137 Evaluation of Narasin Inclusion Level on the Growth Performance and Carcass Characteristics of Growing-finishing Pigs

Two studies were conducted to evaluate narasin inclusion level on the growth performance and carcass characteristics of growing-finishing pigs. The studies were carried out using a randomized complete block design with three narasin levels: 0 vs. 15 vs. 20 mg/kg. Study 1 (2,232 pigs) was carried out over a fixed time of 85 days from 33.4 ± 1.7 kg to 117.0 ± 2.6 kg. Study 2 (1,125 pigs) was carried out over a fixed time of 113 days from 28.0 ± 2.2 kg to 124.4 ± 6.0 kg. All pigs were fed diets that met or exceeded nutrient recommendations of growing-finishing pigs (NRC, 2012). Pigs were offered ad libitum access to feed and water throughout the study and weighed on day 0, 28, 56, and 84. Feed additions and feed remaining in the feeder at the time of pig weighing was recorded. Due to disruptions at the slaughter facility, carcass data were not collected on Study 1. For Study 2, pigs were sent for slaughter over five weeks, with the heaviest 20% of each pen being sent for slaughter each week. At slaughter, hot carcass weight was collected. Compared to controls, feeding 15 mg/kg narasin increased (P < 0.05) final body weight (1.2 kg and 1.4 kg for Study 1 and 2, respectively), increased (P < 0.05) hot carcass weight (1.3 kg), and tended (P = 0.07) to improve carcass yield (0.3 percentage units). Feeding 20 mg/kg narasin increased (P < 0.05) overall G:F compared to controls (1.5% and 1.9% for Study 1 and 2, respectively). There were limited differences between the 15 and 20 mg/kg narasin levels. The results of this study confirm improvements in growth performance and carcass characteristics from feeding narasin to growing-finishing pigs. The outcomes of feeding 20 mg/kg narasin were unexpected and warrant further research.