MATERIALS AND METHODS

Study area: The field trial of the current study was carried out at Sheep and Goats Unit, Agriculture Experimental and Research Station, Faculty of Agriculture, Cairo University through the period from January to Mach, 2019. While the lab analysis extended to August 2020.

Ethical approval: The protocol of the present study was accepted by the Institutional Animal Care and Use Committee, Cairo University (IACUC) (Approval No. CU/II/F/22/21).

Thyme leaves and essential oils: Thyme (Thymus vulgaris) leaves were obtained from Beni Mazar districts, Minia Governorate, Egypt. The fresh leaves were dried at shadow till drying, then it was saved in polyethylene bags. A hydro distillation method by Clevenger type apparatus was used to extract the essential oil from fresh thyme leaves as described by Vakili et al.¹⁴. Then the collected oil was dehydrated by using anhydrous sodium sulfate. Oil percentage was calculated (1.65%) and stored in the fridge until using. The bioactive components in the thyme oil were determined by Gas Chromatography-Mass Spectrometry (GC-MS) instrument (a trace GC Ultra Gas Chromatographs (THERMO Scientific Corp., USA), coupled with a THERMO mass spectrometer detector (ISQ^™EC Single Quadrupole Mass Spectrometer) at the Department of Medicinal and Aromatic Plants Research, National Research Center.

Thyme in the current study contained 42.70% Thymol, 2.93% Carvacrol, 17.41% p-Cymene, 15.62% γ-Terpinene, 4.25% α-Terpinene, 1.65% Myrcene, 2.01% Linalool, 3.30% α-Pinene, 1.91% β-Pinene, 3.72% β-Caryophyllene and 4.50% Limonene.

Experimental animals and rations: Thirty-six multiparous lactating Damascus goats, 4 years old and an average weight 35 kg, after 7 days of parturition were divided into three groups (12 animals each) according to the milk production then, the experimental groups were randomly assigned to receive one of the experimental rations. The experiment lasted for 80 days (30 days adaptation period, milk yield was recorded 4 times with 2 weeks interval, then followed by 4 days for digestion trial and collection of rumen liquor and blood samples). Kids were separated from their mothers and changes in body weight of mothers and kids were determined biweekly.

Animals in the control group (C) were fed Egyptian clover (Trifolium alexandrinum) plus Concentrate Feed Mixture (CFM) without additives, while the other experimental animals were fed control ration plus 1% thyme leaves of total DM (G1) or the equivalent as thyme essential oil (G2). The equivalent amount of thyme essential oil was based on oil% in thyme which was 1.65%. All animal groups were offered rations at 3% of LBW (60% CFM: 40% Egyptian clover) to cover the total requirements recommended by NRC²⁰. Both thyme leaves (G1) and EO (G2) were mixed with a small amount of CFM daily just before feeding to ensure that animals consumed all amounts. The concentrate feed mixture consists of 68% yellow corn, 13% wheat bran, 17% soybean meal, 0.5% common salt and 1.5% limestone. The chemical compositions of the experimental ratio are shown in Table 1.

Feeding procedures: The concentrate feed mixtures and Egyptian clover were divided into two equal portions fed twice daily at 0800 and 1600 hrs. Freshwater was always available. Minerals blocks were available for all animals.

Milk sampling: Milk yield was recorded and milk samples were collected four times during the collection period for all animals by hand milking twice daily at 7 am and 5 pm. Whereas, one-tenth of the morning and the evening milk yields were mixed for each animal and stored at (-18°C) for further analysis.

Digestion trial and faeces sampling: After the collection period of milk, the digestion trial was performed using six animals from each group for three successive days using the bag technique to determine nutrient digestibility via the Acid Insoluble Ash (AIA) method as described by Lee and Hristov²¹. Nutrient’s digestibility was calculated according to the following formula:

A subsample (10%) of total collected faeces was sprayed with 10% sulfuric acid, then the drying process was done at 70°C for 24 hrs. The dried faeces were ground and stored for chemical analysis.

Rumen liquor sampling: Rumen liquor samples were collected at 0, 3 and 6 hrs. post-feeding by stomach tube from the six animals at the end of the faeces collection period. Samples were strained via two layers of cheesecloth, the ruminal liquor pH was determined immediately using a digital pH meter. Rumen fluid samples, after adding ortho-phosphoric acid, were stored using glass bottles at deep freeze (-18°C), then used for the analysis of Total Volatile Fatty Acids (TVFA’s) and Ammonia Nitrogen (NH₃-N).

Blood sampling: Blood samples were taken from the jugular vein from the six animals on the last day of the experimental period before the morning feeding in tubes containing Ethylene Diamine Tetra Acetic Acid (EDTA) as an anticoagulant. Blood plasma was obtained by centrifugation of the blood samples at 4000 rpm for 20 min and kept at deep freeze (-18°C) for further analysis.

Analytical procedures
Feeds and faeces analysis: Chemical analysis of feedstuffs and faeces samples was carried out according to AOAC²². The Nitrogen Free Extract (NFE) was calculated by difference. Fibre fractions were determined in feeds and faeces according to Van Soest et al.²³.

Rumen liquor analysis: Values of rumen pH were determined using Hanna digital pH meter. The concentration of Ammonia-Nitrogen (NH₃-N) in the rumen liquor was determined by the Kjeldahl distillation method²². Rumen total volatile fatty acids were estimated by steam distillation method as recommended by Wang et al.²⁴.

Blood plasma analysis: Blood plasma total protein and creatinine were measured as mentioned by Tietz²⁵. Blood plasma albumin was determined by the method of Doumas et al.²⁶. Blood plasma urea, alanine aminotransferase (ALT), aspartate aminotransferase (AST), total triglycerides, total cholesterol and glucose were estimated according to Reed²⁷.

Milk analysis: Total solids, fat, protein and lactose of milk samples were analyzed by infrared spectrophotometer (Foss Matic 120 Milko-Scan, Foss Q3 183 Electric, Hillerød, Denmark) as described by AOAC²². Solids not fat content of milk was calculated by the difference between total solids and fat content. Milk fatty acids profile was determined via High-Pressure Liquid Chromatography (HPLC) according to AOAC²⁸.

Statistical analysis: The general linear model procedure of SAS²⁹ was used for data analysis. Data of nutrients digestibility, blood and milk were analyzed using one way ANOVA procedure by following the next model:

Where:

While two-way ANOVA procedure was used to analyse the data of pH, NH3-N and TVFA according to the following model:

Where:

The differences among means were separated according to Duncan’s New Multiple Range Test.

RESULTS AND DISCUSSION

Nutrient’s digestibility and nutritive value: Data concerns nutrients digestibility and nutritive value in Table 2 indicated significant increases (p<0.05) in digestibility of DM (73.09 and 72.14%), OM (76.10 and 74.62%) and CP (72.59 and 73.39%) with G1 and G2, respectively compared with C (70.48, 73.75 and 70.69%), in the same order. Mirzaei-Aghsaghali et al.⁸ explained the digestion improvement with thyme EO addition by the positive effect of herbs and spices and their active compounds on activation of ruminal bacteria that are involved in the digestion process or by stimulation the secretion of bile salt, saliva or other digestive enzymes¹⁹.

Also, this improvement could be due to the anti-microbial properties of the main active components identified in the thyme EO such as thymol, carvacrol, pinene, p-cymene and limonene, which inhibit some microbial activity and stimulate the digestion process^30,31.

In the same trend, El-Naggar et al.¹⁶ and Ebrahimi et al.¹³ reported increases in DM and OM digestibility when thyme EO was added to lambs or calves’ rations, respectively. The same result was obtained by Mehrabadi et al.³² with in vitro DM and OM degradability when thyme leaves were added by 5, 10 and 15% of concentrate DM. However, in other studies, neither addition of thyme leaves³³ nor thyme EO^15,19 had a significant effect on DM and OM digestibility. In the same context, no significant effect of thyme EO was detected on in vitro DM³⁴ or OM degradability³⁵. The variations in the digestibility results with EO addition could be attributed to many factors such as dose, chemical composition, source of plant, extraction procedures of EO¹⁴.

The improvement in CP digestibility may be due to the anti-microbial effect of some phenolic compounds in EO such as thymol, which can modulate the microbial population in the rumen, which reduce the degradation of dietary protein, increases N escape and increase the protein flow to the lower gut, which result in improvement of nitrogen utilization^33,36.

In the same trend, significant^16,33 or insignificant increases¹⁹ were recorded in CP digestibility either with thyme leaves or EO addition.

In contrast, a significant reduction in CF digestibility was observed with thyme addition especially with EO being 61.56% compared with control being 65.89%. The same result was obtained with NDF digestibility, with no significant effect on ADF digestibility because of thyme addition. The NDF digestibility was reduced by 3.6 and 4.7% with G1 and G2, respectively. The decrease in CF and fibre fraction digestibility may be attributed to the sensitivity of fibrolytic bacteria to phenolic compounds as thymol found in thyme EO³⁴. Also, Cieslak et al.³⁷ indicated that, thymol may inhibit the growth of certain microorganisms in the rumen, which affects proteolysis and reduce fibre degradation.

In agreement with the previous results, Benchaar et al.³⁴ noted a significant decrease in vitro disappearance of NDF with thyme EO supply. The same results in CF and NDF digestibility were conducted by El-Essawy et al.¹⁹ when ewes’ ration supplemented with thyme EO, with no significant effect on ADF digestibility. On the other hand, increases in digestibility of CF¹⁶, NDF and ADF¹³ were reported with thyme EO supply. While Khattab et al.³⁸ observed no significant effect of thyme leaves addition on in vitro disappearance of NDF and ADF.

The highest TDN value (72.18%) was recorded with thyme leaves addition (G1), with no significant difference between G1 and G2 (70.77%). This improvement may be due to the increase in DM and OM digestibility with G1 and G2. Although DCP value was not significantly affected by thyme addition, there was an improvement especially with EO supply because of digestibility improvement of CP. The DCP values were 10.03, 10.30 and 10.41% for C, G1 and G2, respectively.

In agreement with our findings, TDN and DCP values were improved either with thyme leaves³³ or EO addition^16,19.

Rumen liquor parameters: Table 3 indicated no significant (p<0.05) effect of sampling time or thyme supplementation either in form of leaves or essential oil on rumen fermentation parameters. The lack of significant effect of essential oils on fermentation characteristics may be explained by the results of McIntosh et al.³⁹ that the active EO dose that can affect ruminal bacteria ranges from 35-360 mg L^–1, which cannot be achieved by in vivo trial. Also, Cardozo et al.⁴⁰ and Busquet et al.⁴¹ reported many factors that may eliminate the effect of EO on rumen parameters such as inadequate dose, concentrate to roughage ratio and adaption time, as longer adaption time will result in more adaption of rumen microorganisms to EO.

The mean values of ruminal pH ranged from 6.25 for C and G1 to 6.28 for G2. Matching with our results, neither thyme leaves addition^17,36,38, nor essential oil^14,16,19 had a significant effect on ruminal pH value. However, Benchaar et al.³⁴ recorded a significant increase in vitro pH value with thyme EO supply.

Current data showed insignificant decreases in NH3-N concentrations either at 3 (26.73 and 26.12 mg/100 mL) and 6 hrs (24.65 and 24.04 mg/100 mL) post-feeding or the mean value (24.96 and 24.63 mg/100 mL) with thyme addition (G1 and G2), respectively compared with control (29.66, 25.28 and 26.17, in the same order). Molero et al.⁴² indicated that, the active components in EO including thymol may reduce proteolysis and degradation of amino acids in the rumen because of reduction either inactivity of ammonia producing bacteria or preventing their growth³⁹. The major mode of action of these active components in herbal plants was suggested by their reduction effect on adhesion sites of ruminal bacteria to feed particles, which reduce the deamination process and NH3 production^5,36. In the same context, Evans and Martin⁴³ noted that thymol may affect the energy metabolism of Selenomonas ruminantium and Streptococcus bovis, the major deamination bacteria in the rumen.

Patra and Yu⁴⁴ showed that reducing the deamination of amino acids in the rumen may alter the digestion site of protein to the intestine. In the same line, Bodas et al.⁴⁵ reported that the decreases in vitro CP disappearance and NH3-N concentration may lead to an increase in the passage of dietary protein to the intestine and improve the nitrogen utilization by ruminants.

In the same trend, significant^16,17,35,46 and insignificant^19,32,38 decreases in the ruminal concentration of NH₃-N were reported with thyme addition. However, Benchaar et al.³⁴, Vakili et al.¹⁴, Ahmed et al.⁴⁷ and Ribeiro et al.¹⁵ recorded no significant effect.

Although the ruminal concentration of Total Volatile Fatty Acids (TVFA’s) was not affected by thyme supplementation, there were insignificant decreases with G1 and G2 being 9.04 and 9.06 mL eq/100 mL compared with control being 9.68 mL eq/100 mL. Castillejos et al.⁴⁸ suggested that, the reduction in TVFAʼs concentration with EO supply may be due to the anti-microbial effect of thymol, which inhibits rumen microorganisms and fermentation process. This anti-microbial activity of thymol may be attributed to the hydroxyl group in its structure, which reduce the membrane integrity of bacterial cells and reduce glucose uptake^49-51.

Also, a reduction in vitro TVFAʼs concentration was observed when thyme EO was added by 30, 300 and 600 ppm³⁵ or 100 mL L^{–1 46}. On the other hand, TVFA’s concentrations were not significantly changed with thyme leaves or EO supply in many studies^14,19,32,34.

Blood parameters: However, Table 4 showed no significant differences among groups in blood concentrations of Total Protein (TP), Albumin (ALB) and Globulin (GLO), there were enhancement in TP (7.35 and 7.39 g dL^–1) and ALB (4.27 and 4.36 g dL^–1) values with thyme addition (G1 and G2), respectively compared to 6.93 and 3.81 g dL^–1 in control. This result may be attributed to the improvement in CP digestibility with thyme groups.

In the same trend, no significant effect was detected in blood TP, ALB with the addition of either thyme EO¹⁹ or thyme leaves¹⁷. Also, Ebrahimi et al.¹³ did not find a significant difference in serum TP among dairy calves supplemented either with 1- or 2-ml thyme oil and control group. In contrast, Soltan⁵² recorded increases in blood TP concentration with EO supplementation at a level of 187 or 281 mg/day.

In the current study, there were decreases (p<0.05) in concentrations of Blood Urea Nitrogen (BUN) with thyme leaves (G1) being 22.36 mg dL^–1 or EO (G2) supply being 21.09 mg dL^–1 compared with control being 24.25 mg dL^–1. The high correlation between BUN concentration and NH3-N concentration in the rumen^53,54, may explain the reduction in BUN concentration in the current study by the inhibition effect of EO on ruminal bacteria that is responsible for ammonia production such as Peptostreptococcus anaerobius and Clostridium astyklandy ¹¹.

This reduction in BUN concentration is in accordance with results obtained by El-Essawy et al.¹⁹, who recorded insignificant decreases in BUN concentration with the addition of thyme EO to ewes’ ration. On the other hand, Vakili et al.¹⁴, Biricik et al.⁵⁵ and Khamisabadi et al.¹⁷ found no significant effect. While Seirafy and Sobhanirad⁵⁶ reported a significant increase in BUN concentration when 5 mL/day thyme oil was added to Holstein suckling calves.

The present data indicated that blood creatinine and glucose concentrations were not affected by thyme addition. Also, Vakili et al.¹⁴ and Khamisabadi et al.¹⁷ agree with the previous result. However, a significant increase in glucose concentration was observed by Ebrahimi et al.¹³ with thyme EO supply.

Current results revealed that the highest (p<0.05) concentrations of AST and ALT were recoded with thyme EO addition (G2) being 88.24 and13.73 IU L^–1, with no significant difference between G1 (87.05 and 13.15 IU L^–1) and G2 compared with control (86.18 and 12.41 IU L^–1), in the same order.

In the same context, Seirafy and Sobhanirad⁵⁶ noted increases in AST and ALT concentrations with thyme EO supply. While in the opposite to current findings, no significant effect was detected by Vakili et al.¹⁴, Khamisabadi et al.¹⁷ and El-Essawy et al.¹⁹.

The lowest (p<0.05) Concentrations of Total Cholesterol (CHOL) being 92.17 mg dL^–1 and Total Triglycerides (TRIG) being 15.14 mg dL^–1 were observed with thyme leaves-supplemented goats (G1), followed by those supplemented with thyme EO (G2) being 94.51 and 15.65 mg dL^–1 compared with the control group being 105.72 and 19.08 mg dL^–1, respectively. Michel et al.⁵⁷ explained these reductions in blood CHOL and TRIG concentrations by the hypolipidemic and hypercholesterolemia properties of aromatic plants and their EO. Also, it was indicated that the product of herbal plants metabolism may inhibit the production of the enzyme (3-hydroxy-3-methylglutaryl CO. A) that controls the cholesterol synthesis⁵⁸.

In matching with our results, Morsy et al.⁵⁹, Khamisabadi et al.¹⁷, Seirafy and Sobhanirad⁵⁶ and El-Essawy et al.¹⁹ reported decreases in blood CHOL and TRIG concentrations with thyme leaves or EO addition. In contrast, concentrations of CHOL and TRIG were not affected by the addition of thyme EO in the study conducted by Vakili et al.¹⁴.

Milk yield, composition and feed efficiency: Data of Dry Matter Intake (DMI), milk yield and composition, feed efficiency in Table 5 showed an insignificant (p<0.05) increase in DMI with thyme leaves supplementation (1215 g/day), while DMI tended to be decreased insignificantly (p<0.05) with thyme EO supply (1135 g/day) compared with control (1175 g/day). The depression in total DMI with EO supply may have resulted from palatability problems, which require an encapsulation of EO to overcome that problem⁵. Moreover, Ribeiro et al.¹⁵ cleared that mainly composed of EO may be affected by sensory properties such as odour, flavour and acceptability.

In the same trend, Khamisabadi et al.¹⁷ recorded an increase in DMI when lambsʼ ration was supplemented with thyme leaves. While decreases in DMI were observed with blend EO addition to dairy cows’ ration^6,60,61. In contrast, Seirafy and Sobhanirad⁵⁶ reported an increase in total DMI with thyme EO addition to Holstein suckling calves. However, no effect of thyme leaves or EO addition on DMI was detected by Vakili et al.¹⁴, El-Naggar et al.¹⁶, Mohamed et al.³³, Ebrahimi et al.¹³, El-Essawy et al.¹⁹ and Ribeiro et al.¹⁵. The variation in DMI with EO supply may be attributed to many factors such as EO source, diet type, the adaption of rumen microbes to EO^3,62. Furthermore, the chemical and physical characteristics of the diet can affect DMI^3,63.

In the current study, the highest (p<0.05) milk and 4% Fat Corrected Milk (FCM) yields were observed with thyme leaves addition (G1) being 1170 and 1133 g/h/day, respectively, with no significant difference between G1 and G2 (1125 and 1059 g/h/day) compared with control (935 and 939 g/h/day), in the same order. The increase in milk yield with thyme addition maybe because of the improvement in DM and OM digestibility. In this context, many theories explain the increase in milk production with thyme addition. One of these theories indicated that the increase in milk production with EO supply may be attributed to the change of ruminal fermentation pattern, through reducing acetate: Propionate ratio^5,64 or due to reduction in methane production¹¹.

Also, it may be because of stimulating endocrine glands in animals to release some hormones such as growth hormone⁶⁵, which stimulate milk production by elevating the conversion rate of feed nutrients into milk⁶⁶. Furthermore, the antioxidant property of the thymol may inhibit the lipid peroxidation of the free radicals, which protect the mammary secretory cells and keep them healthy⁶⁷ which lead to more milk production.

In parallel to the previous results, Mohamed et al.³³ recorded significant increases in milk and FCM yields when dairy goats fed ration supplemented with thyme leaves. Also, higher milk yield was recorded with EO addition to rations of dairy cows^61,68 or Chios dairy ewes⁷. Furthermore, Smeti et al.⁶⁹ demonstrated higher milk yield with goats supplemented with rosemary leaves than those supplemented with rosemary EO. On the other hand, EO addition had no significant effect on milk yield of lactating goats⁵⁹, lactating ewes¹⁹ and dairy cows^6,60,70,71.

Although milk composition was not affected either by thyme leaves or EO supplementation, there were insignificant decreases in fat contents (3.79 and 3.61%) and increases in protein contents (3.51 and 3.60%) with thyme (G1 and G2), respectively compared to 4.03 and 3.26% for control, in the same order. The previous result could be a reflection of the decrease in CF and the increase in CP digestibility (Table 2) and the improvement in blood total protein (Table 4) with thyme addition. Moreover, the reduction in NH₃-N concentration in the rumen (Table 3) may be an indicator of improving the synthesis of microbial protein, which reflects on higher milk protein content⁶³.

In matching with current findings, Mohamed et al.³³ and El-Essawy et al.¹⁹ found that milk fat content was decreased with thyme leaves or EO supply. Also, in coincidence with present results, Morsy et al.⁵⁹ and El-Essawy et al.¹⁹ reported an increase in milk protein with EO addition. On contrary, no change in milk fat content^60,61 and protein content^6,71 was detected with EO supply. However, Giannenas et al.⁷ and Flores et al.⁷⁰ did not record any effect of EO addition on milk composition.

Feed efficiency (milk yield, g/DMI, g) was significantly (p<0.05) improved with thyme leaves and EO addition by 20 and 24%, respectively compared with control.

In agreement with our data, feed efficiency was improved by 16.2% when dairy goats fed ration supplemented with thyme leaves³³. Also, it was reported that the supplementation of blend EO improved feed efficiency of Chios dairy ewes⁷ and dairy cows^61,68,71. However, El-Essawy et al.¹⁹ found that the addition of thyme EO to ration of lactating ewes did not affect feed efficiency.

Milk fatty acids profile: The milk fatty acids profile in Table 6 indicated significant and insignificant decreases in C6:0 to C15:1, C17:0, C18:0 and 20:0 with thyme addition. However, C16:0, C16:1 and C18:1 to C18:3 were increased with both thyme leaves and EO supply. As a coincidence to the previous results, concentrations of Total Saturated Fatty Acids (TSFA) were decreased (69.55 and 69.52%), while concentrations of Total Unsaturated Fatty Acids (TUFA) being (30.45 and 30.48%) and Total Poly Unsaturated Fatty Acids (TPUFA) being (2.99 and 2.98%) were increased either with thyme leaves or EO addition, respectively compared with control being 71.62, 28.38 and 2.70%, in the same order.

The decrease in TSFA and the increase in TUFA of milk with thyme supplementation may be attributed to the high anti-microbial properties of some phenolic compounds in thyme such as thymol, eugenol and carvacrol, because of the hydroxyl group in their structure^49,72 which negatively affect both gram-negative and gram-positive bacteria⁷³ via disturbance in the cytoplasmic membrane¹⁰. These compounds can inhibit the rumen microorganisms such as bacteria⁷⁴, which are involved in the biohydrogenation process of unsaturated fatty acids in the rumen³³. Furthermore, Tholstrup et al.⁷⁵ indicated that, the reduction in saturated fatty acids is correlated with less blood cholesterol, as reported in the present study (Table 4), which is considered as an indicator for more quality and healthy milk to consumers.

In the same trend, milk fatty acids profile either of lactating goats or ewes was improved because of EO supply^19,59 or due to thyme leaves addition³³.

Kids’ performance: Table 7 revealed no significant difference in birth Body Weight (BW) of kids among different groups. The average values of birth BW were 3.07 kg for C, 3.22 kg for G1 and 3.60 kg for G2. However, final BW (11.58 and 11.22 kg), total BW gain (8.36 and 7.62 kg) and Average Daily Gain (ADG) (111.47 and 101.61 g) were significantly (p<0.05) increased for kids of G1 and G2, respectively compared with those of control group being 9.32 kg, 6.25 kg and 83.33 g, in the same order. These results may be attributed to the improvement in energy metabolism with thyme addition because of the thymol effect on decreasing acetate and decreasing propionate production without affecting total VFA³³. Furthermore, residues of EO in milk may improve the appetite and weight of kids due to the digestion stimulant, antioxidant and antiseptic properties of thymol¹⁹. Moreover, a positive correlation between the growth rate of kids and milk production of mothers was reported by Smeti et al.⁶⁹, which matches with higher milk production with thyme addition in the current study.

In the same context, significant increases in final BW and ADG of kids and lambs were observed either with dairy goats supplemented with thyme leaves³³ or with lactating ewes supplemented with thyme EO¹⁹, in the same order. Moreover, Smeti et al.⁶⁹ demonstrated that kids of dairy goats who received rosemary leaves had higher final BW and ADG than those who received rosemary EO.

CONCLUSION

It could be concluded that both thyme forms (leaves or EO) improved digestibility and lactation performance of Damascus goats with no significant difference between the two forms. However, the supplementation of lactating goat's ration especially with thyme leaves recorded the best values of DM and OM digestibility, TDN and kids’ growth rate, the lowest concentrations of blood total cholesterol and triglycerides and the highest milk production with more healthy aspects for consumers.

SIGNIFICANCE STATEMENT

This study discovered that incorporating thyme (Thymus vulgaris) especially in form of leaves could be used successfully as a natural feed additive that can be beneficial for lactating goats’ performance. Furthermore, it has the potential to produce functional milk with a low concentration of total saturated fatty acids and a high concentration of total unsaturated fatty acids. This study will help the researchers to investigate more natural alternatives for antibiotics.