Effect of different levels of thyme extract on nitrogen retention, gas production, microbial population, protozoa and some blood parameters in fattening lambs and Kids

Low feed efficiency is one of the problems in the rumen of ruminants, which results in reduced growth and production of livestock and, most importantly, environmental pollution due to the release of methane and nitrogenous compounds . Changes in ruminal fermentation can be made to improve fermentation efficiency and substrate utilization and optimize feed nutritional value . Antibiotics have been successful in reducing energy loss (from methane) and protein (from ammonia nitrogen) in the rumen . However, today, due to general concerns about the remains of these compounds in milk and meat and thus increasing the bacterial resistance to them has caused the use of materials in feed as additive in some countries . Therefore, the tendency to find alternatives with natural origin for antibiotics has increased over recent years .Plant secondary metabolites are among the natural alternatives that have been studied in recent years that have antimicrobial properties.Essential oils, also known as volatile or ethereal oils, occur in edible, medicinal, andherbal plants. As these aromatic compounds are largely volatile, they are commonly extracted by steam distillation or solvent extraction . Essential oils can be extracted from many parts of a plant, including the leaves, flowers, stem, seeds, roots and bark. However, the composition of the EO can vary among different parts of the same plant . For instance, EO obtained from the seeds of coriander (Coriandrum sativum L.) have a different composition from the EO of cilantro, which is obtained from the immature leaves of the same plant . Chemical differences among EO extracted from individual plants, or different varieties of plants, also exist and are attributed to genetically determined properties, age of the plant, and the environment in which the plant grows . One of the plant essential oils that has a great potential for use in ruminant diets is the essential oil of thyme (Thymus Vulgaris). Thyme extract contains 0.6-8.8% (usually 1%) of essential oil, most of which are phenols (20-20%) and monoterpene hydrocarbons (such as P cymen and γ terpinen) and alcohols (such as Linalool and terpinen α). They show that sometimes these compounds make up 80% of the extract compounds. Naturally, thymol is also a major phenolic component in thyme and carvacrol is a sub – element (Leung and Foster., 1996). Although goats and sheep have often been fed and managed in a similar manner (goats being browsers and sheep being grazers), they are different, especially in their digestive capability, because of differences in the morphology of digestive system, including the mouth structure and gut, which may influence their ability to ingest and digest feed materials . Available information on efficiency of feed utilization between goat and sheep has been inconsistent with several studies reported sheep had higher growth performance than goats . In a recent in vitro study, Candyrine et al (2016) reported that goats had better rumen fermentation characteristics, including higher volatile fatty acids (VFAs) production and higher population of cellulolytic bacteria compared to sheep, suggesting that goats could be more superior in digesting feed materials.The results of studies performed on lambs and goats ) that have examined the effects of thyme extract or its major compounds (thymol and carvacrol) are very contradictory. And more research is needed to determine their effects on rumen fermentation and metabolism in lambs and goats. There is also little research on direct comparisons of the use of plant extracts in vivo between lambs and goats. Therefore, the aim of the present study was to compare these two species and the effects of thyme extract on performance and some ruminal parameters in fattening lambs and goat kids.The aim of this study was to investigate the effect of different levels of thyme (Thymus vulgaris) extract on growth performance, feed intake, daily weight gain and digestibility of nutrients in fattening lambs and kids. For this purpose, 15 goat kids (average initial BW of 17.3 ± 1.2 Kg, 3 month- old) and 15 Dalagh lambs (average initial BW of 21.4 ± 1.5 Kg, 3 month- old) were randomly assigned to 3 dietary treatments: 1) control (without thyme extract), 2) supplemented with 250 ml thyme extract and 3) supplemented with 500 ml thyme extract. Animals were kept in individual pens with self-mangers for 84 days. The results showed that there was no significant difference in nitrogen consumption through the use of extracts between different treatments. However, fecal and urinary excretion nitrogen was lower in treatments receiving 250 ml of thyme extract and retained and digested nitrogen was more than other treatments (P <0.01). Examination of interactions and species effects showed that the effect of thyme extract on excreted nitrogen and nitrogen retention in lambs was different from that of goat kids, so that excreted nitrogen was higher in goats and nitrogen retention was lower. With increasing levels of thyme extract, a significant decrease in gas and methane production was observed in both species (P <0.01). Rumen microbial population (total bacteria, coliforms and lactic acid bacteria) decreased due to the addition of thyme extract in both species, but this decrease was not significant. Also, in lambs and goats receiving thyme extract, with increasing the levels of the extract in the diet, the number of protozoa decreased significantly (P <0.01), so that the group receiving 500 ml of extract had the lowest number of protozoa. Concentrations of triglycerides, cholesterol, low-density lipoprotein and high-density lipoprotein were not affected by the use of the extract. However, blood glucose concentration increased significantly with increasing the extract in the diet and blood urea nitrogen concentration decreased (P <0.01). In general, the results of this study showed that the use of thyme extract in the diets of lambs and goats can significantly reduce gas production, especially methane gas and excretion of nitrogen through urine and feces, and thus increase nitrogen retention and digestion.