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

## TL;DR

This study examines how adding fat and narasin affects the growth and feed efficiency of pigs, finding that narasin's benefits decrease with higher fat levels.

## Contribution

The novel contribution is identifying diminishing returns of narasin when combined with high-fat diets in growing-finishing pigs.

## Key findings

- Adding narasin improved growth efficiency but only at low fat levels.
- Pigs on 0% fat diets without narasin had the worst feed conversion.
- Narasin's benefits disappeared when fat levels exceeded 2.6%.

## Abstract

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 (P ≤ 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 (P ≤ 0.03) compared to all other treatments. Pigs fed 0% added fat and no narasin had the lowest (P ≤ 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 (P ≤ 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 (P ≥ 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% (P < 0.01) with 0% added fat but provided no additional benefits (P = 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.

Narasin (Skycis) is an ionophore fed to growing/finishing pigs to improve growth rate and feed conversion. However, the benefits of narasin may diminish when fed in conjunction with diets containing higher fat (i.e., greater energy) levels. The objective of this trial was to evaluate the interactive effects of increasing energy by increasing corn oil (tested fat source) inclusion in the diets of finishing barrows and gilts fed with and without narasin.