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RESEARCH ARTICLE (Open Access)

Investigation of the relationship between meat fatty acids and the expression levels of genes associated with lipid metabolism in Kivircik and Hungarian Merino sheep

Fadime Daldaban https://orcid.org/0000-0001-5795-8859 A * , Hulya Yalcintan B , Pembe Dilara Kecici B , Bekir Ozturk C , Bulent Ekiz B , Bilal Akyuz A and Korhan Arslan A
+ Author Affiliations
- Author Affiliations

A Department of Genetics, Erciyes University, Kayseri 38280, Türkiye.

B Department of Animal Breeding and Husbandry, İstanbul University-Cerrahpaşa, Büyükçekmece, İstanbul 34500, Türkiye.

C Pınarhisar District Directorate of Agriculture and Forestry, Kırklareli 39300, Türkiye.


Handling Editor: Edward Clayton

Animal Production Science 65, AN25020 https://doi.org/10.1071/AN25020
Submitted: 20 January 2025  Accepted: 14 July 2025  Published: 4 August 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Depending on the degree of saturation, fatty acids can be saturated (SFA) or unsaturated (UFA: monounsaturated (MUFA) or polyunsaturated (PUFA) structures) and are of vital importance in energy production, metabolic processes, and structural activities in living organisms. Maintaining human health requires restricting the dietary intake of saturated fats while increasing the intake of UFAs. In this context, it is important for the livestock sector to develop animal improvement programs aimed at reducing the saturated fatty acid content and increasing the unsaturated fatty acid content of animal products.

Aim

This study aimed to investigate the expression levels of genes related to lipid metabolism (PPAR-α, PPAR-γ, PCK2, SCD, LEP, FABP4, and FASN) with SFAs, MUFAs, and PUFAs found in the longissimus dorsi muscle in the Kivircik and the Hungarian Merino lambs.

Methods

The study involved 10 Kivircik and 10 Hungarian Merino lambs, weaned at 90 days of age. After the lambs were slaughtered, tissue samples were taken from the longissimus dorsi muscle to be used for fatty acid and gene expression analyses.

Key results

The determining genes identified for the MUFAs included the LEP gene for all fatty acids, excluding C16:1, C17:1 and C18:1 in the Kivircik lambs; the SCD gene for C14:1 and the PPAR-γ gene for C22:1 in the Hungarian Merino lambs. The determining genes identified for the PUFAs included the LEP gene for the n-3 PUFAs in the Kivircik lambs and PPAR-α, PCK2, SCD, and LEP in the Hungarian Merino lambs.

Conclusions

This study suggests that the PPAR-α, PPAR-γ, PCK2, SCD, and LEP genes, all of which are involved in adipogenesis, are potential candidate genes for animal breeding programs aimed at modifying fatty acid profiles in ovine breeds. This suggestion is based on their expression levels being particularly correlated with UFA profiles.

Implications

In this study, the LEP gene, among the genes investigated offers potential for use in animal breeding programs aimed at MUFAs, n-3 PUFAs, and n-6 PUFAs. Given the impact of PUFAs, including omega-3 and omega-6, on human health, identification of genes correlated with specific fatty acids in this study is expected to contribute to the discovery of potential alternative therapeutic agents.

Keywords: animal breeding, fatty acids, human health, lamb, LEP, MUFAs, PPAR, PUFAs, therapeutic agent.

Introduction

Sheep represent an important alternative source of red meat, particularly in countries characterised by a steppe climate and low-quality grasslands (Arslan et al. 2022). Recently, consumer demand has shifted toward higher eating quality in red meat. In this context, intramuscular fat (IMF), which plays a key role in attributes such as juiciness, flavour, and tenderness, is recognised as a major determinant of meat-eating quality and a significant factor influencing consumer purchasing decisions (Pethick et al. 2021; Liu et al. 2021). As a critical meat quality parameter, marbleization is an important trait for all meat-producing farm animals, including sheep (Cheng et al. 2015). Marbling, which results from both hyperplasia and hypertrophy in intramuscular adipocytes, manifests as visible white flecks or streaks within the muscle fibres (Tan and Jiang 2024). Marbling, being the best indicator of homogenous IMF distribution, makes meat palatable, juicy, and tender (Ladeira et al. 2018).

In farm animals, IMF deposition, and the number and size of fat cells, which directly affect meat quality, are regulated by adipogenesis (Jin et al. 2022). Therefore, research on adipogenesis is significant for the improvement of meat-producing farm animals (Luo et al. 2023; Xu et al. 2023). Variations in gene expression related to specific fat tissues and differences in the expression levels of genes associated with various types of fat tissue may lead to variations in fatty acid concentrations and the number of fat cells. However, the molecular mechanisms underlying the differences observed among livestock breeds for the amount and composition of body fat are not yet fully understood (Bartoň et al. 2021). Nonetheless, given its capacity to influence meat yield and quality attributes in livestock, investigation of genes involved in adipogenesis and factors regulating the expression of these genes may contribute to clarifying this matter (Yang et al. 2015). Certain genes implicated in adipogenesis belong to the peroxisome proliferator-activated receptor (PPARs) gene family, which is integral to adipocyte development and the control of lipid metabolism in skeletal muscles (Xu et al. 2025). Peroxisome proliferator-activated receptor-gamma (PPAR-γ), a member of this family, functions as a transcription factor to induce gene expression, facilitating the differentiation of pre-adipocytes into mature adipocytes and the accumulation of IMF (Guo et al. 2024). Peroxisome proliferator-activated receptor-alpha (PPAR-α), another member of this family, plays a role in regulating proteins associated with fatty acid oxidation and extracellular lipid metabolism (Chen et al. 2018). The phosphoenolpyruvate carboxykinase 2 (PCK2) gene encodes the enzyme phosphoenolpyruvate carboxykinase 2, which acts as a regulator of fat deposition (Hanson and Reshef 2003). Stearoil–CoA desaturase (SCD) is the enzyme responsible for the conversion of saturated fatty acids into monounsaturated fatty acids (MUFAs) in mammalian adipocytes (Taniguchi et al. 2004). The hormone leptin (LEP), primarily secreted by white fat cells but also produced by various organs and tissues, including skeletal muscle, plays a key role in physiological mechanisms related to energy metabolism and fat deposition. Owing to these roles of leptin, the LEP gene is considered a potential candidate for improving carcass and meat quality traits in farm animals (Shin and Chung 2007). The fatty acid-binding protein 4 (FABP4), involved in fatty acid transport and lipolysis, also takes part in lipid metabolism (da Costa et al. 2013). Owing to its catalytic effect on fatty acid synthesis, fatty acid synthase (FASN) is described as an enzyme involved in body fat deposition and fatty acid composition (Roy et al. 2005).

The amount, composition, and distribution of IMF vary among livestock breeds (Bureš and Bartoň 2018). Additionally, the expression levels of genes involved in lipid metabolism vary among breeds and different types of fat tissue. The Hungarian Merino is a crossbred sheep breed well adapted to poor pastures and arid, hot climates. The development primarily focused on meat production, utilising Hungarian Merino, German Meat Merino, Rambouillet Merino, Russian Merino, and French Précoce breeds. In contrast, breeds such as Kent, Corriedale, Australian Merino, and Booroola Merino were utilised mainly to improve fleece yield (Loukovitis et al. 2023). Although the Hungarian Merino sheep breed is raised for dual-purpose production (meat and fleece), meat production is considered more important and economically profitable (Loukovitis et al. 2023). The Kıvırcık sheep, a native breed specific to Türkiye, is predominantly reared in the Thrace and South Marmara regions and accounts for approximately 6–7% of the national sheep population (Şengül and Çelik 2025). The Kıvırcık sheep breed, characterised by its thin-tailed structure, enhances overall meat quality by contributing to a balanced distribution of intramuscular and intermuscular fat. This characteristic plays a key role in the breed’s preferential use for meat production (Kader Esen et al. 2024).

The chemical composition of meat, particularly its fatty acid profile, makes a significant contribution to overall meat quality. Fatty acids are classified as saturated or unsaturated depending on their degree of saturation. Saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs), which include MUFAs and polyunsaturated fatty acids (PUFAs), have similar caloric values. However, SFAs are associated with increased fat deposition and bodyweight gain (Zhou et al. 2024). Therefore, it is recommended to limit the dietary intake of saturated fats to reduce the risk of developing cardiovascular disease (Panayotov 2021). In this context, improving the quality of sheep meat by decreasing the amount of saturated fat and increasing the amount of unsaturated fat in its composition could play a significant role in enhancing the overall nutritional value and consumer appeal of sheep meat (Junkuszew et al. 2020; Kang et al. 2025).

This study aimed to investigate the expression levels of the PPAR-α, PPAR-γ, PCK2, SCD, LEP, FABP4, and FASN genes, which are known to be involved in lipogenesis, in the longissimus dorsi (LD) muscle, alongside the fatty acid profiles of Kivircik lambs, a breed native to Türkiye known for its high meat quality, and Hungarian Merino lambs, an imported and improved breed.

Materials and methods

Animal material

This study was conducted at a private sheep farm located in the Kırklareli province of the Thrace region in Türkiye. All procedures applied to animals in the research comply with the criteria specified in the European Union (EU) Directive for animal experiments (European Union 2010) and the national regulation on the protection of animals used for experimental and other scientific purposes (Anonymous 2011). The experimental procedures of this study were approved by the Ethic Committee of Istanbul University-Cerrahpasa (Approval No: 2021/08 and Date: 17 January 2022). The study involved 20 male lambs, comprising Hungarian Merino (n = 10) and Kivircik (n = 10) breeds. The lambs were selected from healthy, weaned individuals, aged approximately 90 days, and within the reference breed-specific bodyweight range for their age group. After a 1-week acclimatisation period, the lambs were housed in a closed pen, divided into individual boxes providing an average of 1 m2 per animal. The boxes were uniform in size and equipped with identical feeders and waterers. Throughout the fattening period, the lambs were provided with ad libitum access to concentrate, roughage, and fresh, clean water.

At the end of the fattening period, the lambs were transported to a slaughterhouse and slaughtered according to standard abattoir procedures applied in Türkiye. Each hot carcass was assigned an individual number, and samples from the LD muscle, taken at the 12th−13th dorsal vertebrae level, were collected for genetic analysis. These samples were stored at −80°C until analysis. Additionally, further LD muscle samples were collected for fatty acid analysis. After aging at 4°C for 72 h, the LD samples were vacuum-packaged by using a Kramer-Grebe vacuum-packaging machine and stored at −18°C until further analysis.

Fatty acid analyses

The fatty acid analyses were conducted through service procurement at the Department of Genetics and the Technology, Research and Development Application Center (MARGEM) at the Veterinary Faculty of Mustafa Kemal University.

Fatty acid sample preparation

For the fatty acid analyses, fat was extracted from the muscle samples by using the method described by Bligh and Dyer (1959). Approximately 50 mg of extracted fat was saponified with 2 mL of 0.5 N sodium hydroxide (NaOH) at 90°C for 2 min. After the saponification process, the samples were allowed to cool, then 35% boron trifluoride in methanol was added, and the mixture was kept at 90°C for 5 min. Subsequently, 2 mL of n-heptane was added, and the mixture was maintained at 90°C for 1 min. Following this, 3 mL of saturated sodium chloride (NaCl) solution was added, the mixture was manually shaken, and after phase separation, the upper organic phase was collected into gas chromatography–mass spectrometry (GC-MS) vials. The fatty acid methyl esters in the heptane phase were stored at −20°C until analysis.

GC-MS analysis

After being concentrated under nitrogen gas, the fatty acid methyl esters were analysed using a GC-MS (HP 68905972). An Agilent HP 88 capillary column (100 m length, 0.25 mm inner diameter, 0.20 μm film) was utilised for the GC-MS analysis. The injector temperature was set at 250°C, and the detector temperature at 270°C. Before injection, the injector was washed three times with n-heptane. The injection was performed automatically with a volume of 1 μL and a split ratio of 1:50. The initial column temperature was 150°C, and the final temperature was 240°C, with an increase of 3°C per minute. Helium served as the carrier gas.

Genetic analyses

RNA isolation and c-DNA synthesis

The LD muscle samples from Kıvırcık and Hungarian Merino lambs were rapidly frozen in liquid nitrogen and stored at −80°C until analysis. Total RNA was manually extracted from the LD muscle samples by using Trizol reagent (TriPure Trizol, Sigma, Cat. No.: 11 667 157 001) (Méndez et al. 2011). To prevent DNA contamination, the isolated RNA samples were treated with the Invitrogen DNA-free DNA removal kit (Invitrogen, Cat No: AM1906) and then subjected to agarose gel electrophoresis (70 V, 30 mA). The quality and quantity of the RNA samples were assessed using a Nanodrop device (Synergy H1Hybrid MultiMode Microplate Reader, BioTek, USA). Only RNA samples with an optical density (OD) range of 1.9–2.1 were selected for complementary DNA (c-DNA) synthesis, which was performed using the Transcriptor First Strand c-DNA Synthesis Kit (Roche, Mannheim, Germany, Cat No: 04379012001) according to the manufacturer’s instructions.

RT-qPCR analysis

Real time–quantitative polymerase chain reaction (RT-qPCR) analyses were conducted using a Light Cycler Nano Real-Time PCR device (Roche) with the Fast Start SYBR Green Master Mix (Roche, No: 4673484001) kit, following the manufacturer’s instructions. Each RT-qPCR analysis was repeated three times, and a melting curve analysis was performed for each repetition (Arslan et al. 2022). The threshold cycle (Ct) data for the genes under investigation (Table 1) were normalised using housekeeping genes. The normalised data were further processed using the 2−ΔΔCt method (Livak and Schmittgen 2001) to optimise them for statistical analysis.

Table 1.Primary sequences used in RT-qPCR analysis.

GeneGene IDPrimer sequenceAmplicon size (bp)Reference
PPAR-α443457F5′-TGCCAAGATCTGAAAAAGCA-3′101 Arslan et al. (2022)
R5′-CCTCTTGGCCAGAGACTTGA-3′
PPAR-γ443513F5′-ACTTTGGGATCAGCTCCGTG-3′137 Deng et al. (2018)
R5′-GTCAGCTCTTGGGAACGGAA-3′
PCK2101120669F5′-GTGCTAGACTGGATCTGCCG-3′119Primer 3 software
R5′-GTGGTGTCTATGGCTCCCAG-3′
SCD443185F5′-CCCAGCTGTCAGAGAAAAGG-3′115 Arslan et al. (2022)
R5′-GATGAAGCACAACAGCAGGA-3′
LEP443534F5′-ATGGACCAGACATTGGCAATCT-3′63 Tsiplakou et al. (2009)
R5′-GGATCACATTTCTGGAAGGCAG-3′
FABP4100137067F5′-CATGAAAGAAGTGGGTGTGG-3′145Primer 3 software
R5′-GCCCAATTTGAAGGACATCT-3′
FASN100170327F5′-GTGTGGTACAGCCCCTCAAG-3′110 Malau-Aduli et al. (2015)
R5′-ACGCACCTGAATGACCACTT-3′
GAPDH443005F5′-GATCAAGAAGGTGGTGAAG-3′118 Alan et al. (2022)
R5′-ATCGAAGGTAGAAGAGTGAG-3′
ACTN443052F5-GGACCTGACGGACTACCTCATG-3′136 Dervishi et al. (2011)
R5-GGCCATCTCCTGCTCGAAGT-3′

F, forward primer; R, reverse primer.

Statistical analysis

The Shapiro–Wilk test was applied to assess the normality of gene expression data, because it is suitable for small to moderate sample sizes. After confirming that the data followed a normal distribution, the independent samples Student’s t-test was used to compare gene expression levels between Kivircik and Hungarian Merino lambs. The assumption of homogeneity of variances was tested using Levene’s test, and found to be satisfied. Additionally, the relationships between the expression levels of the studied genes were analysed using Pearson correlation coefficients, calculated separately for the Kivircik and Hungarian Merino breeds. The stepwise regression method was chosen to identify the most predictive subset of explanatory variables for each individual fatty acid, because it is useful for exploratory modelling where the most relevant predictors are not known a priori. The independent variables in the initial regression models included the expression levels of PPAR-α, PPAR-γ, PCK2, SCD, LEP, FABP4, and FASN genes. The inclusion and exclusion of predictors in the model were guided by the F value, with criteria set as F to enter = 3.84 and F to remove = 2.71. To assess multicollinearity, variance inflation factors (VIF) were calculated, where a VIF of <10 indicated an absence of multicollinearity. All statistical analyses were conducted using SPSS (ver. 25.0; IBM SPSS Statistics for Windows, IBM Corporation, Armonk, NY, USA).

Results

The expression levels of the genes examined in the study of in Kivircik and Hungarian Merino lambs are presented in Table 2.

Table 2.Expression levels of examined genes in Kivircik and Hungarian Merino lambs (mean ± s.e.).

GeneKivircik (n = 10)Hungarian Merino (n = 10)P-value
PPAR-α0.00 ± 0.120.05 ± 0.290.874
PPAR-γ0.00 ± 0.132.07 ± 0.41<0.001***
PCK20.00 ± 0.210.36 ± 0.240.273
SCD0.00 ± 0.16−0.81 ± 0.10<0.001***
LEP0.00 ± 0.151.93 ± 0.25<0.001***
FABP40.00 ± 0.68−0.02 ± 0.320.981
FASN0.00 ± 0.16−0.84 ± 0.21<0.01**

**P< 0.01; ***P< 0.001.

SCD and FASN gene expression levels were found to be statistically higher in Kivircik lambs than in Hungarian Merino lambs. However, it is seen that PPAR-γ and LEP gene expression levels were higher in Hungarian Merino lambs. In terms of expression levels of PPAR-α, PCK2 and FABP4 genes, the differences between lambs from both breeds were not significant.

The Pearson correlation coefficients between the expression levels of the examined genes are presented in Table 3.

Table 3.Pearson correlation coefficients between expression levels of examined genes in Kivircik and Hungarian Merino lambs.

GenePPAR-αPPAR-γPCK2SCDLEPFABP4FASN
PPAR-α0.178−0.329−0.3870.673*0.261−0.405
PPAR-γ0.693*−0.1580.186−0.1730.640*−0.275
PCK20.040−0.304−0.0080.290−0.0800.611
SCD0.2180.0060.2190.2900.578−0.390
LEP0.4200.0740.3690.279−0.1870.150
FABP40.594−0.4910.255−0.1680.341−0.456
FASN−0.116−0.041−0.175−0.6400.023−0.043

Correlation coefficients above the diagonal belong to the Kivircik breed, and below the correlation coefficients belong to the Hungarian Merino breed.

*P < 0.05.

In the Kivircik breed, the expression levels of the PPAR-α and LEP genes were found to negatively correlate with each other (r = −0.673, P < 0.05), whereas the expression levels of the PPAR-γ and FABP4 genes were determined to positively correlate with each other (r = 0.640, P < 0.05). In the Hungarian Merino breed, the expression levels of the PPAR-γ and PPAR-α genes were found to negatively correlate with each other (r = −0.693, P < 0.05).

The expression levels of genes included in the model that best explains the observed variance according to the step-wise regression analyses for various fatty acid levels are summarised in Table 4 for Kivircik lambs.

Table 4.Determinants of individual fatty acids according to step-wise regression analysis in Kivircik lambs.

Fatty acidPPAR-αPPAR-γPCK2SCDLEPFABP4FASNAdj. R2P-value
SFAs
 C8:00.3620.039*
 C10:0
 C12:00.3600.039*
 C14:0
 C15:0
 C16:0
 C17:00.4680.046*
 C18:00.6050.016*
 C20:00.5110.034*
 C21:00.7140.014*
 C22:0
 C23:0
 C24:00.7700.007**
MUFAs
 C14:10.2720.070
 C15:10.5970.017*
 C16:1
 C17:1
 C18:10.2490.081
 C20:10.6930.007**
 C22:10.8710.001***
 C24:10.6720.002**
n-3 PUFAs
 C18:3 n-30.2770.068
 C20:3 n-30.8090.001***
 C20:5 n-30.6200.004**
 C22:6 n-3
n-6 PUFAs
 C18:2 n-6 trans0.5020.013*
 C18:2 n-6 cis
 C18:3 n-60.4840.015*
 C20:2 n-60.8440.002**
 C20:3 n-60.7260.004**
 C20:4 n-6
 C22:2 n-60.4620.018*

Adj. R2, adjusted coefficient of determination. *P < 0.05; **P < 0.01; ***P < 0.001.

When the regression models that best explain individual saturated fatty acids in Kivircik lambs are examined, it is seen that LEP gene expression level was a predictor in the models for octanoic acid (C8:0), lauric acid (C12:0), stearic acid (C18:0), arachidic acid (C20:0), and tetracosanoic acid (C24:0) (Table 4). PPAR-γ gene expression level was also a predictor in the models determined for heptadekanoic acid (C17:0), C18:0, C20:0 and C24:0. In contrast, the regression models that explain the variances for decanoic acid (C10:0), myristic acid (C14:0), pentadekanoic acid (C15:0), palmitic (C16:0), behenic acid (C22:0) and trikosanoic acid (C23:0) in Kivircik lambs could not be developed by the gene expression levels investigated in the study. The best model for predicting C18:0 in Kivircik lambs included expression levels of PPAR-γ and LEP genes (P < 0.05). This model explained 60.5% of the total variance. Also, a major proportion (77%) of the variance observed in C24:0 was explained by expression levels of PPAR-γ, LEP, and FASN genes in Kivircik lambs.

When MUFA results of Kivircik lambs were investigated, it appears that LEP gene expression level was an important predictor for all individual MUFAs, except palmitoleic acid (C16:1), heptadecenoic acid (C17:1) and oleic acid (C18:1). It is seen that the majority of variances observed in dokozenoik asit (C22:1) (87.1%) were explained by the expression levels of the genes investigated in the current study (Table 4).

LEP appears to be an important determinant of n-3 PUFAs in Kivircik lambs. This gene explained alone 27.7% and 62% of the total variance in alpha-linolenic acid (ALA; C18:3 n-3) and eicosapentaenoic acid (EPA; C20:5 n-3) respectively (Table 4).

When Kivircik lambs’ n-6 PUFAs results were investigated, the expression level of LEP was among the determinants of eicosadienoic acid (C20:2 n-6), dihomo-γ-linolenic acid (DGLA; C20:3 n-6) and docosadienoic acid (C22:2 n-6) (Table 4). This gene explained alone 46.2% of the total variance in C22:2 n-6. In contrast, the expression level of the PPAR-α gene was the main determinant of C linoleic acid (LA; C18:2 n-6) trans in Kivircik lambs, and that gene alone explained 50.2% of the variance in C18:2 n-6 trans. The expression level of the PPAR-γ gene explained alone 48.4% of the variance in C18:3 n-6. The model, which included expression levels of PPAR-γ, PCK2, and LEP genes, explained 84.4% of the variance in C20:2 n-6. No regression equation could be fitted using the expression levels of examined genes for C18:2 n-6 cis and arachidonic acid (C20:4 n-6) in Kivircik lambs.

The expression levels of genes included in the model that best explains the observed variance according to the step-wise regression analyses for various fatty acid levels are summarised in Table 5 for Hungarian Merino lambs.

Table 5.Determinants of individual fatty acids according to step-wise regression analysis in Hungarian Merino lambs.

Fatty acidPPAR-αPPAR-γPCK2SCDLEPFABP4FASNAdj. R2P-value
SFAs
 C8:00.3800.046*
 C10:00.5050.019*
 C12:00.9750.001***
 C14:00.2950.076
 C15:00.8490.005**
 C16:00.6240.007**
 C17:0
 C18:0
 C20:00.5290.016*
 C21:00.7290.023*
 C22:00.3590.052
 C23:00.4080.038*
 C24:00.7780.005**
MUFAs
 C14:10.5540.013*
 C15:10.4690.025*
 C16:1
 C17:1
 C18:1
 C20:1
 C22:10.5280.016*
 C24:10.2960.075
n-3 PUFAs
 C18:3 n-30.7040.011*
 C20:3 n-30.9190.005**
 C20:5 n-30.8040.001***
 C22:6 n-30.5090.019*
n-6 PUFAs
 C18:2 n-6 trans0.6510.018*
 C18:2 n-6 cis0.2690.087
 C18:3 n-60.6470.005**
 C20:2 n-6
 C20:3 n-60.5380.042*
 C20:4 n-60.5840.010**
 C22:2 n-6

Adj. R2, adjusted coefficient of determination. *P < 0.05; **P < 0.01; ***P < 0.001.

According to the results of step-wise regression analyses for SFAs in Hungarian Merino lambs, PCK2 gene expression level was a predictor in the models for C12:0, C15:0, C16:0 and C21:0 (Table 5). The FASN gene expression level was also determinant of four individual SFAs. It is seen that step-wise regression models developed with the expression levels of the investigated genes in Hungarian Merino lambs explain almost all of the variance observed in terms of C12:0. The model, which included expression levels of PPAR-α, PCK2 and FASN genes, explained 97.5% of the variance in C12:0. In contrast, the best model for predicting C16:0 in Hungarian Merino lambs included expression level of PCK2 gene. This model explained 62.4% of the total variance. Regarding C21:0, the PCK2, LEP, and PCK2 genes appear to explain 72.9% of the total variation. A remarkable result is that the LEP gene expression level alone was the main determinant of C20:0 and C22:0, explaining 52.9% and 35.9% of the total variance for these fatty acids respectively.

Regarding C14:1, the SCD gene appears to explain 55.4% of the total variation. The expression level of the PPAR-γ gene explained alone 52.8% of the variance in C22:1. No regression equation could be fitted using expression levels of examined genes for palmitoleic acid (C16:1), heptadecenoic acid (C17:1), oleic acid (C18:1), and eicosenoic acid (C20:1) in Hungarian Merino lambs.

The expression levels of the genes considered in the study seem to explain most of the variation observed in individual n-3 PUFAs in Hungarian Merino lambs. The model that included expression levels of SCD and LEP genes explained 70.4% of the variance in C18:3 n-3. PPAR-α gene alone explained 80.4% of the variance in C20:5 n-3. The best model for predicting C20:3 n-3 in Hungarian Merino lambs included the expression level of SCD, LEP, FABP4, and FASN genes. This model explained 91.9% of the total variance.

When n-6 PUFA results of Hungarian Merino lambs were investigated, PCK2 and LEP genes explained 65.1% of the total variation in C18:2 n-6 trans. The expression level of the LEP gene was the main determinant of C18:3 n-6 in Hungarian Merino lambs and that gene alone explained 64.7% of the variance in C18:3 n-6. In contrast, FASN gene expression level alone was the main determinant of C20:4 n-6, explaining 58.4% of the total variance for that fatty acid.

Discussion

Breed-specific gene expression

Whereas the genes and pathways regulating a specific trait may be the same within a species, the expression levels of these genes can vary among different breeds (Ji et al. 2014a, 2014b). Such differences in gene expression levels lead to phenotypic differences between breeds for the trait in question (Lehnert et al. 2007). It has been reported that, in cattle, the expression levels of the PPAR-γ, SCD, and LEP genes vary among individual animals on the basis of the level of IMF deposition (Lim et al. 2015). Similar to this case observed in cattle, the present study found that the expression levels of four (PPAR-γ, SCD, LEP, and FASN) of the seven investigated genes differed between the Kivircik and Hungarian Merino breeds. Of these genes, PPAR-γ and LEP were determined to have been expressed at higher levels in the Hungarian Merino than in the Kivircik breed. In contrast, the expression levels of the SCD and FASN genes were determined to be higher in the Kivircik than in the Hungarian Merino. The leptin hormone participates in mammalian fat deposition and bodyweight gain together with PPAR-γ (Geronikolou et al. 2021), and during adipogenic differentiation, the expression level of the PPAR-γ gene increases (Yin et al. 2006; Yi et al. 2019). Thus, in this study, the concurrent increase observed in the expression levels of these two genes (PPAR-γ and LEP) is consistent with the literature. Nowacka-Woszuk (2020) reported that LEP and SCD transcription levels varied among different breeds. Furthermore, Biddinger et al. (2006) found that in mice, the hormone LEP inhibited the transcript SCD, and the protein SCD inhibited SCD activity. The decrease observed in the present study in the expression level of the SCD gene, despite the increase in the expression level of LEP, aligns with the findings previously reported by Biddinger et al. (2006) and Nowacka-Woszuk (2020).

SFAs

Research has shown that the genetic structure of an organism plays an important role in determining the concentrations of SFAs, MUFAs, and PUFAs in this organism (Coltell et al. 2020; Guerrero-Esperanza et al. 2023). Arachidic acid (C20:0), a saturated fatty acid, is crucial for human health because of its effects on cell membrane viscosity and flexibility, inflammation, immune system functions, and cerebral health (Tallima and El Ridi 2018). The LEP gene is involved in the synthesis of this fatty acid (Milanski et al. 2009). In their study on Friesian sheep, Tsiplakou et al. (2012) determined that the C20:0 concentrations were correlated with the LEP concentration. Similarly, in the present study, the expression level of the LEP gene was correlated with the C20:0 concentration in both ovine breeds investigated. Moreover, the present study demonstrated that in Kivircik lambs, the expression levels of LEP and PPAR-γ explained 60.5% and 51.1% of the variations in stearic acid (C18:0) and C20:0 respectively, unlike the other SFAs. Thus, it is suggested that the expression levels of the PPAR-γ and LEP genes could serve as potential biomarkers for the prediction of the variation levels of C18:0 and C20:0.

Lignoceric acid (C24:0), the biological mechanism of which has not been fully elucidated, unlike C20:0, is known to exert positive effects on anti-inflammatory and anti-apoptotic metabolic pathways, contrary to other SFAs (Chung et al. 2015). In the present study, the expression levels of the PPAR-γ, LEP, and FASN genes were found to correlate with the concentration of C24:0 in the Kivircik breed, and a similar correlation was observed between the expression levels of the PPAR-γ and FABP4 genes in the Hungarian Merino. Therefore, although a correlation was detected between PPAR-γ gene expression and C24:0 concentrations in both ovine breeds, it was concluded that C24:0 concentrations are regulated by different mechanisms in different breeds.

MUFAs

Given the nutritional relevance of MUFAs in human health, examining gene associations with MUFA concentrations is critical. Compared with SFAs, MUFAs are recognised for their positive effects on both obesity and diabetes mellitus, and thus, the consumption of unsaturated fatty acids instead of saturated fatty acids is recommended to maintain human health (Gillingham et al. 2011). Yang et al. (2013) observed a decrease in plasma LEP concentrations alongside increased expression of the PPAR-γ gene in mice fed a diet containing long-chain MUFAs. In the present study, in the Kivircik lambs, the genes associated with fatty acid variations were PPAR-γ for C20:1, PPAR-α for C22:1, and LEP for C14:1, C15:1, C20:1, C22:1 and C24:1 respectively. In contrast, in the Hungarian Merino lambs, the expressions of the genes SCD, LEP and PPAR-γ were found to be determining for the fatty acids C14:1, C15:1 and C22:1 respectively. The statistically significant results obtained in this study, which align with the findings of Yang et al. (2013), suggest that the PPAR-γ and LEP genes may be involved in the metabolism of MUFAs in the two ovine breeds investigated.

n-3 PUFAs

n-3 PUFAs (omega-3 fatty acids) positively modulate immune functions in humans. The nutritional properties of red meat largely depend on its fat content and fatty acid composition (Díaz et al. 2011). PUFA-rich diets have been found to inhibit LEP secretion in humans (Reseland et al. 2001), fish (Coccia et al. 2014), and rats (Cammisotto et al. 2003). Eicosapentaenoic acid (C20:5 n-3; EPA), a member of the omega-3 fatty acid family, is known to exert biological effects that differ from those of other fatty acids. C20:5 n-3 is associated with beneficial effects on human health because of its anti-inflammatory properties and ability to inhibit cell apoptosis (Tanaka et al. 2008). In rats, SFAs, MUFAs, and PUFAs are indicated to play a crucial metabolic role as messengers during the hormonal activation of lipolysis and the inhibition of LEP secretion from white adipocytes (Cammisotto et al. 2003). Increased levels of C20:5 n-3 inhibit the LEP mRNA, thereby reducing fat around internal organs, and the blood glucose, and cholesterol concentrations (Hun et al. 1999). Consistent with the findings of Murata et al. (2000), who reported that C20:5 n-3 (eicosapentaenoic acid) induces LEP mRNA synthesis, this study found a statistically significant correlation between C20:5 n-3 concentrations and LEP gene expression level in Kivircik lambs.

Given the therapeutic potential of the LEP gene for treating insulin-dependent diabetes (Pereira et al. 2021), the observed correlation between C20:5 n-3 and LEP suggests that C20:5 n-3, often used in dietary supplements, may also hold therapeutic potential for insulin-dependent diabetes. However, further research is required to substantiate this possibility. Apart from genetic differences, the most important factors that can explain the methods of regulation specific to breeds and increase the fatty acid levels in sheep meat are epigenetic and environmental factors (Ibeagha-Awemu and Yu 2021). The nutrition regimen applied to animals during the gestation period and adulthood affects the meat fatty acid profile; in sheep fed with concentrated feed, UFAs increase and SFAs may decrease. This type of feeding can affect the meat quality of the sheep and increase the fatty acid ratios beneficial to human health (Zhang et al. 2022). The study also showed a statistically significant correlation between C20:5 n-3 concentrations and PPAR-α gene expression in Hungarian Merino lambs. This result aligns with previous studies that identified a similar relationship between C20:5 n-3 and PPAR-α expression (Tapia et al. 2014), supporting the current findings.

n-6 PUFAs

The primary representatives of n-6 PUFAs (omega-6 fatty acids) are linoleic acid (C18:2 n-6; LA) and arachidonic acid (C20:4 n-6; AA). These fatty acids, known for their pro-inflammatory properties, are commonly incorporated into the human diet. Studies have shown that C18:2 n-6 and C20:4 n-6 influence inflammatory biomarkers, contributing to the body’s inflammatory response (Djuricic and Calder 2021). Joseph et al. (2010) determined that the dietary supplementation of cattle with maize oil altered the expressions of the main lipogenic genes PPAR-γ, FASN, and SCD. In this study, it was determined that the level of expression of the PPAR-α gene was correlated with the variation in C18:2 n-6, and the level of expression of the PPAR-γ gene was correlated with the variation in C18:3 n-6 in the Kivircik breed. In contrast, in Hungarian Merino sheep, the expression levels of the PCK2 and LEP genes correlated with the variation in C18:2 n-6, whereas the expression levels of the LEP and FASN genes correlated with the variations in C18:3 n-6 and C20:4 n-6 respectively. The findings obtained for the FASN gene are consistent with the literature of Joseph et al. (2010). However, the differences observed for the PPAR-α, LEP, and SCD genes align with the information that fatty acid metabolism is regulated by different mechanisms depending on the breed (Gunawan et al. 2019).

Conclusions

In the present study, it was determined that LEP was a major determining gene for MUFAs, n-3 PUFAs, and n-6 PUFAs in the Kivircik lambs (Table 4). In contrast, in the Hungarian Merino lambs, the SCD gene was ascertained to be determining for n-3 PUFAs (Table 5). This was attributed to the fatty acid metabolism being regulated by different mechanisms in different breeds (Gunawan et al. 2019). In farm animals, the primary fatty acids that determine the palatability of meat are PUFAs (Liu et al. 2021). In the present study, whereas the LEP gene explained most of the variations in the PUFAs in the Kivircik lambs, other genes were also effective in fatty acid metabolism in the Hungarian Merino lambs. Therefore, it was concluded that the LEP gene needs to be studied extensively to increase the meat quality of the Kivircik, an ovine breed native to Türkiye. The present study demonstrated the effects of genetic differences between ovine breeds on fatty acid metabolism and gene expression. Particularly, the relationship between the LEP gene and C20:3 n-3, defined in this study, is thought to indicate its potential as a therapeutic agent. However, more comprehensive studies on this topic are needed.

Data availability

The data that support this study will be shared upon reasonable request to the corresponding author.

Conflicts of interest

The authors declare that they have no conflicts of interest.

Declaration of funding

This work has been supported by Erciyes University Scientific Research Projects Unit Grant number TSA-2022-12221.

Acknowledgements

We thank the proofreading and editing office of the Dean for Research at Erciyes University for the copyediting and proofreading service for this paper.

References

Alan A, Alan E, Arslan K, Daldaban F, Aksel EG, Çınar MU, Akyüz B (2022) LPS- and LTA-induced expression of TLR4, MyD88, and TNF-α in lymph nodes of the Akkaraman and Romanov lambs. Microscopy and Microanalysis 28(6), 2078-2092.
| Crossref | Google Scholar |

Anonymous (2011) Regulation on the welfare and protection of animals used for experimental and other scientific purposes. Turkish Official Gazette (No: 28141). [13 December 2011]

Arslan K, Daldaban F, Kecici PD, Aksel EG, Ekiz B, Akyuz B, Yilmaz A, Akcay A, Iscan K (2022) Relationship between transport-induced stress and the expression levels of some genes in the peroxisome proliferator-activated receptor (PPAR) signaling pathway in Kivircik lambs. Small Ruminant Research 212, 106708.
| Crossref | Google Scholar |

Bartoň L, Bureš D, Řehák D, Kott T, Makovický P (2021) Tissue-Specific fatty acid composition, cellularity, and gene expression in diverse cattle breeds. Animal 15(1), 100025.
| Crossref | Google Scholar |

Biddinger SB, Miyazaki M, Boucher J, Ntambi JM, Kahn CR (2006) Leptin suppresses stearoyl-CoA desaturase 1 by mechanisms independent of insulin and sterol regulatory element–binding protein-1c. Diabetes 55(7), 2032-2041.
| Crossref | Google Scholar | PubMed |

Bligh EG, Dyer WJ (1959) A rapid method of total lipid extraction and purification. Canadian Journal of Biochemistry and Physiology 37(8), 911-917.
| Crossref | Google Scholar |

Bureš D, Bartoň L (2018) Performance, carcass traits and meat quality of Aberdeen Angus, Gascon, Holstein and Fleckvieh finishing bulls. Livestock Science 214, 231-237.
| Crossref | Google Scholar |

Cammisotto PG, Gélinas Y, Deshaies Y, Bukowiecki LJ (2003) Regulation of leptin secretion from white adipocytes by free fatty acids. American Journal of Physiology – Endocrinology and Metabolism 285(3), E521-E526.
| Crossref | Google Scholar | PubMed |

Chen N, Zhang Q, Zhi J, Guo H, Gao H, Li F, Huang J, Lei C, Chen H, Ma Y (2018) Chinese yellow cattle PPARA gene: analyses of expression, polymorphism and trait association. Czech Journal of Animal Science 63, 473-482.
| Crossref | Google Scholar |

Cheng W, Cheng J-H, Sun D-W, Pu H (2015) Marbling analysis for evaluating meat quality: methods and techniques. Comprehensive Reviews in Food Science and Food Safety 14(5), 523-535.
| Crossref | Google Scholar |

Chung H, Lee YS, Mayoral R, Oh DY, Siu JT, Webster NJ, Sears DD, Olefsky JM, Ellies LG (2015) Omega-3 fatty acids reduce obesity-induced tumor progression independent of GPR120 in a mouse model of postmenopausal breast cancer. Oncogene 34, 3504-3513.
| Crossref | Google Scholar | PubMed |

Coccia E, Varricchio E, Vito P, Turchini GM, Francis DS, Paolucci M (2014) Fatty acid-specific alterations in leptin, PPARα, and CPT-1 gene expression in the rainbow trout. Lipids 49(10), 1033-1046.
| Crossref | Google Scholar | PubMed |

Coltell O, Sorlí JV, Asensio EM, Barragán R, González JI, Giménez-Alba IM, Zanón-Moreno V, Estruch R, Ramírez-Sabio JB, Pascual EC, Ortega-Azorín C, Ordovas JM, Corella D (2020) Genome-wide association study for serum omega-3 and omega-6 polyunsaturated fatty acids: exploratory analysis of the sex-specific effects and dietary modulation in mediterranean subjects with metabolic syndrome. Nutrients 12(2), 310.
| Crossref | Google Scholar |

Da Costa ASH, Pires VMR, Fontes CMGA, Mestre Prates JA (2013) Expression of genes controlling fat deposition in two genetically diverse beef cattle breeds fed high or low silage diets. BMC Veterinary Research 9, 118.
| Crossref | Google Scholar |

Deng K, Ma T, Wang Z, TanTai W, Nie H, Guo Y, Wang F, Fan Y (2018) Effects of Perilla frutescens seed supplemented to diet on fatty acid composition and lipogenic gene expression in muscle and liver of Hu lambs. Livestock Science 211, 21-29.
| Crossref | Google Scholar |

Dervishi E, Serrano C, Joy M, Serrano M, Rodellar C, Calvo JH (2011) The effect of feeding system in the expression of genes related with fat metabolism in semitendinous muscle in sheep. Meat Science 89(1), 91-97.
| Crossref | Google Scholar | PubMed |

Díaz MT, Cañeque V, Sánchez CI, Lauzurica S, Pérez C, Fernández C, Álvarez I, De la Fuente J (2011) Nutritional and sensory aspects of light lamb meat enriched in n-3 fatty acids during refrigerated storage. Food Chemistry 124(1), 147-155.
| Crossref | Google Scholar |

Djuricic I, Calder PC (2021) Beneficial outcomes of omega-6 and omega-3 polyunsaturated fatty acids on human health: an update for 2021. Nutrients 13(7), 2421.
| Crossref | Google Scholar |

European Union (2010) European Union Directive 2010/63/EU of the European parliament and of the council of 22 September 2010 on the protection of animals used for scientific purposes. OJEU 276, 33-79.
| Google Scholar |

Geronikolou SA, Pavlopoulou A, Cokkinos DV, Bacopoulou F, Chrousos GP (2021) Polycystic ovary syndrome revisited: an interactions network approach. European Journal of Clinical Investigation 51(9), e13578.
| Crossref | Google Scholar |

Gillingham LG, Harris-Janz S, Jones PJH (2011) Dietary monounsaturated fatty acids are protective against metabolic syndrome and cardiovascular disease risk factors. Lipids 46(3), 209-228.
| Crossref | Google Scholar | PubMed |

Guerrero-Esperanza M, Wrobel K, Wrobel K, Ordaz-Ortiz JJ (2023) Determination of fatty acids in vegetable oils by GC-MS, using multiple-ion quantification (MIQ). Journal of Food Composition and Analysis 115, 104963.
| Crossref | Google Scholar |

Gunawan A, Pramukti FW, Listyarini K, Abuzahra MA, Jakaria J, Sumantri C, Inounu I, Uddin MJ (2019) Novel variant in the leptin receptor (LEPR) gene and its association with fat quality, odour and flavour in sheep. Journal of the Indonesian Tropical Animal Agriculture 44(1), 1-9.
| Crossref | Google Scholar |

Guo P−P, Yao X−R, Xu Y−N, Jin X, Li Q, Yan C−G, Kim N−H, Li X−Z (2024) Insulin interacts with PPARγ agonists to promote bovine adipocyte differentiation. Domestic Animal Endocrinology 88, 106848.
| Crossref | Google Scholar |

Hanson RW, Reshef L (2003) Glyceroneogenesis revisited. Biochimie 85(12), 1199-1205.
| Crossref | Google Scholar | PubMed |

Hun CS, Hasegawa K, Kawabata T, Kato M, Shimokawa T, Kagawa Y (1999) Increased uncoupling protein2 mRNA in white adipose tissue, and decrease in leptin, visceral fat, blood glucose, and cholesterol in KK-Ay mice fed with eicosapentaenoic and docosahexaenoic acids in addition to linolenic acid. Biochemical and Biophysical Research Communications 259(1), 85-90.
| Crossref | Google Scholar | PubMed |

Ibeagha-Awemu EM, Yu Y (2021) Consequence of epigenetic processes on animal health and productivity: is additional level of regulation of relevance? Animal Frontiers 11(6), 7-18.
| Crossref | Google Scholar | PubMed |

Ji P, Drackley JK, Khan MJ, Loor JJ (2014a) Inflammation- and lipid metabolism-related gene network expression in visceral and subcutaneous adipose depots of Holstein cows. Journal of Dairy Science 97(6), 3441-3448.
| Crossref | Google Scholar |

Ji S, Yang R, Lu C, Qiu Z, Yan C, Zhao Z (2014b) Differential expression of PPARγ, FASN, and ACADM genes in various adipose tissues and longissimus dorsi muscle from Yanbian yellow cattle and Yan yellow cattle. Asian–Australasian Journal of Animal Sciences 27(1), 10-18.
| Crossref | Google Scholar |

Jin M, Fei X, Li T, Lu Z, Chu M, Di R, He X, Wang X, Wei C (2022) Transcriptome study digs out BMP2 involved in adipogenesis in sheep tails. BMC Genomics 23, 457.
| Crossref | Google Scholar |

Joseph SJ, Pratt SL, Pavan E, Rekaya R, Duckett SK (2010) Omega-6 fat supplementation alters lipogenic gene expression in bovine subcutaneous adipose tissue. Gene Regulation and Systems Biology 4, GRSB.S5831.
| Crossref | Google Scholar | PubMed |

Junkuszew A, Nazar P, Milerski M, Margetin M, Brodzki P, Bazewicz K (2020) Chemical composition and fatty acid content in lamb and adult sheep meat. Archives Animal Breeding 63(2), 261-268.
| Crossref | Google Scholar | PubMed |

Kader Esen V, Karadağ O, Elmaci C, Esen S (2024) Comparison of nonlinear models for predicting live weight growth curves in lamb production of Kıvırcık and Karacabey Merino. Turkish Journal of Veterinary & Animal Sciences 48(3), 126–-137.
| Crossref | Google Scholar |

Kang L, Li X, Zhao X, Liu T, Jin Y, Duan Y (2025) Effects of L-arginine supplementation on fat deposition and meat quality in growing lambs: Interactions with gut microbiota and metabolic signalling pathways. Food Chemistry 479, 143677.
| Crossref | Google Scholar |

Ladeira MM, Schoonmaker JP, Swanson KC, Duckett SK, Gionbelli MP, Rodrigues LM, Teixeira PD (2018) Review: nutrigenomics of marbling and fatty acid profile in ruminant meat. Animal 12(2), S282-S294.
| Crossref | Google Scholar | PubMed |

Lehnert SA, Reverter A, Byrne KA, Wang Y, Nattrass GS, Hudson NJ, Greenwood PL (2007) Gene expression studies of developing bovine longissimus muscle from two different beef cattle breeds. BMC Developmental Biology 7, 95.
| Crossref | Google Scholar |

Lim D, Chai H-H, Lee S-H, Cho Y-M, Choi J-W, Kim N-K (2015) Gene expression patterns associated with peroxisome proliferator-activated receptor (PPAR) signaling in the Longissimus dorsi of Hanwoo (Korean cattle). Asian–Australasian Journal of Animal Sciences 28(8), 1075-1083.
| Crossref | Google Scholar | PubMed |

Liu J, Li X, Hou J, Sun J, Guo N, Wang Z (2021) Dietary intake of n-3 and n-6 polyunsaturated fatty acids and risk of cancer: meta-analysis of data from 32 studies. Nutrition and Cancer 73(6), 901-913.
| Crossref | Google Scholar | PubMed |

Livak KJ, Schmittgen TD (2001) Analysis of relative gene expression data using real-time quantitative PCR and the 2−ΔΔCT method. Methods 25(4), 402-408.
| Crossref | Google Scholar | PubMed |

Loukovitis D, Szabó M, Chatziplis D, Monori I, Kusza S (2023) Genetic diversity and substructuring of the Hungarian merino sheep breed using microsatellite markers. Animal Biotechnology 34(4), 1701-1709.
| Crossref | Google Scholar | PubMed |

Luo M, Wang L, Xiao C, Zhou M, Li M, Li H (2023) miR136 regulates proliferation and differentiation of small tail han sheep preadipocytes. Adipocyte 12(1), 2173966.
| Crossref | Google Scholar |

Malau-Aduli AEO, Otto JR, Suybeng B, Kashani A, Lane PA, Malau-Aduli BS, Nichols PD (2015) Gene expression profiles of aralkylamine N-acetyltransferase, B-cell translocation gene-2 and fatty acid synthase in pasture-based primiparous Holstein-Friesian dairy cows supplemented with crude degummed canola oil. Advancements in Genetic Engineering 4(2), 1-10.
| Crossref | Google Scholar |

Méndez V, Avelar E, Morales A, Cervantes M, Araiza A, González D (2011) A rapid protocol for purification of total RNA for tissues collected from pigs at a slaughterhouse. Genetics and Molecular Research 10(4), 3251-3255.
| Crossref | Google Scholar | PubMed |

Milanski M, Degasperi G, Coope A, Morari J, Denis R, Cintra DE, Tsukumo DML, Anhe G, Amaral ME, Takahashi HK, Curi R, Oliveira HC, Carvalheira JBC, Bordin S, Saad MJ, Velloso LA (2009) Saturated fatty acids produce an inflammatory response predominantly through the activation of TLR4 signaling in hypothalamus: implications for the pathogenesis of obesity. The Journal of Neuroscience 29(2), 359-370.
| Crossref | Google Scholar | PubMed |

Murata M, Kaji H, Takahashi Y, Iida K, Mizuno I, Okimura Y, Abe H, Chihara K (2000) Stimulation by eicosapentaenoic acids of leptin mRNA expression and its secretion in mouse 3T3-L1 adipocytes in vitro. Biochemical and Biophysical Research Communications 270(2), 343-348.
| Crossref | Google Scholar | PubMed |

Nowacka-Woszuk J (2020) Nutrigenomics in livestock: recent advances. Journal of Applied Genetics 61, 93-103.
| Crossref | Google Scholar | PubMed |

Panayotov D (2021) Study on chemical composition, fatty acid composition and technological quality of meat in Boer goat kids. Bulgarian Journal of Agricultural Science 27, 1248-1257.
| Google Scholar |

Pereira S, Cline DL, Glavas MM, Covey SD, Kieffer TJ (2021) Tissue-specific effects of leptin on glucose and lipid metabolism. Endocrine Reviews 42, 1-28.
| Crossref | Google Scholar | PubMed |

Pethick DW, Hocquette JF, Scollan ND, Dunshea FR (2021) Improving the nutritional, sensory, and market value of meat products from sheep and cattle. Animal 15, 100356.
| Crossref | Google Scholar |

Reseland JE, Haugen F, Hollung K, Solvoll K, Halvorsen B, Brude IR, Nenseter MS, Christiansen EN, Drevon CA (2001) Reduction of leptin gene expression by dietary polyunsaturated fatty acids. Journal of Lipid Research 42(5), 743-750.
| Crossref | Google Scholar | PubMed |

Roy R, Taourit S, Zaragoza P, Eggen A, Rodellar C (2005) Genomic structure and alternative transcript of bovine fatty acid synthase gene (FASN): comparative analysis of the FASNgene between monogastric and ruminant species. Cytogenetic and Genome Research 111(1), 65-73.
| Crossref | Google Scholar | PubMed |

Şengül Ö, Çelik Ş (2025) Final weight prediction from body measurements in Kıvırcık lambs using data mining algorithms. Archives Animal Breeding 68(2), 325-337.
| Crossref | Google Scholar |

Shin SC, Chung ER (2007) Association of SNP marker in the leptin gene with carcass and meat quality traits in Korean cattle. Asian–Australasian Journal of Animal Sciences 20(1), 1-6.
| Crossref | Google Scholar |

Tallima H, El Ridi R (2018) Arachidonic acid: physiological roles and potential health benefits – a review. Journal of Advanced Research 11, 33-41.
| Crossref | Google Scholar | PubMed |

Tan Z, Jiang H (2024) Molecular and cellular mechanisms of intramuscular fat development and growth in cattle. International Journal of Molecular Sciences 25(5), 2520.
| Crossref | Google Scholar |

Tanaka N, Sano K, Horiuchi A, Tanaka E, Kiyosawa K, Aoyama T (2008) Highly purified eicosapentaenoic acid treatment improves nonalcoholic steatohepatitis. Journal of Clinical Gastroenterology 42(4), 413-418.
| Crossref | Google Scholar | PubMed |

Taniguchi M, Mannen H, Oyama K, Shimakura Y, Oka A, Watanabe H, Kojima T, Komatsu M, Harper GS, Tsuji S (2004) Differences in stearoyl–CoA desaturase mRNA levels between Japanese Black and Holstein cattle. Livestock Production Science 87(2–3), 215-220.
| Crossref | Google Scholar |

Tapia G, Valenzuela R, Espinosa A, Romanque P, Dossi C, Gonzalez-Mañán D, Videla LA, D’Espessailles A (2014) N-3 long-chain PUFA supplementation prevents high fat diet induced mouse liver steatosis and inflammation in relation to PPAR-α upregulation and NF-κB DNA binding abrogation. Molecular Nutrition & Food Research 58(6), 1333-1341.
| Crossref | Google Scholar | PubMed |

Tsiplakou E, Flemetakis E, Kalloniati C, Papadomichelakis G, Katinakis P, Zervas G (2009) Sheep and goats differences in CLA and fatty acids milk fat content in relation with mRNA stearoyl–CoA desaturase and lipogenic genes expression in their mammary gland. Journal of Dairy Research 76(4), 392-401.
| Crossref | Google Scholar | PubMed |

Tsiplakou E, Chadio S, Zervas G (2012) The effect of long term under- and over-feeding of sheep on milk and plasma fatty acid profiles and on insulin and leptin concentrations. Journal of Dairy Research 79(2), 192-200.
| Crossref | Google Scholar | PubMed |

Xu Y-X, Wang B, Jing J-N, Ma R, Luo Y-H, Li X, Yan Z, Liu Y-J, Gao L, Ren Y-L, Li M-H, Lv F-H (2023) Whole-body adipose tissue multi-omic analyses in sheep reveal molecular mechanisms underlying local adaptation to extreme environments. Communications Biology 6(1), 159.
| Crossref | Google Scholar |

Xu X, Zhan C, Qiao J, Yang Y, Li C, Li P, Ma S (2025) Transcriptomic analysis of muscle satellite cell regulation on intramuscular preadipocyte differentiation in tan sheep. International Journal of Molecular Sciences 26(7), 3414.
| Crossref | Google Scholar | PubMed |

Yang Z-H, Miyahara H, Iwasaki Y, Takeo J, Katayama M (2013) Dietary supplementation with long-chain monounsaturated fatty acids attenuates obesity-related metabolic dysfunction and increases expression of PPAR gamma in adipose tissue in type 2 diabetic KK-Ay mice. Nutrition & Metabolism 10, 16.
| Crossref | Google Scholar |

Yang XR, Yu B, Mao XB, Zheng P, He J, Yu J, He Y, Reecy JM, Chen DW (2015) Lean and obese pig breeds exhibit differences in prenatal gene expression profiles of muscle development. Animal 9(1), 28-34.
| Crossref | Google Scholar | PubMed |

Yi X, Wu P, Liu J, Gong Y, Xu X, Li W (2019) Identification of the potential key genes for adipogenesis from human mesenchymal stem cells by RNA-Seq. Journal of Cellular Physiology 234(11), 20217-20227.
| Crossref | Google Scholar | PubMed |

Yin Y, Yuan H, Wang C, Pattabiraman N, Rao M, Pestell RG, Glazer RI (2006) 3-Phosphoinositide-dependent protein kinase-1 activates the peroxisome proliferator-activated receptor-γ and promotes adipocyte differentiation. Molecular Endocrinology 20(2), 268-278.
| Crossref | Google Scholar |

Zhang Z, Wang X, Jin Y, Zhao K, Duan Z (2022) Comparison and analysis on sheep meat quality and flavor under pasture-based fattening contrast to intensive pasture-based feeding system. Animal Bioscience 35(7), 1069-1079.
| Crossref | Google Scholar | PubMed |

Zhou L, Raza SHA, Gao Z, Hou S, Alwutayd KM, Aljohani ASM, Abdulmonem WA, Alghsham RS, Aloufi BH, Wang Z, Gui L (2024) Fat deposition, fatty acid profiles, antioxidant capacity and differentially expressed genes in subcutaneous fat of Tibetan sheep fed wheat-based diets with and without xylanase supplementation. Journal of Animal Physiology and Animal Nutrition 108, 252-263.
| Crossref | Google Scholar |