Document Type : Research Articles
Authors
Department of Animal Nutrition, Faculty of Animal Sciences and Fisheries, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran
10.22067/ijasr.2025.94142.1252
Abstract
Introduction and Objective: Buffers are commonly incorporated into high-concentrate diets to mitigate the adverse effects of ruminal acidity by stabilizing rumen pH. Their inclusion can increase the acetate-to-propionate ratio and improve fiber digestibility, ultimately enhancing feed intake. In parallel, plant extracts, owing to their antimicrobial, antioxidant, and biologically active properties, have emerged as promising feed additives. Among these, thyme extract has demonstrated antimicrobial activity under in vitro conditions, evidenced by reduced methane production and altered rumen fermentation characteristics. Garlic extract functions as a probiotic and possesses antioxidant, antimicrobial, anti-methanogenic, and anti-protozoal properties. Eucalyptus extract contains a mixture of volatile essential oils such as 1,8-cineole, limonene, and α-terpineol, along with non-volatile phenolic compounds, which may modulate rumen fermentation and inhibit methanogenesis. Given the potential benefits of both buffers and plant extracts, this study aimed to evaluate the effects of supplementing the diet with 2% sodium bicarbonate and plant extracts (thyme, garlic, and eucalyptus) on gas production parameters, ruminal degradability, and the apparent digestibility of nutrients.
Materials and methods: This study investigated the effects of 2% sodium bicarbonate combined with various plant extracts on in vitro gas production, ruminal degradability parameters of dry matter (DM), crude protein (CP), and neutral detergent fiber (NDF) using the in sacco method, as well as the apparent nutrient digestibility of the diet. The experimental treatments included: 1) 2% sodium bicarbonate (control); 2) Control + thyme extract (400 mg/kg DM of the diet); 3) Control + garlic extract (300 mg/kg DM of the diet); 4) Control + eucalyptus extract (150 mg/kg DM of the diet). A fattening lamb diet was formulated using SRNS software and offered as a total mixed ration (TMR) consisting of forage and concentrate at a 30:70 ratio. To determine ruminal degradability parameters, three rumen-fistulated Zel ewes (average body weight: 43±2 kg; age: 2 years) were used. The animals were housed individually in semi-open, roofed metabolic cages with free access to water. Following an adaptation period to both the environment and a maintenance-level diet, they were fed slightly above maintenance requirements twice daily (at 08:00 and 20:00). Apparent nutrient digestibility was determined using the acid-insoluble ash (AIA) method as an internal marker. Data were analyzed using SAS statistical software, and treatment means were compared using Duncan’s multiple range test.
Results: The results indicated that gas production potential (P = 0.0003) and gas production at 96 hours (P = 0.0002) were significantly higher in the treatment containing eucalyptus extract compared to the other experimental treatments. Organic matter digestibility (P = 0.0352), metabolizable energy (P = 0.0371), and the concentration of short-chain volatile fatty acids (P = 0.0482) were significantly higher in the eucalyptus extract and control groups compared to the thyme extract treatment. The rapidly degradable fraction of DM was significantly increased in the eucalyptus extract treatment compared to the thyme and garlic extract treatments (P = 0.0137). The slowly degradable fraction and effective degradability of DM at outflow rates of 0.02, 0.05, and 0.08 showed a trend toward significance in the garlic extract treatment compared to the control group (P = 0.0828). The degradation rate constant of DM was significantly higher in the eucalyptus extract treatment compared to the other experimental groups (P = 0.0218). None of the ruminal degradability parameters for CP were significantly affected by the experimental treatments (P > 0.05). The rapidly degradable fraction of NDF was significantly reduced in all plant extract treatments compared to the control group (P = 0.0009), while no significant differences were observed among treatments for the other ruminal degradability parameters of NDF (P > 0.05). Dry matter digestibility (P = 0.0155) and organic matter digestibility (P = 0.0041) were significantly increased in all plant extract treatments compared to the control. The effect of treatments on crude protein digestibility showed a trend toward significance (P = 0.0874). Neutral detergent fiber digestibility was significantly higher in the thyme extract treatment compared to the other treatments (P = 0.0200). Finally, crude fat digestibility was significantly increased in all plant extract treatments compared to the control group (P = 0.0406).
Conclusion: The results of the gas production assay indicated that gas volume was influenced by the experimental treatments and was reduced with the inclusion of plant extracts (particularly thyme and garlic) which may be attributed to the antimicrobial effects of the extracts on rumen bacteria. Overall, the use of sodium bicarbonate and plant extracts in the diet had no adverse effects on gas production or ruminal degradability parameters and led to an improvement in the apparent digestibility of dietary nutrients.
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