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

• Published in: Journal of animal science 2017-10, Vol.95 (10), p.4554-4567
• Main Authors: Crossland, W L, Tedeschi, L O, Callaway, T R, Miller, M D, Smith, W B, Cravey, M
• Format: Article
• Language: English
• Subjects: Acetic acid; Acid production; Animal Feed; Animals; Anti-Bacterial Agents - administration & dosage; Antibiotics; Bambermycins - administration & dosage; Cattle; Cattle - microbiology; Cattle - physiology; Diet; Diet - veterinary; Dietary Supplements; Fatty acids; Fatty Acids, Volatile - metabolism; Feed additives; Feeds; Fermentation; Food additives; Forage; Ionophores; Ionophores - administration & dosage; Male; Methane; Methane - metabolism; Methanogenesis; Microorganisms; Monensin; Monensin - administration & dosage; Propionic acid; Random Allocation; Rumen - metabolism; Rumen - microbiology
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas2017.1665

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.