Dairy goats in Europe are most common around the Mediterranean basin, and the main use of the milk is for cheese making (Ruiz-Morales et al., 2019). The quality of the milk required for cheese making depends on its physical, proximate chemical, and hygienic-sanitary characteristics; for example, total bacterial count (BC) and somatic cell count (SCC) Pirisi et al., 2007). Traditionally, quality assessment systems consider several parameters, such as cheese extract (protein and fat percentages) and hygienic and bacteriological quality (Pirisi et al., 2007).

In recent years, foods containing natural antioxidants in general, and milk and dairy products in particular, have been demanded by consumers for their beneficial health effects in both humans and animals (McGrath et al., 2018; Khan et al., 2019). In animals, important roles for antioxidant compounds in maintaining optimum udder health have been identified (O`Rourke, 2009; McGrath et al., 2018). In this regard, the total antioxidant status in milk has been correlated with udder health, as reflected by the number of somatic cells present in milk. The total antioxidant capacity (TAC) is lower in mastitis milk samples compared with normal milk in cows (Atakisi et al., 2010) and in goats (Silanikove et al., 2014). However, studies on milk production, commercial traits, and total antioxidant status in dairy goat farms are scarce and incomplete (Delgado-Pertíñez et al., 2013). Thus, the applicability of the results obtained from commercial flocks to modify milk composition and quality is not well established.

The autochthonous Payoya breed is a dairy goat raised in pastoral systems. At the time of the study, 28 flocks, and 8,178 Payoya goats were registered in the correspondent herd-book (Association of Payoya breeders; unpublished data). The average milk production of the breed is 440 kg in 219-days lactation (ARCA, 2011). Produced milk is mainly oriented towards the production of pure goat cheeses. As in other small ruminant farming, their economic efficiency is mainly conditioned by productivity and feeding management (Milan et al., 2003; Ripoll-Bosh et al., 2012¸ Mena et al., 2017). The researchers’ previous work (Gutiérrez-Peña et al., 2016; Mena et al., 2017), in which the profitability and social data of Payoya goat systems have studied, has suggested actions to enhance the viability of farms, such as commercial strategies to improve the sales of their products, for example, through specific certification. In this regard, a national regulation for commercializing native-bred animal products (Royal Decree-Law RD 505/2013) with a logo (“100% Raza Autóctona”) has been published. This logo affects many products, including those fresh or processed from animals of autochthonous breeds (meat, milk, eggs, derivatives, and even non-food products such as wool).

Currently, consumers demand more information about the quality and origin of the products they purchase, making it necessary to establish specific identification by labeling products from autochthonous breeds. Therefore, using the above-mentioned national regulation will require assessing the quality of a farm’s products. Based on previous work, milk samples from three grazing-based management groups were analyzed for fatty acid profile and vitamin A and E contents. There were few differences between groups, but important differences were found according to the season (Gutiérrez-Peña et al., 2018). However, there is a lack of information comparing the effect of Payoya management systems on commercial milk quality parameters.

Mena et al. (2017) conducted a multivariate analysis of the economic and social parameters of sixteen Payoya goat farms under conventional grazing-based management systems in southwestern Spain and identified three clusters. The primary aim of the present work was to provide an overview of the commercial traits and antioxidant composition of milk produced on those farms. These results would contribute significantly to the national regulation for the commercialization of native-bred animal products. A second aim of the current work was to assess the relationships between the antioxidant content and the hygiene-sanitary parameters in milk.

The indicators of feeding management are shown in Figure 1. The NERG was not statistically different between the more pastoral farms (LPG and HPG clusters; average 47%), but these values were higher (p<0.001) than that obtained for the MIG farms (19%; Figure 1a). Moreover, the MIG farms showed a higher (p<0.001) goat feed supply based mainly on concentrates (1.3 and 0.4 kg d⁻¹ for concentrate and forage supply, respectively), and no differences were found between the LPG and HPG farms (averages of 0.8 and 0.1 kg d⁻¹ for concentrate and forage supply, respectively). The amount of feed provided also changed with the month (Figure 1b). In winter (December, January, and February) and autumn (September, October, and November) months, goats received the highest amounts of concentrate (average of 1.2 kg d⁻¹; p<0.05) because the intensity of grazing was lower, and births were concentrated in those seasons of the year. The forage contribution followed an analogous pattern, supplying maximum amounts when the animals grazed less.

The yield, chemical and hygiene-sanitary compositions, and economic parameters of the milk according to the goat grazing group are shown in Table 1. No statistical differences in the percentages of chemical parameters were observed between the groups studied. Nevertheless, daily yields of milk and milk components were not different (p>0.05) between the MIG and HPG groups (averages of 1.34 L d⁻¹ and 65.5, 49.8, and 61.8 g d⁻¹ of fat, protein, and lactose, respectively), but were higher (p<0.05) than those obtained in the LPG group (0.77 L d⁻¹ and 39.5, 28.7, and 37.1 g d⁻¹ of fat, protein, and lactose, respectively). Consequently, and although the price of milk was similar for all farms (0.52€ L⁻¹), the final milk income was higher (p<0.01) for MIG and HPG farms (average of 0.70€ per goat d⁻¹) than for LPG farms (0.40€ goat d⁻¹) (Table 1).

The yield, chemical composition, and economic parameters of the milk were affected by the sampling month (Tables 1 and 2; Figure 2). The highest milk yield was obtained in the spring (March, April, May) months, followed by the winter months of January and February, and the lowest values were found in autumn and at the end of summer. The patterns throughout the lactation months of the lactose percentage and yield were similar, while the fat and protein percentages had an inverse relationship (higher during the autumn and, secondarily, in winter), to milk yield. The price of goat milk behaves seasonally, reaching a maximum at the end of summer and during the autumn, when there is a production deficit on farms (Figure 2). Considering the price and yields of milk (Figure 2 and Table 2), the lowest milk income was obtained in the summer months and in November (Figure 2).

The BC and SCC of the milk showed no significant differences (p>0.05) with respect to the groups studied (Table 1) but were affected by the sampling month (p<0.001, Table 2). The highest SCC and BC were obtained at the end of summer and autumn, while the remaining months had the lowest counts.

Regarding the relationship of milk yield and chemical parameters with the hygiene-sanitary composition, as the SCC increased, milk yield (r = −0.23, p<0.01) and lactose (r = −0.40, p<0.001) decreased, whereas fat (r = 0.29, p<0.001) and protein (r = 0.50, p<0.001) contents increased. A positive correlation was obtained between SCC and BC (r = 0.26, p<0.001).

The TAC did not vary significantly (p>0.05) between the groups studied (Table 1). Nevertheless, it was significantly higher (p<0.001) in winter and spring milk than in milk samples taken during other seasons (Table 2). Regarding the relationship between the hygiene-sanitary parameters and the TAC, a negative correlation (r = −0.30, p<0.001) between TAC and SCC was found.

Although all animals in the study were fed by grazing, the contribution of grass differs between groups. Mena et al. (2017) have observed that the HPG farms have similar milk production per goat to the MIG farms and greater productivity than the LPG farms, with similar NERG and concentrate and forage inputs. According to milk production and chemical composition, the levels of energy and protein provided by grazing and supplemental feeds would be similar in the HPG and MIG groups and higher than in the LPG group (Morand-Fehr et al., 2007). In the present study, milk sales are the main income (Mena et al., 2017), and according to the current pricing system (including prevailing penalties), the differences between the groups are due to the milk productivity (L d⁻¹) because there were no differences in either the cheese extract (protein and fat percentages) or in the SCC and BC (Table 1).

Milk yield (1.20 L d⁻¹) was smaller, and the percentages of basic chemical components (5.00%, 3.69%, and 4.44% for fat, protein, and lactose, respectively) were within the range of individual test-day data from Murciano–Granadina goats (Pleguezuelos et al., 2015), the most important Spanish dairy goat breed, reared under a semi-intensive system, and of the bulk tank milk from dairy goat farms (de la Vara-Martínez et al., 2018). The reduced yield in the study area may be due to the characteristics of the farming systems, specifically to the autochthonous Payoya breed, which are well adapted to grazing but farmed less intensively and, consequently, have lower milk productivity. Stage of lactation and feeding (mainly due to ingestion and nutritive value of the feedstuff) differences can explain the milk yield and composition results in the months analyzed (Delgado-Pertíñez et al., 2013). Regarding the physiological factor of lactation, in the farms of this study, lactation finished toward summer, and the main kidding period was in autumn. Together with the lower temperatures, this would partially explain the reduced milk production and enriched chemical composition at the end of summer and autumn. The reproduction pattern of those farming systems (births are concentrated in October–November and January–February) is made to graze the most in spring and reduce the number of lactating animals in summer, when pasturage is scarce in the Mediterranean region (Mena et al., 2017).

Bulk tank SCC and BC have been used as indicators to evaluate udder health, as well as the efficiency of production processes and cleaning and hygiene-sanitary practices (Delgado-Pertíñez et al., 2003; Gonzalo et al., 2010; de la Vara-Martínez et al., 2018). In this study, geometric means for SCC (1950 × 10³ cells/mL) and BC (77 × 10³ cfu/mL) were similar to values reported for bulk tank milk from the same breed (Delgado-Pertíñez et al., 2003) and other Spanish breeds (de la Vara-Martínez et al., 2018). Significant differences in the hygiene-sanitary quality of the milk were observed for different months, in agreement with a previous study of the same breed (Delgado-Pertíñez et al., 2003). However, no significant differences were found by de la Vara-Martínez et al. (2018) in other Spanish breeds, indicating that the results are more related to good farming practices.

The seasonal variation of the SCC in our study could be related to the lactation phase, increasing toward the end of lactation (Zeng et al., 1997; Raynal-Ljutovac et al., 2007), and other non-infectious factors (Raynal-Ljutovac et al. 2007). Higher counts due to physiological causes are common because several breeding females are present in the goat herds throughout the year, and postpartum and lactation periods occur successively (Raynal-Ljutovac et al., 2007; Gutiérrez-Peña et al., 2016). Furthermore, this indicator has been associated with intra-mammary infections and milk yield losses in dairy goats (Baudry et al., 1997; Pleguezuelos et al., 2015). Nevertheless, SCC levels in small ruminants have still not been included in European legislation (EC No. 853/2004) because their significance is still debatable. Unlike the milk yield in the present study, fat and protein percentages have been shown to rise as SCC increases, in agreement with previous studies in the same breeds (Delgado-Pertíñez et al., 2003) and other Spanish breeds (Pleguezuelos et al., 2015). Although a decrease in fat and protein is expected during intramammary infection due to the reduced synthetic and secretory capacity of the mammary glands (Raynal-Ljutovac et al., 2007), no studies have rigorously evidenced this phenomenon in goats (Pleguezuelos et al., 2015). The increases in these parameters observed in our study have also been reported by other authors (Barrón-Bravo et al., 2013; Pleguezuelos et al., 2015), who attributed it to a concentration effect associated with the reduction in milk yield in infected goats as inflammatory response increased. In the case of protein, a higher soluble protein concentration in milk from blood associated with a mammary infection or SCC (Leitner et al., 2004a,b) together with a concentration effect (due to decreased milk yield) could explain the higher correlation found for protein content compared to that for fat content as SCC increases.

Unlike SCC, BC is covered by EU legislation (EC No. 853/2004), with different thresholds set according to the species and the intended use of the milk. The limits for milk from species other than cow are ≤500×10³ cfu/mL when the destination of milk does not include heat treatment or ≤1500×10³ cfu/mL for heat-treated milk before processing. In our study, the BC was lower in the months with the highest environmental temperatures; this requires the implementation of good hygiene-sanitary practices on farms, including maintaining the refrigeration tank at the correct temperature. The higher counts in some months (mostly autumn) may be associated with rainfall and, consequently, dirtier animals (Delgado-Pertíñez et al., 2003). The mean bacteriological values obtained in this study were lower than the maximum levels permitted by EC Regulation for products made with raw milk, which shows that the appropriate conditions of hygiene-sanitary management are being maintained at the study farms.

Dairy products contain natural antioxidants, such as vitamins, oligosaccharides, peptides, and minerals (Khan et al., 2019) and appreciable amounts of phenolic compounds (Di Trana et al., 2015; Chávez-Servín et al., 2018; Delgado-Pertíñez et al., 2021). The TAC did not vary significantly between the groups studied, in agreement with previous work (Delgado-Pertíñez et al., 2013), probably due to the similar management of animals on all farms based on the use of pastures. According to several studies in cows (Clausen et al., 2009) and sheep (Virto et al., 2012), the main water-soluble antioxidants of milk are derived from the caseins and other low molecular weight compounds, which could explain the differences between results obtained in different months in this study (i.e., higher values in winter and spring milk than in the other milk samples). With respect to the latter compounds, a positive correlation (r = 0.31, p<0.001) was observed between the TAC and retinol in our previous study (Gutiérrez-Peña et al., 2018), in agreement with the higher content of vitamin A in winter milk in our work and the findings of Revilla et al. (2016) in cheeses. However, no significant correlations have been found by other authors (Lucas et al., 2008). Some vitamins, such as vitamin A, play an important role in supporting the immune system (Spears and Weiss, 2008), and this could be associated, at least partially, with the lower SCC observed in the present study, in which a negative correlation (r = −0.22, p<0.01) between SCC and retinol was also observed. Indeed, vitamin A content in blood has been associated with the udder health of dairy cows (Chew et al., 1982; LeBlanc et al., 2004), and dairy cows supplemented with that vitamin at the end of the prepartum period had lower SCC in postpartum milk (Agustinho et al., 2021). There are few studies in goats; therefore, further research is necessary to better understand how these parameters are affected by the hygiene-sanitary components and affect inflammatory markers, especially in individual animals.

No significant differences were found between clusters in the composition, hygiene-sanitary parameters, and antioxidant capacity of the milk studied, as the animals in all farms were similarly managed based on the use of natural pastures. However, significant changes were observed in the milk composition by calendar month because of lactation effects and differences in feeding regimens. The percentage of lactose and the milk component yields (g d⁻¹) patterns throughout the lactation months were similar, while the relationship between the fat and protein percentages was inverse to milk yield. During the end of summer and autumn months, the highest number of bacteria and somatic cells in the milk were observed, but the bacteriological count levels were below the legal limit set by EC regulations. The TAC was significantly higher in winter and spring milks than in the other milk samples.

The negative correlation between the antioxidant capacity and the somatic cells shows the important role of antioxidants in maintaining optimal udder health. One of the compounds involved in this antioxidant mechanism could be vitamin A due to the positive correlation between the antioxidant capacity and retinol determined in a previous study.

Finally, the information generated in this and previous studies on the quality of goat milk from the autochthonous Payoya breed will contribute to establishing the records of the traceability system to guarantee that the animal products obtained are of the native breed. All of this will help the consumer to easily identify these products and increase their demand, which will result in the conservation and promotion of the genetic heritage of these breeds and the foods derived from them.