The effects of feeding increasing levels of added fat to growing-finishing pigs when fed with or without narasin (Skycis)

The objective was to evaluate the effects of feeding increasing energy by increasing fat (corn oil) levels to growing-finishing pigs when fed with or without narasin (Skycis; Elanco Animal Health, Greenfield, IN). A total of 2,194 pigs with an initial body weight of 35.6 ± 3.6 kg were housed in 88 mixed-sex pens (25 pigs/pen). Each treatment combination was replicated 11 times. Pigs were fed in a 4 × 2 factorial arrangement of treatments in a randomized complete block design. Factors included added fat level (0.0%, 1.3%, 2.6%, or 4.0%) and narasin (0 mg/kg or 15 mg/kg). Pigs were provided ad libitum access to feed and water throughout the study and weighed on day 0 (start of experimental feeding period), 30, 54, and 80. Pigs were marketed over the course of 4 wk with the heaviest pigs removed during each marketing event. There were significant interactions between narasin and energy on overall grow-finish average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed (G:F) (P ≤ 0.05). Pigs that were fed 0% added fat and 15 mg/kg narasin gained 0.03 to 0.04 fewer kg per day (<i>P</i> ≤ 0.05) compared to pigs fed 2.6% added fat and 15 mg/kg narasin and pigs fed 4% added fat with narasin or no narasin. Pigs fed 0% added fat and no narasin ate at least 0.10 more kg per day (<i>P</i> ≤ 0.03) compared to all other treatments. Pigs fed 0% added fat and no narasin had the lowest (<i>P</i> ≤ 0.01) gain to feed (G:F) by at least 0.009 compared to all other treatments. The G:F of pigs fed 0 mg/kg narasin increased (<i>P</i> ≤ 0.01) by approximately 0.01 with each increase in added fat level. However, when 15 mg/kg narasin was fed, there were no differences (<i>P</i> ≥ 0.06) in G:F between pigs fed 0% and 1.3% added fat, or between pigs fed 2.6% and 4% added fat. Adding narasin at 15 mg/kg improved G:F by 3.18% (<i>P</i> < 0.01) with 0% added fat but provided no additional benefits (<i>P</i> = 1.00) when fed with 4% added fat. The additive benefits of feeding narasin diminished on G:F as fat level increased and it may not be beneficial to include both additional fat and narasin at the same time to growing-finishing pigs.