Effects of different levels of the savory essential oil on in vitro ruminal fermentation parameters, microbial protein synthesis and protozoal populations in two diets supplemented with fish and soybean oil

Despite the central importance of ruminants in providing the human nutritional requirements, their relatively low production efficiency leads often to increased production costs and pollut the environment. In this connection, using supplements and feed additives have considered as efficient strategies for improving the efficiency of livestock production. The plant-based feed additives, including essential oils and plant extracts, are the products that improve the efficiency of the ruminant production, through ameliorating the rumen digestion and fermentation. On the other hand, using the supplements, such as the different fat sources as the energetic supplement in animal diet, has had several positive impacts such as reducing ruminal acidosis, reducing methane production and and consequently declining environmental pollution, and improving feed energy efficiency and the performance of animals. Regarding the growing importance of high-quality products and special interest of consumers for the safety and quality of animal products in recent years, the feed additives of natural and green origin have been of great interest for animal nutritionists in recent decades. In this context, the current research aimed at investigating in vitro the savory essential oil effects on rumen fermentation, microbial protein synthesis and protozoal population in two diets supplemented with fish and soybean oils.

The essential oil was extracted by steam distillation using a clevenger apparatus, and was subsequently analysed qualitatively and quantitatively by Gas Chromatography-Mass Spectrometry (GC-MS). The essential oil effects on fermentation parameters were tested in vitro at 0, 150, 300, 450, and 600 mg/ in two diets supplemented with fish and soybean oils using the incubations of 24 h.

None of the rumen fermentation parameters was affected by the diet type. The gas produced over 24 h of incubation, in vitro true dry matter and organic matter degradability decreased linearly with increasing doses of the essential oil (P < 0.01) in both experimental diets. However, the partitioning factor as well as the microbial protein, and the efficiency of microbial protein synthesis increased none-linearly (linearly and quadratically) and linearly, respectively, with the essential oil dosage (P < 0.01). The ruminal ammonia concentration decreased none-linearly with the essential oil dosage (P < 0.01). Total protozoa numbers as well as most of the rumen common protozoal genera were reduced by increasing doses of the essential oil (P < 0.01). Total VFA concentration increased at the doses up to 450 and 300 mg/L of the essential oil in the fish oil and soybean oil containing diets, respectively (P < 0.05), and decreased thereafter at higher doses. The acetate molar proportions decreased none-linearly and that of propionate increased quadratically in both diets with essential oil dosage (P < 0.05).

In total, these findings indicated that using the savory essential oil, especially at low and medium doses, improved rumen fermentation through enhancing microbial protein synthesis, reducing ammonia and protozoa population, and increasing TVFA. Hence, the above-mentioned doses of the this essential oil can improve rumen fermtaion thereby enhancing the farm animals productivity. However, the savory essential oil seems to have negative impact on some rumen microorganisms at 450 mg/L and higher doses.