Residual effect of narasin on feed intake and rumen fermentation characteristics in Nellore steers fed forage-based diet

Letícia Carolina Bortolanza Soares; Rodrigo S Marques; Alexandre Vaz Pires; Vinicius Alves Cruz; Makayla Anne Ogg; Arnaldo Cintra Limede; Paulo César Gonzales Dias Junior; Isabela Jorge Dos Santos; Rhaíssa Garcia de Assis; Vinícius N Gouvêa; Evandro Maia Ferreira; Daniel Montanher Polizel

doi:10.1093/tas/txad027

Residual effect of narasin on feed intake and rumen fermentation characteristics in Nellore steers fed forage-based diet

Transl Anim Sci. 2023 Mar 10;7(1):txad027. doi: 10.1093/tas/txad027. eCollection 2023 Jan.

Authors

Affiliations

¹ Department of Nutrition and Animal Production, FMVZ, University of São Paulo, Pirassununga, SP 13635-000, Brazil.
² Department of Animal and Range Science, Montana State University, Bozeman, MT 59717, USA.
³ Department of Animal Science, College of Agriculture "Luiz de Queiroz", University of São Paulo, Piracicaba, SP 13418-900, Brazil.
⁴ Texas A&M AgriLife Research and Extension Center, Amarillo, TX 79106, USA.

Abstract

This study aimed to evaluate the residual effect of narasin on intake and ruminal fermentation parameters in Nellore cattle fed a forage-based diet. Thirty rumen-cannulated Nellore steers [initial body weight (BW) = 281 ± 21 kg] were allocated to individual pens in a randomized complete block design, with 10 blocks and 3 treatments, defined according to the fasting BW at the beginning of the experiment. The animals were fed a forage-based diet containing 99% Tifton-85 haylage and 1% concentrate. Within blocks, animals were randomly assigned to one of three treatments: (1) forage-based diet without addition of narasin (CON; n = 10), (2) CON diet plus 13 mg of narasin/kg DM (N13; n = 10), or (3) CON diet plus 20 mg of narasin/kg DM (N20; n =10). The experiment lasted 156 d and was divided into two periods. The first period lasted 140 d and consisted of the daily supply of narasin. In the second period (last 16 d), the animals were not supplemented with narasin when the residual effect of the additive was evaluated. The treatments were evaluated by linear and quadratic orthogonal contrasts. The results were reported as least square means and the effect was considered significant when P ≤ 0.05. No treatment × day interaction was identified for dry matter intake (P = 0.27). There was a treatment × day (P ≤ 0.03) interaction after narasin removal for the molar proportion of acetate, propionate, ac:prop ratio, and ammonia nitrogen. The inclusion of narasin decreased linearly (P < 0.01) the molar proportion of acetate (P < 0.01), and this effect persisted until day 5 after narasin withdrawal (P < 0.01). Narasin inclusion linearly increased the molar proportion of propionate (P < 0.04), and linearly decreased (P < 0.01) ac:prop ratio up to 5 d after removing narasin from the diets. No treatment effects were observed (P > 0.45) on days 8 and 16 after the withdrawal. Narasin linearly decreased ammonia nitrogen up to 1 day after withdrawal (P < 0.01). In conclusion, the use of narasin for a prolonged period (140 d) resulted in a residual effect on rumen fermentation parameters after the removal of the additive from the diets.

Keywords: additive; ionophores; ruminal parameters; washout.