Examining the effects of adding fat, ionophores, essential oils, and Megasphaera elsdenii on ruminal fermentation with methods in vitro and in vivo

摘要

Much attention has been drawn to the fatty acids (FA) present in the meat and milk from ruminant animals, which are often blamed for their high content of saturated FA, the intake of which is correlated with an increased risk of cardiovascular diseases in humans, and for the relatively low content of health promoting polyunsaturated FA (PUFA). Ruminal biohydrogenation (BH) can be manipulated to alter the amount of BH intermediates, such as PUFA, and decrease the flow of trans-10, cis-12 conjugated linoleic acid (CLA), which is an inhibitor for milk fat synthesis in dairy cattle. However, the BH of different FA in different feeds for ruminants is not fully understood in terms of microbes and metabolic processes related to BH. Methane mitigation and reducing the excretion of urinary N with dietary strategies are the major foci for ruminant nutritionists in terms of reducing the environmental impact of dairy operations. The combination of monensin and essential oil has been reported to surpress protozoa and methane production, while maintaining normal rumen function and minimizing the risk of metabolic diseases for cows in early lactation. A higher level of concentrate in the ration postpartum than prepartum places cows at high risk for rumen acidosis. Administration of the lactate utilizer, Megasphaera elsdenii, to ruminants has been suggested for reducing the incidence of acidosis.;In the first experiment, the objective was to determine the effects of raw and roasted soybeans, corn oil, soybean oil, and dried distillers grains with solubles (DDGS) and different particle sizes on the BH pattern of FA in vitro. Fat sources combined with grass hay were formulated to achieve 10% FA (dry matter basis; DMB) in each treatment. Incubation was maintained for 24 h in tubes, and fermentations of each treatment were stopped at 0, 1, 2, 4, 8, 12, 16 and 24 h. The fractional rates of disappearance of 18:2 and 18:3 were estimated by a single pool, first-order kinetic model. The BH differed with fat sources. Overall, DDGS had the highest BH among the treatments. Roasted soybeans, corn oil, and soybean oil had similar BH, which were lower compared with DDGS. Roasting and particle size did not affect overall BH. However, the roasting process and particle size affected the rate of disappearance of 18:2 in soybeans. Particle size exerted minimum effect on BH, but the particle sizes differed at most by 1 mm in this study.;The second experiment was conducted in a modified dual flow continuous culture system. The objective was to determine the effects of feeding Rumensin RTM (ionophore with active component of monensin sodium) and Cinnagar RTM (essential oil of cinnamon and garlic) in diets on ruminal fermentation characteristics. Four continuous culture fermenters were maintained in 4 periods in a 4 X 4 Latin square design with 4 dietary treatments arranged in a 2 x 2 factorial: (1) control diet, 40 g of a 50:50 concentrate:forage diet containing no additive; (2) Rumensin at 11g/909 kg of DM; (3) Cinnagar at 0.0043% (DM basis); and (4) a combination of Rumensin and Cinnagar at the levels used in (2) and (3). Protozoa counts were used to calculate their generation times. A by-difference procedure involving boiling and sonication was developed to determine the protozoal N per cell to minimize feed contamination. There were no effects of treatment on protozoal generic distribution, concentration of NH3-N, total N flow of effluent, production of total VFA, and flows of CLA and total C18.;In summary, the one-stage incubation in vitro allowed us to assess the BH of certain FA sources in a closed system. BH in vitro can provide information to relate BH of FA in different fat sources in vivo. The continuous culture system, as a two-stage in vitro incubation, with retained diverse protozoal population allowed the study on ruminal fermentation characteristics under different dietary conditions in a controlled environment. Further research is needed on cell size change of ruminal protozoa upon the Cinnagar addition and how to inhibit protozoa enough to decrease their negative effects but not so much to disrupt normal microbial ecology of the rumen. The study of dosing M. elsdenii to dairy cows shed light on the potential benefit of this probiotic on the ruminal conditions and performance of dairy cows. The molecular techniques allowed us to monitor the establishment and persistence of M. elsdenii in the rumen. A greater number of cannulated cows are needed to better understand the change of population of M. elsdenii. (Abstract shortened by UMI.).