Analysis of quality and antibiotic residues in raw milk marketed in the Chaco Province of Napo, EcuadorAbstract
Milk quality monitoring is essential to guarantee food safety and identify factors affecting the physicochemical characteristics of dairy products. This study aimed to evaluate the physicochemical quality and detect antibiotic residues in raw milk marketed in El Chaco Canton, Napo Province, Ecuador. A total of 500 raw milk samples were collected from 32 farms distributed across seven productive sectors during four sampling periods. Milk composition parameters, including fat, protein, lactose, and non-fat solids, were determined by infrared spectrophotometry. Somatic cell count (SCC), Dornic acidity, alcohol stability, and qualitative detection of β-lactam, sulfonamide, and tetracycline residues were also evaluated. The results showed that fat (4.38 ± 1.63%), protein (3.05 ± 0.51%), lactose (4.57 ± 0.66%), and SCC (5.65 log10; 448,252 cells/mL) values were within the ranges established by Ecuadorian regulations. Significant differences among productive sectors were observed for non-fat solids, density, Dornic degrees, and SCC (P < 0.05), suggesting variability associated with production conditions, feeding management, and animal health status. Lactose concentration and SCC showed significant differences among sampling periods, indicating temporal variation in milk composition and udder health indicators. Antibiotic residues were detected in 1% of the analyzed samples; however, these results should be interpreted as screening findings that require confirmation through quantitative analytical methods. Overall, raw milk marketed in El Chaco showed acceptable physicochemical characteristics and complied with the evaluated quality parameters. Nevertheless, continuous monitoring, improved hygienic practices, and responsible antimicrobial management are necessary to strengthen milk safety and quality in rural dairy production systems.
Keywords:
milk quality; antibiotics; adulterants; food safety; milking
Resumo
O monitoramento da qualidade do leite é essencial para garantir a segurança alimentar e identificar fatores que afetam as características físico-químicas dos produtos lácteos. Este estudo teve como objetivo avaliar a qualidade físico-química e detectar resíduos de antibióticos em leite cru comercializado no Cantão de El Chaco, Província de Napo, Equador. Um total de 500 amostras de leite cru foram coletadas de 32 fazendas distribuídas em sete setores produtivos durante quatro períodos de amostragem. Os parâmetros de composição do leite, incluindo teor de gordura, proteína, lactose e sólidos não gordurosos, foram determinados por espectrofotometria infravermelha. A contagem de células somáticas (CCS), a acidez de Dornic, a estabilidade ao álcool e a detecção qualitativa de resíduos de β-lactâmicos, sulfonamidas e tetraciclinas também foram avaliadas. Os resultados mostraram que os teores de gordura (4,38 ± 1,63%), proteína (3,05 ± 0,51%), lactose (4,57 ± 0,66%) e CCS (5,65 log10; 448.252 células/mL) estavam dentro dos limites estabelecidos pela legislação equatoriana. Diferenças significativas entre os setores produtivos foram observadas para sólidos não gordurosos, densidade, grau Dornic e CCS (P < 0,05), sugerindo variabilidade associada às condições de produção, manejo alimentar e estado sanitário dos animais. A concentração de lactose e a CCS apresentaram diferenças significativas entre os períodos de amostragem, indicando variação temporal na composição do leite e nos indicadores de saúde da glândula mamária. Resíduos de antibióticos foram detectados em 1% das amostras analisadas; entretanto, esses resultados devem ser interpretados como achados de triagem, que requerem confirmação por meio de métodos analíticos quantitativos. De modo geral, o leite cru comercializado em El Chaco apresentou características físico-químicas aceitáveis e atendeu aos parâmetros de qualidade avaliados. No entanto, a monitorização contínua, a melhoria das práticas de higiene e a gestão antimicrobiana responsável são necessárias para reforçar a segurança e a qualidade do leite nos sistemas rurais de produção leiteira.
Palavras-chave:
qualidade do leite; antibióticos; adulterantes; segurança alimentar; ordenha
1. Introduction
According to the FAO (2021), demographic projections indicate that the world population will reach 9.8 billion by 2050 (Elgersma et al., 2006). On the other hand, (Puga-Torres et al., 2024)report that deficiencies in protein, micronutrients, and vitamins lead to malnutrition in approximately 2 billion people. Milk is a nutritious food, free of undesirable odors and with a pleasant taste (Pereira, 2014). Furthermore, from a chemical composition standpoint, it is considered free of contaminants or pathogens (Alves et al., 1996). Consequently, milk is composed of approximately 13% solids, with lactose being the main carbohydrate, representing 4.7%, followed by fat (3.7%) in order of nutritional importance, while proteins range from 3.2 to 3.4% depending on the bovine biotype (Bonfoh et al., 2005).
Ecuador, with an area of 256,370 km2, is geographically divided into four natural regions: Coast, Andes (highlands), Amazon, and Galápagos Islands (Cornejo and Wilkie, 2010). One of its most striking features is its diverse climates, ranging from frigid zones (Papallacta) to tropical zones (Amazon and Coast) (Wasserstrom and Bustamante, 2013). Global data for 2023 report milk production of 965.5 million tons and meat production of 76.6 million tons (Paucar-Quishpe et al., 2024). According to data from INEC-ESPAC (Ecuador, 2025), milk production in Ecuador in 2022 was 5.5 million liters, concentrated in the central highland provinces of Pichincha, Cotopaxi, and Chimborazo. However, in terms of productivity per cow, the Sierra region leads with 7.7 liters/cow/day, followed by the Amazon region with 5.5 liters/cow/day, while the Costa region registers an average of 4.3 liters/cow/day (Ecuador, 2025).
On the other hand, the use of antibiotics in the dairy industry is a common practice to combat various diseases affecting livestock, such as mastitis, pneumonia, and other infections (Alves et al., 1996; Walther et al., 2022). However, indiscriminate use has led to alarming levels of resistance in a wide range of microorganisms (Mobarki et al., 2019; Walther et al., 2022; Wu and Zeng, 2024). This problem has raised concerns in the international community due to its implications for human health and food safety (Founou et al., 2016; Wu and Zeng, 2024). Although the national regulations issued by the Ecuadorian Technical Standard (NTE) INEN establish parameters for evaluating the quality of raw milk and based on this evaluation, determining its suitability for human consumption. Factors related to management, feeding, and health have been observed to potentially influence the quality of raw milk. In this regard, Paredes-Peralta et al. (2024), in a study in the northern Amazon region of Ecuador, identified three types of producers at different levels of technological development, namely subsistence family farms with low technification, semi‑specialized medium‑scale producers, and specialized commercial units with higher adoption of technology. Taking these arguments into consideration, this study aimed to analyze milk quality and the presence of antibiotic residues in raw milk sold in the El Chaco Canton, Ecuador.
2. Materials and Methods
2.1. Location of the study area
This research was conducted in the Chaco Canton, Napo Province, located in the northern part of the Ecuadorian Amazon region. The Chaco Canton has an altitude of 1,650 meters above sea level and is characterized by a rainy climate with an average temperature of 18 °C (Ecuador, 2021). El Chaco Canton has 7,960 inhabitants (Ecuador, 2025) and is territorially distributed among the following parishes: González Díaz de Pineda, Linares, Oyacachi, Santa Rosa de Quijos, and Sardinas. This area boasts high biodiversity, including clean rivers, organic farms, fish farms, dairy cattle ranches, and the cultivation of naranjilla (lulo), tomatoes, and other crops.
2.2. Population and sampling frame
This study was a descriptive, observational, longitudinal study (Altman, 1991; Stroup et al., 2000). In this study, the experimental unit was the individual raw milk sample collected from a lactating cow. The sampling frame consisted of all dairy farms that sell raw milk informally in the seven main productive sectors of El Chaco canton. For this purpose, convenience samples of raw milk, which is commonly sold informally, were collected frm the seven main productive sectors of the Chaco Canton (Ecuador, 2021). Therefore, A total of 32 farms and 200 lactating cows were included. Samples were collected from the same set of farms across four sampling periods, so observations were repeated over time at the farm level but considered independent at the sample level within each period. The 500 observations resulted from 4 sampling rounds (every 15 days), totaling 125 samples per period distributed across the seven sectors in proportion to their contribution to total milk production
2.3. Sampling and laboratory analysis
For sample collection, we first washed each teat with clean water and dried it with paper towels. Using a sterile 50 mL plastic bottle, we discarded the first stream from each quarter and collected the milk in the container, labeling the animal's name, sector, and sampling date with Bronopol (Broad Spectrum Micro-tabs II, D&F Control Systems Inc., San Ramon, California). The samples were kept in a cooler at 4°C with refrigerant gel for transport to the Laboratory of the Higher Polytechnic School of Chimborazo, Orellana Campus. For analysis, the samples were brought to room temperature in the laboratory and then analyzed by infrared spectrophotometry to determine the content of protein, fat, lactose, and non-fat solids. The somatic cell count (SCC) was evaluated using a Draminski instrument calibrated for cow's milk samples (Ali and Dahl, 2022; Siddiquee et al., 2014). Similarly, titratable acidity was determined using the Dornic degree technique, and protein stability was assessed with the 68% alcohol test. Finally, the presence of antibiotics was detected using AMINO 3IN1 and 3IN1 BTS reagent strips (Shenzhen Bioeasy Biotechnology Co., Ltd., Shenzhen, China 518101).
2.4. Statistical analysis
All milk chemical composition data were subjected to normality tests (Kolmogorov; P > 0.05), while the SCC data were previously logarithmically transformed (log10) to assume a normal distribution. Subsequently, descriptive statistics and a repeated measures analysis of variance (general linear model) were performed, considering the sector and sampling period as the main effects. Means are presented as least significant differences (PDIFF) and compared using Tukey's test. In addition, regression and correlation analyses were conducted to identify associations between the different variables. Statistical differences were declared at P < 0.05.
3. Results
Analysis of the results in Table 1 reveals that the mean values obtained for fat, protein, and lactose did not vary when compared between sectors (P > 0.05). However, although non-fat solids content, density, Dornic degrees, and SCC showed statistically significant differences between sectors (P = 0.02 to 0.001; Table 1), it is noteworthy that these values were within the ranges established in Ecuador's NTE INEN 9 standard. Therefore, from a nutritional standpoint, a mean fat content of (4.46 ± 1.63%) indicates that the raw milk analyzed has a favorable lipid profile, although this component could be partly explained by the nutritional status, as well as the breed and age of the animal. Likewise, the protein content (3.06 ± 0.51%) is also above the minimum requirement of 2.9%, which is extremely important for maintaining the milk's nutritional value. For lactose, current Ecuadorian regulations do not establish maximum or minimum levels for raw milk (INEN, 2012). However, for reference, the approximate percentage is 5%, considering that these values could vary depending on the breed of cow, its diet, and its health. Regarding density, an essential indicator of milk quality and purity, it falls within the established ranges according to current national regulations (INEN, 2012; 1028-1034 g/cm3), as well as the Dornic degrees (14, on average, °D). Taken together, these results confirm that the raw milk analyzed meets the established quality standards, ensuring a final product that meets regulatory expectations.
Table 1 shows the somatic cell count (SCC) values according to the sector of the El Chaco Canton. Statistically significant differences were reported between sectors (P < 0.001). In this case, the Linares sector showed higher SCC counts (5.69 log10; 491,124 cells/mL) when compared to the other sampling locations. SCC is a biomarker of udder immune status that directly reflects the quality of the final product, but it is often influenced by factors such as herd management practices, stage of lactation, and breed. In general, the Ecuadorian standard NTE INEN 9;2012 establishes a value of ≤ 700,000 cells/mL, which means that the analyzed samples are within the limits allowed to be considered acceptable quality milk.
Figure 1 shows the interaction between the experimental period and lactose and SCC content. It is evident that in sectors such as Linares, lactose content increased progressively (4.18 vs. 5.23 ± 0.5%), while in Tres Cruces, these values decreased drastically by the fourth period (4.47 vs. 3.91 ± 0.5%; P < 0.001). Regarding SCC, the Santa Rosa, El Chaco, Bombón, Cascabel, and Sardinas sectors showed moderate fluctuations throughout the experimental period. Therefore, this behavior could indicate possible differences in milking practices or the physiological state of the animals.
The results for antibiotic residue detection are shown in Table 2. Of the 500 samples analyzed, 495 tested negative for antibiotic residues in milk, representing 99% of the samples. Therefore, with this high percentage of negative samples, we can infer that most of the raw milk is free of pharmaceutical contaminants, which is a positive indicator for food safety and compliance with current national health regulations. Although only 5 samples, equivalent to 1.0%, tested positive for antibiotic residues in milk, in this case, the presence of beta-lactams, sulfonamides, and tetracyclines was specifically detected. Despite this low percentage of positive samples for antibiotics in milk, we are still concerned about the negative effects of antimicrobial resistance, as well as its repercussions on the yields of dairy products.
4. Discussion
The evaluation of the physicochemical parameters of raw milk in the El Chaco canton revealed that, in most cases, the levels of fat, protein, and solids align with the established NTE INEN standards. However, the slight deviations observed in some samples underscore the need for continuous and more rigorous monitoring (Salguero, 2019). These variations, although not widespread, may be indicative of factors that could influence the results, such as forage quality, livestock management, or possible failures in milk preservation processes (Guamán-Rivera et al., 2024). A study conducted by Duchi Yaguachi et al. (2023) in the province of Chimborazo analyzed raw milk samples from dairy industries and collection centers, reporting a 4% non-compliance rate according to INEN Standard 9:2012 for parameters such as temperature, density, percentage of fat, protein, and total solids (INEN, 2012). Therefore, to guarantee a homogeneous, high-quality product, it is essential that producers implement more rigorous quality control systems, as well as handling practices that ensure consistency in the physicochemical composition of the milk (Cajamarca, 2022). This will not only allow them to comply with legal regulations but will also strengthen consumer confidence and improve the product's competitiveness in the market (Salazar Rodríguez, 2023).
An evaluation of raw milk sold in the El Chaco canton determined that the physicochemical parameters comply with the NTE INEN 9 standard. However, differences were observed across sectors in nonfat solids, density, Dornic grades, and SCC, associated with factors such as diet, genetics, health management, hygiene, and production conditions. Studies from Europe, Asia and Africa have reported variable prevalence of antibiotic residues in raw milk, with frequencies ranging from <1% to >20%, depending on legislation, enforcement and farm management practices. These international data highlight that, although the 1% prevalence observed in our study is relatively low, the presence of any non-compliant samples is still relevant from a One Health perspective (Madougou et al., 2019; Vieira-Costa et al., 2024).
On the other hand, the results obtained show that a higher non-fat solids content is associated with a lower somatic cell count, which is an indicator of a lower incidence of mastitis and other mammary infections (Rainard and Riollet, 2006; Salama et al., 2020). Non-fat solids showed significant variations, with higher values in Linares, Bombón, and Cascabel, while Tres Cruces had a lower concentration. These differences are related to the nutritional quality of the diet, forage availability, and energy-protein balance factors that influence the synthesis of proteins, lactose, and minerals present in milk. Density showed a pattern similar to that of non-fat solids, with higher values in Linares and Cascabel. This indicates an association with the concentration of dissolved components in milk and reflects natural changes in chemical composition. Dornic grades also varied across sectors, although they remained within established ranges.
This finding is particularly important, since a high somatic cell count not only deteriorates milk quality but is also directly related to economic losses due to reduced livestock productivity. (Lima-Rodríguez et al., 2022). Furthermore, the microbiological quality of milk is intrinsically linked to the somatic cell count, reinforcing the importance of maintaining an adequate level of non-fat solids (Alhussien and Dang 2018; Guamán-Rivera et al., 2024). A balanced composition in terms of non-fat solids contributes to milk stability, improving its shelf life and sensory properties (Rassu et al., 2007; Duangjinda et al., 2016).
Proper feed management and animal welfare are key to optimizing milk composition, which in turn is reflected in improved animal health and the quality of the final product. (Puga-Torres et al., 2024). Somatic cell count analysis in raw milk revealed high variability among samples, reflecting significant differences in the udder health of the cattle (Alhussien and Dang 2018). SCC differed across sectors, with Linares standing out as having the highest value, although still within the permitted limit. This indicator reflects udder health and may be related to mastitis, milking hygiene, and health management. The results highlight the need to strengthen prevention, monitoring, and technical assistance programs to improve milk quality. An elevated somatic cell count is an indicator of mastitis, an inflammatory disease that affects milk quality and cow productivity (Malek dos Reis et al., 2013; Li et al., 2014; Kirkeby et al., 2020). The observed variability suggests that not all dairy farms are applying the same prevention and treatment measures, resulting in inconsistent final product quality (Guamán-Rivera et al., 2024). Mastitis, in addition to reducing the microbiological quality of milk, can have significant economic consequences (Qolbaini et al., 2014; Ndahetuye et al., 2020), including decreased production and the need for costly treatments (Baltián et al., 2023).
Herd health is fundamental to high-quality milk production, and regular somatic cell count (SCC) monitoring should be standard practice on all farms (Kirkeby et al., 2020; Millogo et al., 2009). Ecuador and Brazil differ notably in their regulatory limits for raw milk quality, particularly for SCC, with Ecuador allowing a higher maximum SCC than Brazil. Ecuadorian standards (INEN, 2012) set an upper limit of 700,000 somatic cells/mL, which is considered relatively lenient compared with international benchmarks such as the European Union’s threshold of 400,000 cells/mL (Puga-Torres et al., 2022). In contrast, Brazilian regulations (Normative Instruction 51/2002 and subsequent updates) establish a stricter maximum SCC of 500,000 cells/mL for refrigerated raw bovine milk, although this value still exceeds the EU limit (Bruzaroski et al., 2017).
These regulatory differences reflect distinct national approaches to udder health and milk-quality control, with Brazil adopting tighter SCC thresholds than Ecuador but still departing from the most stringent international standards. Implementing comprehensive programs for udder health management, including preventative practices, early diagnosis, and effective treatment, is key to reducing somatic cell count variability and improving overall milk quality (Guamán-Rivera et al., 2024). Furthermore, it is important to encourage the adoption of real-time monitoring technologies, which allow producers to identify health problems in cows before they significantly impact milk production, thus ensuring better product quality and the sustainability of dairy farms (Curi Calla, 2019).
Anyhow, when compared with regulatory limits and typical values reported in other regions, the mean composition observed here is broadly similar. For example, European Union and North American standards generally require minimum protein contents of 2.9-3.0% and fat contents around 3.5-3.7%, with SCC thresholds commonly set between 400,000 and 750,000 cells/mL.
Regarding the presence of antibiotics in milk, significant variability was observed in the presence of these residues among the different samples analyzed, suggesting inconsistencies in the management and administration of veterinary treatments on livestock farms. This variability highlights the urgent need to establish stricter and more uniform controls on the application of antibiotics, as well as on monitoring the recommended withdrawal periods before milk is marketed. The detection of antibiotic residues in 500 milk samples from the El Chaco canton yielded 495 negative results and 5 positive results (1%) for β-lactams, sulfonamides, and tetracyclines. Because qualitative screening methods were used, these results represent surveillance alerts and do not constitute definitive confirmation of regulatory noncompliance. Accurate identification requires quantitative techniques that determine concentrations and compare them to maximum permitted limits. Although the frequency was low, it is important to strengthen monitoring, provide training to producers, and promote best practices in the responsible use of veterinary drugs to ensure milk safety.
Similar results were observed in the study by Matailo Fernández et al. (2023) who, in 116 samples analyzed, detected 2 cases of antibiotic residues (1.8%), both positive for beta-lactams and sulfonamides. In contrast to these results, in the Naranjal canton of Guayas province, 14 out of 72 samples analyzed tested positive (19.4%) for beta-lactams (11 samples) and for a combination of beta-lactams and sulfonamides (3 samples) (Aroca, 2016). Similarly, a study in southern Quito reported that of 96 samples analyzed, only 9 (9.38%) were suitable for human consumption (Luje-Pilapanta, 2021).
Therefore, non-compliance with these practices not only poses a risk to public health but can also lead to financial penalties for producers, affecting the viability of the supply chain (Herrera Araya, 2021). It is important to understand that the presence of antibiotic residues at levels exceeding permitted limits could also contribute to the development of antimicrobial resistance, a global problem that compromises the effectiveness of medical treatments in both humans and animals (Ayukekbong et al., 2017; Maron et al., 2013; Hedman et al., 2020; FAO, 2021). Therefore, it is essential to implement continuous monitoring programs with training for producers on the proper use of antibiotics, as well as promote rapid detection methods and regular testing at collection centers to ensure that raw milk meets the quality standards of the INEN regulations. (Quispe et al., 2021).
5. Conclusions
This study provides new evidence on the quality and presence of antimicrobial residues in raw milk sold in the Ecuadorian Amazon using a longitudinal approach that has been little documented in the region. The results show that, although the compositional quality is generally acceptable, there remains an occasional risk of antibiotic residues, highlighting the need for continuous monitoring. The use of low-cost screening methods proved to be a practical and applicable tool in rural settings with limited resources. These findings are relevant for the design of health monitoring programs, the training of producers, and the strengthening of public policies aimed at food safety and public health.
Acknowledgements
To ESPOCH, Sede Orellana for lending us the facilities for this study.
Data Availability Statement
The data from this research may be requested from the principal author by sending a letter explaining the reasons for the request.
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Editor:
Takako Matsumura Tundisi
