In India, with the expansion of the dairy industry, it has become essential for its future sustainability to identify and conserve indigenous cow breeds across different agro-climatic zones of the country. Consequently, scientists have focused attention on the Gangatiri cow, which is predominantly found in the eastern zone of Uttar Pradesh; particularly in the Ganga watershed areas of Allahabad, Mirzapur, Varanasi and Ballia, along the Ganga River and adjoining regions. Indigenous cow breeds capable of producing higher quantities of milk were often lost due to ill treatment by owners and poor management practices. As a result, their milk yield gradually declined, their condition deteriorated and over time these breeds became neglected and moved into the danger zone (Verma et al., 2018).In recent years, conservation-oriented research emphasizing productivity and quality traits of indigenous cattle under diverse environmental conditions has gained momentum to support sustainable dairy development (FAO, 2011; Smith et al., 2019).
       
Gangatiri is an indigenous cattle breed of India, recognized as a distinct breed by NBAGR-ICAR (Accession No. 03039). It is an important dual-purpose breed of North India, with an average daily milk yield ranging from 4 to 6 litres per day. The lactation length varies between 150 and 250 days, while the inter-calving period ranges from 14 to 24 months. The coat colour of the Gangatiri cow is dull white, with a black muzzle and medium-sized hump and dewlap. Gangatiri cattle are particularly important for small and marginal farmers and are mostly maintained in small herds (Singh et al., 2018).
       
Milk and milk products are excellent sources of essential nutrients and are often described as nature’s nearly perfect food. Dairy products, particularly fresh milk, are regarded as a complete food as they contain all essential nutrients required for human health (Hossain et al., 2013). Milk contains several bioactive compounds important for nutrition and health protection and serves as a source of macro- and micronutrients (Ceballos et al., 2009), including fat and protein, which enhance its nutritional and commercial value (Negash et al., 2012).

Among environmental factors, the type and safety of feed consumed by milking cows, along with seasonal variation, have a significant influence on milk safety. Seasonal variation is recognized as a major non-genetic factor influencing milk composition and microbial load through changes in temperature, humidity, feed availability and farm hygiene (Smith et al., 2019).
       
Milk-borne bacterial diseases in humans range from gastrointestinal disorders to more severe and sometimes fatal food-borne infections, creating both public health and economic concerns (Grace et al., 2020). Milk is highly nutritious and therefore particularly susceptible to microbial spoilage (Perin et al., 2019).
       
To the current understanding, limited research has been carried out to evaluate the influence of seasonal variations on the compositional and bacteriological quality of milk obtained from Gangatiri cattle. Information regarding how different seasons affect milk composition and microbial quality in this breed remains inadequate, particularly under prevailing management conditions. Therefore, the present research work was undertaken with the aim of elucidating the effect of seasonal changes on the compositional and bacteriological characteristics of milk from Gangatiri cattle.

The present experiment was carried out at SHUATS, Dairy farm, Prayagraj, U.P., India. The experiment was conducted for two years. Monthly mean temperature and humidity range of Prayagraj district is shown in Fig 1 and Fig 2. Highest and lowest monthly mean temperature being 34.4°C and 16.3°C. However, highest and lowest monthly mean humidity were 88% and 24%. Coordinates of latitude and longitude of Prayagraj was 25.4°N and 81.84°E with an elevation of around 100 m above mean sea level. Humid sub tropical climatic conditions prevail in Prayagraj district of India (India Meteorological Department (IMD) (Station: Allahabad/Bamrauli).




 
Experimental animals
 
The animals were first screened using the Californian Mastitis Test and twelve Gangatiri cows showing negative results were selected for the study. All experimental cows were of the same breed and were maintained in a tail-to-tail housing system and kept under nearly similar managerial conditions throughout the experimental period. Uniform management and feeding practices were followed at the cattle unit farm. Gangatiri cows were fed according to the prescribed feeding schedule. Concentrate feed was offered individually to each cow during morning and evening milking in accordance with their maintenance and production requirements. As a thumb rule, for every 3 kg of milk produced, animals received 1 kg concentrate mixture along with dry roughage in the form of wheat straw and green fodder based on availability (Green Maize, Green Jowar and Berseem) was provided. Adequate health care measures were ensured to safeguard the animals against epidemics and incidental occurrences of illness.
 
Milk collection and analysis
 
Prior to milk sampling, hygienic measures were strictly followed, including clipping of long hair around the udder and flank, grooming, washing of the hindquarters, cleaning of the udder with a towel soaked in 2% Dettol solution and tying of the tail to the legs. Milking was carried out using the full-hand dry method. The initial two streams of foremilk from each udder quarter were discarded, after which 200 ml of milk was collected directly into sterilized conical flasks and immediately plugged. The collected samples were then transported to the laboratory for further analysis.
       
Milk samples were analyzed for fat, solids-not-fat (SNF), total solids (TS), water content, specific gravity and acidity percentage following standard procedures described by AOAC (1995). Microbiological examination of milk for standard plate count (SPC), lactic acid bacterial count, proteolytic bacterial count, lipolytic bacterial count and coliform count per ml of milk was carried out. The data obtained were statistically analyzed using analysis of variance (ANOVA) as described by Snedecor and Cochran (1994).

Factor for study
 
The experimental period was stratified into three seasons according to local climatic conditions: winter (November-February), summer (March-June) and rainy (July-October). This seasonal categorization was employed to examine the effect of seasonal variation on the parameters under study.
 
Parameters of study
 
Compositional quality
 
For the present experiment, the compositional Quality of milk was evaluated by determining major physicochemical parameters using standardized laboratory methods. These parameters included fat content, solid-not-fat (SNF), total solids (TS), water content, titratable acidity and specific gravity, which together describe the compositional characteristics of milk.
 
Bacteriological quality
 
The bacteriological Quality of milk was assessed by enumerating important microbial indicators associated with milk hygiene and quality. Standard plate count (SPC), lactic acid bacterial count (LABC), lipolytic bacterial count (LBC), proteolytic bacterial count (PBC) and coliform count were estimated using established microbiological techniques.

Compositional quality
 
The compositional Quality of milk, namely fat percentage, solids-not-fat (SNF) percentage, total solids (TS) percentage, water percentage, acidity percentage and specific gravity, were determined and are presented in Table 1 and graphically illustrated in Fig 3.




       
The one of the most important components of milk is fat. Fat content not only directly influences the nutritional value of milk but also affects its sensory characteristics, such as flavor and aroma. Furthermore, the quality of milk products including cheese, butter and cream largely depends on both the quantity and quality of fat present in the original milk. The fat content of raw milk is of considerable importance, as many dairy processing units determine the price of milk primarily on the basis of its fat content. In the present study, the highest mean milk fat percentage was observed during the winter season (5.08%), followed by the rainy season (5.06%) and the summer season (5.02%). However, the seasonal variation in milk fat content was statistically non-significant. The overall mean fat percentage across all seasons was recorded as 5.05%.Similar results were also observed by Sharma et al., (2001), Verma et al., (2010) and Bahashwan (2014). Comparable findings were also reported by Admasu et al. (2019), who observed that the fat content of milk was lower during the summer season compared to other seasons, while the highest milk fat content was recorded in winter. Leila Nateghi et al., (2014) reported milk fat contents of 3.39% and 3.41% during summer and winter seasons, respectively, with the seasonal difference being statistically non-significant (p>0.05).
       
Solid-not-fat (SNF) represents the major milk constituents other than fat, including proteins, lactose and minerals and is an important indicator of milk nutritional quality. In the present study, the highest mean solid-not-fat (SNF) percentage was recorded in milk produced during the winter season (9.27%), followed by the rainy season (9.13%) and the summer season (8.88%). The observed seasonal differences in SNF content were statistically significant. The overall mean SNF percentage across all seasons was 9.09%.Similar results were also reported by, Verma et al., (2010).
       
One of the important parameters used to evaluate milk quality is total solids (TS) content, which represents the amount of solids present in milk. Higher TS content indicates better nutritional quality of milk, as it reflects a greater concentration of valuable components such as proteins, fats, minerals and other micronutrients. In the present study, the highest mean total solids (TS) percentage was recorded in milk obtained during the winter season (14.35%), followed by the rainy season (14.19%) and the summer season (13.90%). The seasonal differences in TS content were statistically significant. The overall mean TS percentage across all seasons was observed to be 14.14%.Similar result was also observed that Verma et al., (2010) and Verma et al., (2018).
       
Water content in milk is inversely related to total solids and reflects the dilution effect due to seasonal and physiological factors. In the present study, the highest mean water percentage in milk was recorded during the summer season (86.01%), followed by the rainy season (85.82%) and the winter season (85.65%). The seasonal variation in water content was statistically non-significant. The overall mean water percentage across all seasons was 85.82%.Similar result was also reported (Mayilathal et al., 2017).
       
Acidity of milk is an indicator of freshness and microbial activity and is influenced by environmental temperature and hygienic conditions. In the present study, the highest mean acidity percentage was observed in milk produced during the rainy season (0.15%), followed by the summer and winter seasons, both recording a mean value of 0.14%. The seasonal differences in milk acidity were statistically significant. The overall mean acidity percentage across all seasons was observed to be 0.143. Similar results were also found that the significant seasonal variation in the acidity of cow milk under organized and unorganized dairy farming conditions in Uttar Pradesh (Verma and Singh 2018). The higher acidity during the rainy season may be associated with increased microbial activity under humid environmental conditions (Gupta et al., 2020).
       
Specific gravity of milk is an important physical parameter that reflects the concentration of milk solids, particularly SNF. In the present study, the highest mean specific gravity of milk was recorded during the winter season (1.030), followed by the rainy season (1.029) and the summer season (1.028). The seasonal differences in specific gravity were statistically significant. The overall mean specific gravity across all seasons was observed to be 1.029.Similar results were also reported by (Verma et al., 2018) observed that seasonal variations significantly influenced the specific gravity of cow milk.

Bacteriological quality
 
The bacteriological Quality of milk, namely standard plate count (SPC), lactic acid bacterial count (LABC), lipolytic bacterial count (LBC), proteolytic bacterial count (PBC) and coliform count, were estimated and are presented in Table 2 and graphically illustrated in Fig 4.




       
Standard plate count (SPC) reflects the bacteriological quality of milk and total viable bacterial load and may vary with seasonal changes. In the present study, the highest mean SPC (10⁴)/ml was recorded as 260.58 in milk of cows of summer season followed by 259.75 in milk of cows in rainy season and 235.42 in milk of cows in winter season respectively, the differences in these were non-significant. The overall mean SPC was recorded as 251.92 ×10⁴ /ml. Similar result were also reported by (ISO 4833-1, 2014 described that SPC is a standard microbiological indicator used to estimate the total viable bacterial load in raw milk and is widely applied for assessing milk hygiene quality. Hayes et al., (2001) reported that higher SPC values are mainly associated with poor milking hygiene, contaminated equipment and improper storage conditions.
       
Lactic acid bacterial count (LABC) represents beneficial micro flora involved in milk fermentation and quality and may vary seasonally. In the present study, the highest mean LABC (10³)/ml was recorded as 35.08 in milk of cows of summer season followed by 26.92 in milk of cows in rainy season and 23.33 in milk of cows in winter season respectively, the differences in these were non-significant. The overall mean LABC was recorded as 28.44×10³/ml. (Haug et al., 2007) observed that the lactic acid bacteria are natural components of raw milk microflora and their presence reflects microbial balance impacted by handling, temperature and storage conditions. They further reported that environmental and processing factors significantly affect the population of beneficial bacteria in raw milk.
       
Lipolytic bacterial count (LBC) indicates fat-degrading microorganisms in milk and is influenced by seasonal conditions. In the present study, the highest mean LBC (10²)/ml was recorded as 16.67 in milk of cows of summer season followed by 12.25 in milk of cows in rainy season and 9.92 in milk of cows in winter season respectively, the differences in these were significant. The overall mean LBC was recorded as 12.94×10²/ml. Similar result were also reported by Rameshwar et al., (2022), observed that lipolytic bacterial count in raw milk varied significantly with milking time, with higher values in noon and evening milk than morning milk. The differences in these values due to milking time were found significant.
       
Proteolytic bacterial count (PBC) reflects protein-degrading microorganisms in milk and may vary with season. In the present study, the highest mean PBC (10²)/ml was recorded as 21.25 in milk of cows of summer season followed by 19.92 in milk of cows in rainy season and 18.58 in milk of cows in winter season respectively, the differences in these were significant. The overall mean PBC was recorded as 19.92×10²/ml. similar result were also reported by (Rameshwar et al., 2022) reported that bacterial loads in raw milk are significantly higher during summer months, validating the seasonal trend found in this study. Furthermore, (Aslam et al., 2015) reported that proteolytic strains escalate in warmer seasons when environmental heat accelerates microbial proliferation.
       
Coliform count indicates the hygienic quality of milk and may vary seasonally. In the present study, the highest mean coliforms/ml (1.58) was recorded in the milk of cows during the rainy season, followed by 1.08 in the summer season and 0.50 in the winter season, respectively. The differences among seasons were significant and the overall mean coliform count was recorded as 1.06/ml. similar results have many researcher observed that the primary sources of coliforms include faeces, litter and the surfaces of improperly cleaned milk equipment and devices. Coliform bacteria are also known mastitis pathogens (Alemu and Abraha, 2017) and in cases of coliform mastitis, milk production may be reduced, leading to economic losses on farms (Mbuk et al., 2016). Coliform bacteria are considered faecal indicator microorganisms and are generally present in the environment; therefore, their presence in food indicates contamination (Mhone et al., 2011; Wanjala et al., 2018). These bacteria may also occur in the dairy farm environment, including milking equipment, dirt, faecal sources and water (Kagkli et al., 2007). The bacteriological quality of raw milk is also influenced by seasonal conditions and hygienic management practices during milk production and handling (Kumar and Mandal, 2023).

The study had season-driven variations marked influence on both the compositional and bacteriological quality of milk from Gangatiri cattle. Fat percentage showed a non-significant seasonal variation, whereas solids-not-fat, total solids, acidity and specific gravity were significantly affected by season, with higher values observed during the winter season. Water content was recorded highest during the summer season.
       
Further, standard plate count and lactic acid bacterial count showed non-significant seasonal variation, although higher counts were observed during summer and rainy seasons. In contrast, lipolytic, proteolytic and coliform counts were significantly influenced by season, recording higher values during summer and rainy seasons. Basically, the winter season was found to be the most favorable for better compositional and bacteriological quality of milk. These findings provide baseline information on season-driven variations in milk quality of Gangatiri cattle and emphasize the importance of adopting season-specific management and hygiene practices.

All authors declare that they have no conflict of interest.