Effects of Bacillus licheniformis fermentation extract fed alone or with monensin on production performance and feed efficiency of dairy cows.

Increasing ruminal propionate relative to acetate production and alleviating excessive proteolysis are viable strategies for improving efficiency and can be achieved through supplementation of the ionophore monensin. In addition to monensin, other rumen modifiers, such as direct-fed bacteria or extracts derived from bacteria, have been introduced, and there is a need to determine how these additives interact with monensin. Supplementation of direct-fed Bacillus licheniformis has been demonstrated to enhance microbial protein synthesis in both sheep and dairy cows. The different responses of monensin and Bacillus licheniformis suggest a potential to improve feed efficiency additively when they are fed together. Thus, it was hypothesized by the authors cited that feeding both Bacillus licheniformis and monensin would result in greater improvement in feed efficiency than feeding either alone in lactating dairy cows. The study objective was to investigate the effect of monensin and a novel Bacillus licheniformis –derived fermentation extract (BLFE), predominantly containing exogenous enzymes that can improve starch and non-structural carbohydrate digestion, fed alone or in combination, on production performance and feed efficiency in lactating dairy cows. Additionally, the study aimed to assess the related changes in nutrient digestibility, blood metabolites, and ruminal and post-ruminal fermentation profiles.

Sixty Holstein cows matched for days in milk (108 ± 35 days) and lactation number were assigned to four treatments formulated to provide two doses of monensin (0 and 17.6 mg/kg DM) and two doses of BLFE (0 and 166 mg/kg DM) in a 2 × 2 factorial arrangement. Monensin and BLFE doses were top-dressed on a total mixed ration (TMR) without added monensin. Cows were allowed to adapt to treatments for 21 days before measuring dry matter intake (DMI), milk yield, milk composition, and body weight (BW) responses to treatments over the next 42 days. Rumen fluid volatile fatty acids (VFA), apparent total-tract digestibility (ATTD) of nutrients, and blood amino acid (AA) concentrations were determined in the last week.

Neither monensin nor BLFE modified DMI, which averaged 30.8 kg/day across treatments. At this DMI level, the actual monensin and BLFE doses consumed by cows were 14 and 145 mg/kg of DM, respectively. The BLFE fed alone increased milk yield: DMI (1.19 to 1.26) and nett energy for lactation (NEL): DMI (1.60 to 1.83). It also tended to increase milk yield and fat-corrected milk (FCM) and energy corrected milk (ECM) yields, DMI and milk protein yields, as well as crude protein (CP) intake. Supplementing BLFE with monensin attenuated those responses. Monensin fed alone increased BW gain (0.44 kg/day) and tended to increase the component-corrected milk yield: DMI, but supplementing it with BLFE negated those effects. Regardless of the presence or absence of monensin in the diet, BLFE increased milk protein content (3.45% to 3.52%), while monensin enhanced milk fat yield (95 g/day) and component-corrected milk yields (4.7% to 5.1%). Milk fat improvements from monensin were significant in multi-lactation cows but negligible in first-lactation cows. In contrast, the feed and protein efficiency enhancements of BLFE were more pronounced in first-lactation than in multi-lactation cows. Supplementing BLFE did not modify ruminal or faecal VFA profiles when supplemented alone or with monensin. However, monensin tended to decrease the molar percentage of butyrate in both rumen fluid and faeces, while the molar percentages of acetate and propionate, and their ratio remained unmodified. Supplementation with BLFE or monensin alone did not affect ATTD of CP, but supplementing both together increased ATTD of CP compared with supplementing BLFE alone (59.2% to 62.1%). The BLFE supplementation alone increased blood AA concentrations (18%), whereas adding monensin to the diet containing BLFE reversed that increase.

Conclusions: The results suggested that BLFE at 145 mg/kg DM and monensin at 14 mg/kg DM primarily acted independently rather than synergistically to enhance production performance and feed efficiency in lactating dairy cows. The BLFE and monensin distinctly enhanced milk protein and milk fat traits, respectively, under the current dietary conditions (high starch at ~30% and moderate CP of 15.4%). Both feed additives tended to enhance energy conversion efficiencies independently. While BLFE alone increased circulating amino acid concentrations and tended to improve the protein conversion efficiency, combining BLFE with monensin attenuated these effects, suggesting potential antagonism. The energy efficiency improvements of monensin were more prominent in multi-lactation cows, whereas the energy and protein efficiency improvements of BLFE were more pronounced in first-lactation cows. Further research, including varying doses of these feed additives and robust analyses of rumen function and nutrient metabolism, is needed to clarify their interactions, particularly those implying antagonistic effects.