Effects of rotating antibiotic and ionophore feed additives on volatile fatty acid production, potential for methane production, and microbial populations of steers consuming a moderate-forage diet

Abstract

Ionophores and antibiotics have been shown to decrease ruminal methanogenesis both in vitro and in vivo but have shown little evidence toward a sustainable means of mitigation. Feed additive rotation was proposed and investigated for methane, VFA, and microbial population response. In the present study, cannulated steers ( = 12) were fed a moderate-forage basal diet in a Calan gate facility for 13 wk. In addition to the basal diet, steers were randomly assigned to 1 of 6 treatments: 1) control, no additive; 2) bambermycin, 20 mg bambermycin/d; 3) monensin, 200 mg monensin/d; 4) the basal diet + weekly rotation of bambermycin and monensin treatments (B7M); 5) the basal diet + rotation of bambermycin and monensin treatments every 14 d (B14M); and 6) the basal diet + rotation of bambermycin and monensin treatments every 21 d (B21M). Steers were blocked by weight in a randomized complete block design where the week was the repeated measure. Rumen fluid was collected weekly for analysis ( = 13), and results were normalized according to individual OM intake (OMI; kg/d). Potential activity of methane production was not significantly different among treatments ( > 0.05). However, treatment tended to affect the CH-to-propionate ratio ( = 0.0565), which was highest in the control and lowest in the monensin, B21M, and B14M treatments (0.42 vs. 0.36, 0.36, and 0.33, respectively). The CH:propionate ratio was lowest in wk 2 and 3 ( < 0.05) but the ratio in wk 4 to 12 was not different from the ratio in wk 0. Week also affected total VFA, with total VFA peaking at wk 3 and plummeting at wk 4 (4.02 vs. 2.86 m/kg OMI; < 0.05). A significant treatment × week interaction was observed for the acetate-to-propionate (A:P) ratio, where bambermycin- and rotationally fed steers did not have a reduced A:P ratio compared with monensin-fed steers throughout the feeding period ( < 0.0001). Microbial analysis revealed significant shifts, but several predominant classes showed adaptation between 4 and 6 wk after additive initiation. There was no significant evidence to suggest that rotations of monensin and bambermycin provided additional benefits to steers consuming a moderate-forage diet at the microbial/animal and environmental level versus those continuously fed.

>b<Long-term use of narasin, salinomycin and flavomycin for Nellore steers fed with high-forage diets:>/b< ruminal parameters, apparent nutrient digestibility, and performance

“…Supporting our results, others have also reported increased concentration of rumen propionate and total VFA, and reduced concentration of rumen acetate and butyrate when narasin was fed to beef cattle (Miszura et al, 2018;Polizel et al, 2020). Also corroborating with this study, flavomycin (Mogentale et al, 2010;Crossland et al, 2017) or salinomycin (Olumeyan et al, 1986;Zinn, 1986) supplementation to beef cattle consuming or not a forage-based diets was not capable of changing ruminal fermentation parameters. In fact, Olumeyan et al (1986) and Zinn (1986) reported that rumen fermentation only changed when the diets had increased amount of grain.…”

“…Supporting this statement, Bell et al (2017) and Polizel et al (2020) also reported similar rumen pH values of beef steers offered a high forage-based diets with monensin and narasin, respectively. Accordingly, Crossland et al (2017) did not observe any effect of flavomycin or monensin supplementation on rumen pH of beef steers offered a moderate forage-based diet. In fact, the ruminal pH in the present study was within a range that supports and maintains adequate fiber digestion in ruminants (Yokoyama and Johnson, 1988).…”

“…Corroborating with our results, Kobayashi et al (1992) reported no differences in apparent digestibility of nutrients in wethers supplemented with salinomycin. Crossland et al (2017), however, observed that flavomycin or monensin supplementation decreased dry matter digestibility from week 1 to 3 and increased at…”

“…It is still controversy in the literature the impacts of ionophores and nonionophores on nutrient digestibility (Wedegaertner and Johnson, 1983;Ricke et al, 1984;Crossland et al, 2017;Polizel et al, 2020). In the current study, the inclusion of feed additives into forage-based diets did not impact apparent digestibility of nutrients (Exp.1).…”

“…In forage-based diets, data have shown the possible enhance of animals' performance when fed with flavomycin (Bretschneider et al, 2008). However, few trials were designed to study a long-term effect of this molecule, recently data create the hypothesis that the effect of flavomycin is punctual and not persistent caused by bacterial resistance or adaptation (Butaye et al, 2003;Crossland et al, 2017).…”