Effects of lasalocid, narasin, or virginiamycin supplementation on rumen parameters and performance of beef cattle fed forage-based diet.

Two experiments were designed to evaluate the impacts of supplementing lasalocid (LAS), narasin (NAR), or virginiamycin (VRM) on rumen fermentation parameters, apparent nutrient digestibility, and blood parameters (Exp. 1), as well as feed intake and performance (Exp. 2) of Nellore cattle consuming a forage-based diet. In Exp. 1, 32 rumen-fistulated Nellore steers (initial shrunk body weight [BW] = 355 ± 4.4 kg) were assigned to a randomized complete block design. Within block, animals were randomly assigned to one of four treatments: 1) forage-based diet without feed additives (CON), 2) CON diet plus 13 mg/kg of dry matter (DM) of NAR, 3) CON diet plus 20 mg/kg of DM of sodium LAS, or 4) CON diet plus 20 mg/kg of DM of VRM. No treatment effects were detected (P ≥ 0.32) for intake and apparent digestibility of nutrients. Steers fed NAR had the lowest (P ≤ 0.01) molar proportion of acetate on day 28, 56, and 112 vs. CON, LAS, and VRM steers, whereas acetate did not differ (P ≥ 0.25) between LAS, VRM, and CON steers from day 28 to 84. On day 112, steers fed LAS had a lower (P < 0.02) molar proportion of acetate vs. VRM and CON, whereas it did not differ between CON and VRM (P > 0.33). Steers receiving NAR had a greater (P ≤ 0.04) ruminal propionate vs. CON, LAS, and VRM, whereas LAS steers had greater (P < 0.04) propionate vs. CON and VRM steers on day 28 and 112, and it did not differ (P > 0.22) between CON and VRM. In Exp. 2, 160 Nellore bulls were blocked by initial shrunk BW (212 ± 3.1 kg) in a 140-d feedlot trial. Diets contained the same treatments used in Exp. 1. Bulls fed NAR had greater (P < 0.02) average daily gain (ADG) vs. CON and VRM, and similar (P = 0.17) ADG between NAR and LAS, whereas ADG did not differ (P > 0.28) between LAS, VRM, and CON bulls. A treatment effect was detected (P = 0.03) for dry matter intake, being greater in NAR vs. CON, LAS, and VRM bulls, and similar (P > 0.48) between CON, LAS, and VRM bulls. A tendency was detected (P = 0.09) for feed efficiency, which was greater (P < 0.02) in NAR bulls vs. CON and VRM, and similar (P = 0.36) between NAR and LAS bulls. From day 112 to 140, bulls receiving NAR were heavier (P < 0.03) vs. CON, LAS, and VRM bulls, but no differences were observed (P > 0.51) between CON, LAS, and VRM bulls. Collectively, ruminal fermentation profile and intake were impacted by NAR supplementation, which partially contributed to the enhanced performance of Nellore bulls receiving a forage-based diet.

Feed additives are nutritional tools that benefit dietary digestibility and nutrient utilization, alter ruminal fermentation routes, and improve cattle growth and efficiency, thus increasing productivity and profitability in beef cattle systems. Nonetheless, most of the current research focuses on supplementing feed additives in high-concentrate diets. Leaving a significant gap in understanding the influence of feed additives in cattle consuming forage-based diets, especially molecules capable of altering the fermentation process and, consequently, beef cattle performance. Therefore, this experiment aimed to evaluate the impacts of supplementing narasin (NAR), lasalocid (LAS), or virginiamycin (VRM) on rumen fermentation parameters, apparent nutrient digestibility, feed intake, and performance of Bos indicus Nellore cattle consuming a forage-based diet. Including commercially available feed additives into forage-based diets did not impact nutrient intake and digestibility of nutrients. The inclusion of NAR affected ruminal fermentation parameters toward propionate production, positively contributing to animal performance. Ruminal fermentation characteristics and animal growth were not impacted by dietary LAS and VRM, which could be attributed to the dose used in the current experiment, despite the manufacturer's recommendation. This research provides insights into NAR as an important feed additive for forage-based beef cattle diets.

Effects of narasin supplementation frequency on intake, ruminal fermentation parameters, and nutrient digestibility of Bos indicus Nellore steers fed with forage-based diets.

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. A total of 32 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 h (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 short-chain fatty acids 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.