Effect of narasin addition in mineral mixture on gain and intake of feedlot Nellore heifers

Narasin, an ionophore used in poultry, improved BW gain and feed efficiency in cattle fed high forage. However, there is little information about the effect of narasin for cattle fed a high-grain diet. The objective of this study was to determine the effect of adding narasin in the mineral mixture (MM) on gain and intake of feedlot Nellore heifers fed a high-grain diet. Sixty heifers at 12 ± 1 mo of age were assigned to a randomized complete block design, defined by initial BW (244 ± 4 kg), and housed in 20 pens (3 per pen). The experimental treatments were either a control, with no narasin added, or Narasin, with 1,300 mg of narasin per kilogram of MM. The diet was composed of 15.8% (DM basis) sugar cane bagasse, 70.8% ground corn, 12.9% soybean meal, and 0.5% urea. Treatments were arranged in a crossover design (all pens underwent all treatments) with 2 experimental periods of 28 d each, and between periods, there was a 7-d washout. Heifers were weighed at the beginning and at the end of each experimental period to calculate ADG. All days, MM was offered and orts were collected to calculate the MM intake (MMI). The ADG and feed efficiency were submitted to ANOVA by the MIXED procedure (SAS 9.3). The DMI and MMI were analyzed as repeated measures over time using the same procedure. The statistical model was composed by effect of treatments, periods, and pens. The addition of narasin in MM did not affect DMI (6.59 for the control and 6.55 kg/d for the Narasin treatment [SEM 0.25, P = 0.56]), MMI (57.6 for the control and 55.6 g/d for the Narasin treatment [SEM 11.9, P = 0.33]), and ADG (1.09 for the control and 1.17 kg for the Narasin treatment [SEM 0.04, P = 0.06]). However, the addition of 1,300 mg of narasin/kg of MM increased feed efficiency compared with the control treatment (0.165 for the control and 0.179 for the Narasin treatment [SEM 0.01, P = 0.05]). Based on DMI and MMI, the narasin intake was 10.6 mg/kg. The inclusion of narasin in MM increased feed efficiency in feedlot Nellore heifers fed a high-grain diet without affecting MMI and DMI.