No abstract

The study aimed to evaluate if the frequency of narasin supplementation impacts dry matter intake, ruminal fermentation parameters, and apparent digestibility of nutrient in Nellore (Bos Indicus) steers fed forage-based diets. Thirty-two rumen-cannulated Nellore steers [initial body weight (BW) = 317 ± 27 kg; age =18 ± 1 mo] were assigned to individual pens in a randomized complete block design according to their initial shrunk BW. Within block, steers were randomly assigned to 1 of 4 treatments: 1) forage-based diet without the addition of narasin (CON; n = 8), 2) CON diet plus 13 ppm of narasin every 24 hours (N24; n = 8), 3) CON diet plus 26 ppm of narasin every 48 hours (N48; n = 8), or 4) CON diet plus 39 ppm of narasin every 72 hours (N72; n = 8). The experimental period lasted 30 d, with 18 d for diet adaptation and 12 d for sample collection. The experimental diets contained 95% of Tifton-85 (Cynodon dactylon spp.) haylage and 5% ground corn used as a delivery vehicle for narasin. Ruminal fluid was obtained from d 25 to 30 at 6 h after feeding to determine ruminal fermentation parameters. Narasin supplementation frequency did not affect (P ≥ 0.22) nutrient intake and total tract apparent digestibility. Steers fed N24 and N48 had reduced (P = 0.02) ruminal acetate concentration compared with CON and N72. Daily supply of narasin increased (P = 0.01) the molar proportion of propionate compared with CON and N72, and it did not differ between N24 vs. N48, N48 vs. N72, and N72 vs. CON. Also, N48 steers had greater (P = 0.01) rumen propionate concentration compared with CON. The N24 treatment decreased the Ac: Prop (P = 0.01) and AcBut: Prop (P = 0.02) ratio compared with CON and N72, while N48 had reduced (P = 0.01) Ac: Prop and AcBut: Prop ratio when compared with CON steers. Steers fed N24 and N48 had greater (P = 0.04) ruminal SCFA compared with CON, but it did not differ (P > 0.11) between N24, N48, and N72. Supplementing narasin to steers fed forage-based diets decreased (P < 0.01) ruminal ammonia concentration compared with CON steers regardless of supplementation frequency, being the least result observed for N24 steers. Collectively, narasin supplementation frequency affected fermentation parameters without altering the nutrient intake and total tract apparent digestibility. Hence, decreasing frequency of narasin supplementation to Nellore steers fed a forage-based diet did not reduce the capacity to modulate rumen fermentation parameters.

No abstract

Narasin is an antibacterial agent that may change rumen fermentation. Two experiments were proposed to evaluate the efficiency of narasin inclusion for lambs fed a diet containing high amounts of ground flint corn. Thirty rumen-cannulated wethers were used to evaluate nutrient digestibility, nitrogen balance, and rumen metabolism (Exp. 1); and forty-five lambs were used to evaluate performance (Exp. 2) of animals fed with narasin for high flint corn diets. The experimental diets were: control or basal diet without additives (C); 25 mg of monensin kg-1 of dry matter (DM) (M); and inclusion of 5 (N5), 10 (N10), and 15 (N15) mg of narasin kg-1 of DM. The statistical analyses were performed using the MIXED procedure of SAS. Monensin increased DM digestibility compared to C (p = 0.01) and increasing doses of narasin linearly increased DM digestibility (p < 0.01). There was a quadratic effect (p = 0.10) for molar proportion of acetate peaking at N15. Monensin inclusion increased (p = 0.07) propionate compared to C; however, it did not differ from narasin. The increasing levels of narasin linearly decreased the total volatile fatty acids concentration in the rumen (p = 0.02). Monensin and C showed a similar performance. The increasing levels of narasin linearly increased (p ≤ 0.04) average daily gain and feed efficiency. Monensin and narasin changed rumen fermentation and improved overall nutrient digestibility. However, lambs that received narasin showed improved performance when compared with animals that received M.