Composition, coagulation properties, and cheesemaking traits of sheep bulk milk as affected by individual and...

Extensive and semi-extensive dairy sheep farming are commonly regarded, from a societal perspective, as positive systems. However, animal well-being and productive performance may be compromised by specific methods adopted within those systems. In the present study, we investigated the effects of farming, pasture, and grazing descriptors on sheep milk composition, coagulation properties, and cheesemaking efficiency, as assessed from sheep bulk milk collected in semi-extensive farms. Bulk milk samples were collected from 47 commercial farms located in Sardinia, Italy, rearing flocks of the local Sarda breed. Sampling was conducted at 4 consecutive stages of lactation (months of January, March, May, and July) to account for seasonal variation in milk production. A total of 188 samples were analyzed for milk composition, milk coagulation properties, cheese yield (CY%), and nutrient recoveries (REC) in the curd. Farms were scored using 9 descriptors related to farming, pasture and grazing conditions. These descriptors were submitted to principal component analysis (PCA) and cluster analyses to investigate their interrelationships. Subsequently, ANOVA was performed to assess the effects of individual descriptors and descriptor-based clusters on milk traits. As expected, most milk traits were significantly affected by the stage of lactation, and a substantial proportion of total variance was attributable to the individual farm effect. Among individual descriptors, flock size significantly influenced protein-related traits: farms with small and medium flock size (fewer than 400 ewes in production) exhibited greater percentages of milk protein, casein, and protein retained in the curd. The average load at pasture, calculated as the ratio of flock size to total pasture area, significantly affected milk traits: high load at pasture (≥10.1 sheep/ha) was associated with increased milk pH, which in turn is related to longer rennet coagulation time and reduced curd firmness, indicating impaired coagulation aptitude. Farm management score significantly affected udder health markers, with lower bacterial cell score in farms with the best management. In addition, the presence of competitors on grazing areas (wild boars and deer) was associated with increased somatic cell score, suggesting that interspecific feeding competition may negatively influence milk quality. Pasture botanical composition also significantly affected cheesemaking efficiency. Flocks grazing predominantly on leguminous species (e.g., sulla and clover) exhibited greater protein and energy recovery in the curd compared with those grazing mainly on graminaceous. The PCA identified 2 main farm typologies, classified as cluster 1, "Extensive-large flock," and cluster 2, "Intensive-small flock." However, ANOVA revealed limited differences in milk traits, with the only significant effect observed for protein recovery, which was higher in intensive small flock farms. In conclusion, farming, pasture and grazing descriptors emerged as relevant tools to investigate the effects of semi-extensive systems on sheep milk traits, with direct implications for cheesemaking efficiency.