5 demonstrated greater ( < 0.05) ADG (0.65, 0.71, 0.64, 0.64, and 0.63 kg/d for the CON, EO-0.5, EO-1.0, EO-1.5, and YCW, respectively) through d 56 compared with calves fed EO-1.0 and YCW and tended ( < 0.10) to have greater ADG than calves fed the CON and EO-1.5. Total BW gains were greater ( < 0.05) for calves fed EO-0.5 compared with calves fed EO-1.0 and YCW, with calves fed the CON and EO-1.5 being intermediate and similar. Body length and wither height gains (final - initial) were greater ( < 0.05) for calves fed EO-0.5 compared with calves fed the other treatments. Hip width gains were similar ( < 0.10) among treatments. Hip height gains were increased ( < 0.05) for calves fed EO-0.5 compared with calves fed the CON, EO-1.0, EO-1.5, and YCW. These results demonstrate that supplementing EO-0.5 (1.25 g/calf daily) in a 24:20 MR may be the optimal feeding rate to enhance growth rates compared with feeding a 24:20 MR and a 24:20 MR containing YCW or other inclusion rates of EO.