A meta-regression analysis to evaluate the effects of narasin on grow-finish pig performance.

ABSTRACT

Ionophores are feed additives that decrease gram-positive microbial populations by disrupting the ion transfer across cell membranes resulting in improved growth performance. Narasin (Skycis; Elanco Animal Health, Greenfield, IN) is an FDA-approved ionophore utilized for increased rate of weight gain and improved feed efficiency in growing-finishing pigs. A meta-regression analysis was conducted to evaluate the effects of added narasin in growing-finishing pig diets to predict its influence on average daily gain (ADG), feed efficiency (GF), and carcass yield. A database was developed containing 21 technical reports, abstracts, and refereed papers from 2012 to 2021 representing 35 observations for growth performance data in studies ranging from 35 to 116 d in length (overall data). In addition, within these 35 observations, individual period data were evaluated (143 observations) using weekly, bi-weekly, or monthly performance intervals (period data). Regression model equations were developed, and predictor variables were assessed with a stepwise manual forward selection procedure. The ADG model using the overall data included ADG, ADFI, and GF of the control group, added narasin dose, and narasin feeding duration categorized as longer or shorter than 65 d. Predictor variables included in the GF model using overall data were ADG, ADFI, and GF of the control group and added narasin dose. For carcass yield, the final model included ADFI and GF of the control group, added narasin dose, and narasin feeding duration of longer than 65 d. In the period model for ADG, the predictors included ADG, ADFI, and GF of the control group, added narasin dose, and average BW of the control group categorized into greater than or less than 105 kg. For period data for GF, the model selected ADG, ADFI, and GF of the control group and added narasin dose. Based on the results, the overall response to added narasin for ADG and GF was quadratic and tended to decrease as ADG and GF increased. A similar quadratic response was observed for the individual period data. In summary, using median values from the database for predictor variables, this meta-analysis demonstrated narasin would be expected to improve ADG between 1.06% and 1.65%, GF between 0.71% and 1.71%, and carcass yield by 0.31% when fed continuously for longer than 65 d.