Effect of narasin supplementation on performance of lambs fed high-forage diets

Abstract

Narasin is a feed additive used to alter ruminal fermentation and increase performance of cattle fed forage-based diets. The present study had two objectives: 1) to define the best dose of narasin for lambs fed forage-based diets; 2) evaluate whether the quality of the forage used can affect the action of narasin on performance of lambs. In Exp. 1, fifty-one crossbred ewe’s lambs [Dorper × Santa Inês; initial body weight (BW) = 25.9 ± 0.07 kg and 145 ± 2.1 d of age], were stratified by initial BW and randomly allotted in a tie-stall system in a randomized complete block design with 17 blocks and 3 treatments. The treatments for the 63-d feeding trial consisted of: 1) forage-based diet without narasin (CONT; n = 17), 2) CONT diet plus 13 ppm of narasin (13 N; n = 17), and 3) CONT diet plus 20 ppm of narasin (20 N; n = 17). Experimental diets were composed by 80 % of coastcross hay (Cynodon dactylon spp.) and 20 % of concentrate, which was used as delivery vehicle for the narasin treatments. Narasin inclusion increased (P < 0.01) dry matter and nutrients intake. There was a quadratic effect (P = 0.05) for average daily gain (ADG) and feed efficiency (FE), consequently, lambs fed diet containing 13 ppm of narasin had a greater (P = 0.05) final BW. In Exp. 2, fifty-two crossbred ewe’s lambs (Dorper × Santa Inês; initial BW = 25.63 ± 0.70 kg; age = 154 ± 2.6 d), were stratified by initial BW and randomly allocated in a tie-stall system in a randomized complete block design. The lambs were randomly assigned within blocks to 1 of 4 experimental diets in 2 × 2 factorial arrangements: different hay quality (Low CP = 70.5 g of CP/kg of DM; Medium CP = 118.0 g of CP/kg DM) and narasin inclusion (CONT = no narasin inclusion; 13N = diet plus 13 ppm of narasin. The experimental period lasted 84 days. There was no interaction (P > 0.49) among hay quality and narasin inclusion for any variable analyzed. Hay with high CP increased (P < 0.05) dry matter, ADG, FE, and final BW (P = 0.01) of the lambs. Narasin inclusion increased dry matter (P = 0.02) and nutrient intake. Moreover, lambs fed narasin had a greater (P < 0.05) ADG, FE, and final BW compared with control. The inclusion of 13 ppm of narasin improved performance of lambs fed with forage-based diets. The forage quality was determinant to lambs’ performance, and inclusion of 13 ppm of narasin was able to improve performance regardless of forage quality.