# Assessment of Milk Quality in Skopelos Goats Under Low- and High-Input Farming Systems
## 3 Results
### Principal Component Analysis (PCA)
However, in the second and third LSs, 2023 showed significantly lower yields compared twitho 2022, followed by an improvement in the fourth LS in 2023 (\(p<0.001\)). Figure 4: Effect of the lactation stage on milk yield and chemical composition. (**a**) am_milk yield; (**b**) fat; (**c**) protein; (**d**) lactose; (**e**) total solids; (**f**) caseins. Significance levels: ns = not significant (\(p\geq 0.05\)); **= \(p<0.01\); *** = \(p<0.001\). Figure 3: Effect of farming system (extensive vs. intensive) on milk yield and chemical composition. (**a**) milk yield; (**b**) fat; (**c**) protein; (**d**) lactose; (**e**) total solids; (**f**) caseins. Significance levels: ns = not significant (\(p\geq 0.05\)); **= \(p<0.01\); *** = \(p<0.001\). In the intensive system, milk yield was consistently higher in 2023 across the second, third, and fourth LSs (\(p<0.001\)), suggesting improved productivity over time. However, the fluctuations observed between the years seemed to diminish in the fourth LS, where the differences became less pronounced. In both farming systems, fat content remained relatively consistent across most lactation stages (Figure 5b). In the extensive system, no significant year effect was observed during the first and third LSs, while lower fat percentages in 2023 were recorded in the fourth LS (\(p<0.01\)). In the intensive system, significant year-to-year differences were found in the first, second, and fourth LSs (\(p<0.01\)), whereas no year effect was detected in the third LS. Protein content was significantly affected by the year across all lactation stages in both farming systems (\(p<0.001\)). In the extensive system, protein levels declined progressively as lactation advanced, decreasing from 3.75% in the first LS of 2022 to 3.56% in the fourth LS. A similar trend was observed in 2023, with values dropping from 3.63% to 3.36%. In the intensive system, protein content started at 3.71% in the first LS of 2022, declining to 3.24% in 2023. A further reduction was evident in the second LS, with values dropping from 3.54% in 2022 to 3.40% in 2023. However, in contrast to the early lactation stages, protein levels stabilized or increased slightly in the third and fourth LSs. In particular, the fourth LS in 2022 showed an increase of 0.19%, while in 2023 it rose by 0.09% from the third LS, suggesting a potential compensatory effect in late lactation (\(p<0.001\)) (Figure 5c). Lactose content showed a greater sensitivity to year \(\times\) LS interactions, followed by a consistent downward curve, corresponding with the decline in milk yield (Figure 5d). Regarding TSs (Figure 5e), a gradual decline was observed as lactation progressed, with the extensive system consistently showing slightly higher values than the intensive system across all stages. While both systems followed a similar downward trend, no significant year-to-year differences were observed during the early lactation stages (first and second  
Figure 5: Chemical composition of milk across the four LSs within farming systems (extensive and intensive) over the two years (2022 and 2023). (**a**) am_milk yield; (**b**) fat; (**c**) protein; (**d**) lactose; (**e**) total solids; (**f**) caseins. Within each farming system and milk trait, means were compared across lactation stages. Significance levels: NS = not significant (\(p\geq 0.05\)); * = \(p<0.05\); ** = \(p<0.01\); *** = \(p<0.001\). LSs). The differences between years became more noticeable only in later stages, but the overall pattern of decline remained consistent across systems and years. Casein levels (Figure 5f) in the extensive system declined progressively as lactation advanced. A significantly lower casein content was observed in 2023 compared with 2022 during the first, second, and fourth LSs (\(p<0.001\)). In contrast, the intensive system exhibited more fluctuation in casein levels across the lactation stages rather than a steady decline.