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

Abstract

Narasin (Skycis®, Elanco Animal Health) is an ionophore used in the United States pork industry to increase rate of weight gain (ADG) of growing-finishing pigs. It is also well established that adding dietary fat can improve ADG and feed efficiency of pigs. Therefore, the objective was to evaluate the effects of feeding increasing energy by increasing fat (vegetable oil) levels to growing-finishing pigs when fed with or without narasin. 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. Pens were marketed over the course of 4 weeks with the heaviest pigs removed during each marketing event. As expected, ADG (1.87%) and gain:feed (G:F;7.89%) improved (P< 0.01) by increasing added fat to 4% from 0%. At the same time, ADFI decreased (P< 0.01) 3.23% as added fat increased from 0% to 4%. Average daily feed intake decreased (P=0.02) by 1.09% and G:F increased (P≤0.01) 2.56% by feeding 15 mg/kg compared to 0 mg/kg narasin. There was an interaction (P=0.05) on ADG. Pigs that were fed 0% added fat and 15 mg/kg narasin gained 0.03-0.04 fewer kg per day (P≤0.05) compared to pigs fed 2.6% added fat and 15 mg/kg narasin and pigs fed 4% added fat with or without narasin. There was an interaction (P< 0.01) on ADFI. Pigs fed 0% added fat and no narasin ate at least 0.10 more kg/d (P≤0.03) compared to all other treatments. There was an interaction (P< 0.01) on G:F. Pigs fed 0% added fat and no narasin had the lowest (P≤0.01) G:F by at least 0.01 compared to all other treatments. The G:F of pigs fed 0 mg/kg narasin increased (P≤0.01) by 0.01 with each increase in added fat level. However, when 15 mg/kg narasin was fed, there were no differences (P≥0.06) in G:F between pigs fed 0% and 1.3% added fat, or pigs fed 2.6% and 4% added fat. Overall, increasing energy by increasing fat improved G:F regardless of narasin inclusion. However, adding narasin at 15 mg/kg improved G:F by 2.63% (P< 0.01) with 0% added fat but provided no additional benefits (P=1.00) when fed with 4% added fat. In conclusion, the benefits of feeding narasin on cumulative G:F decreased with added fat, and feeding both simultaneously may not provide additional benefit.