PSV-7 Evaluation of Narasin Inclusion Level on Growth Performance and Carcass Characteristics of Growing-Finishing Pigs

Abstract

Abstract Previous studies evaluating 15 mg/kg of narasin have shown improvements in BW, ADG, and G:F. However, FDA approved labeling for narasin indicates improved G:F with increased inclusion levels (20 to 30 mg/kg), which may provide greater economic return with higher feed costs. Some commercial systems have shown improvements in ADG and G:F when feeding 20 or 30 mg/kg narasin compared with 15 mg/kg. As such, two studies were conducted to evaluate 30 mg/kg of narasin on growth performance and carcass characteristics of growing-finishing pigs. Studies were carried out using a randomized complete block design with three narasin levels: 0, 15, or 30 mg/kg. Study 1 (2,545 pigs) was carried out from 42.6 ± 1.3 kg to 132.9 ± 3.6 kg. Study 2 (1,235 pigs) was carried out over a fixed time of 112 days from 39.1 ± 3.0 kg to 139.8 ± 3.5 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 every 28 days and at every marketing event. Feed additions and feed remaining in the feeder at the time of pig weighing was recorded. Due to relatively low carcass recovery at the harvest facility, carcass data for Study 1 are not presented. Feeding 30 mg/kg of narasin did not improve (P > 0.05) growth or carcass performance compared with feeding 15 mg/kg narasin (Table 1). Compared with controls, feeding 15 mg/kg narasin increased final body weight (1.3 kg and 1.5 kg for Study 1 and 2, respectively), increased hot carcass weight (1.9 kg – Study 2), and improved carcass yield (0.4 percentage units), although differences were not always statistically different (P > 0.05). Overall G:F was improved 1.5% (P < 0.05) in Study 1, but not different (P > 0.05) than controls in Study 2. Results of this study confirm improvements in growth performance and carcass characteristics from feeding 15 mg/kg narasin to growing-finishing pigs. The outcomes of feeding 30 mg/kg of narasin were unexpected based on field outcomes and warrant further research.