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Effect of specific essential oil blend on performance of Nellore young bulls in feedlot
The European Union has prohibited the use of growth-promoting antibiotics in animal feeds. These restrictions, based around concerns that the use of antibiotics for livestock can give rise to transmissible resistance factors that may compromise the therapeutic use of antibiotic in humans (Casewell et al., 2003). In this sense, natural plant products such as essential oils (EO) become an alternative to manipulate rumen fermentation (Iason, 2005). Chao et al., 2000 suggested that gram-negative bacteria’s shows a trend to have higher resistance to essential oils than gram-positive bacteria. Decreasing gram + bacteria may improve animal performance. Therefore, seventy two Nellore bulls (375 ± 14 kg BW) were fed 15% of sugar-cane bagasse and 85% of concentrate for 81d in individual pens. The treatments compound different combinations of essential oil blend or monensin (M) or both (1*: 100mg EO; 2*: 20 mg of M + 100 mg of EO; 3*: 20 mg of M + 200 mg of EO; 4*: 200 mg of EO; 5*: 20 mg of M and 6*: 10 mg of M + 100 mg of EO). Treatment mixes were incorporated into the concentrate ration, which was composed by corn, soybean meal and citrus pulp. Diets were isoenergetic and isonitrogenous. Throughout the entire experimental period, the provided feed amounts were adjusted to allow approximately 100g/kg residue comparing with the total consumed on previous day. Average daily gain was calculated using the initial and final individual live weight divided by the number of experimental days. Data was subjected to analysis of variance compared by orthogonal contrast. Animals fed 20mg of M had the greatest liveweight gain (1.242 kg/d), treatments 20mg of M + 100mg of EO and 100mg of EO achieved 0.909 and 0.910kg/d, respectively. Animals supplemented with 10mg of M + 100 mg of EO and 20mg of M + 100mg of EO had lower average daily gain than 5* but higher than 2*. However, 6* and 3* were not statistically different, the ADG for this treatment were 1.174 kg/d and 1.008 kg/d, respectively. The data of feed conversion (kg DM/ADG) shown for treatment 1* feed intake of 9.278 kg DM/d to gain 1kg liveweight, and the treatments 2*, 3*, 4*, 6*; 9.196, 8.398, 8.244, 8.385, respectively. Animals the treatment 5* had the lower intake (7.137). Therefore, strategic use of essential oil did not improve the animal performance.
Keywords: Essential oil, feedlot, monensin.