Modeling the relationships among technological properties of sheep individual animal factors, milk composition, and minerals using generalized additive mixed models

The dairy sheep industry faces ongoing challenges in optimizing cheese production and enhancing efficiency across different breeds. This study provides crucial insights into how breed-specific factors, lactation stages, parity, and milk composition, including mineral concentrations, affect cheese yield and nutrients recovery in the curd. The aims of this study were to characterize individual sheep milk samples for cheesemaking efficiency by measuring 3 cheese yield traits (%CY; fresh curd, TS, and water retained) and 5 recovery of nutrients traits (%REC; fat, protein, lactose, TS, and energy) and to examine how these traits change throughout the lactation, considering different sheep breeds, parities, and variations in milk composition and mineral concentrations. A total of 760 ewes from Massese and Comisana breeds were sampled during the morning milking at the National Association of Sheep Breeders nucleus farm (Tuscany, Italy). The application of generalized additive mixed models (GAMM) was a key element of this study, enabling a more nuanced analysis of complex relationships and nonlinear trends. The GAMM accounted for variations in breed and parity, which were included as parametric terms, as well as milk minerals, rennet coagulation time (RCT), sampling day, and interactions between DIM and milk yield (MY), fat and casein, and Ca and P, which were treated as smooth terms. This approach provided insights that would have been difficult to capture with traditional linear models. Results evidenced breed and parity-specific variations. Indeed, the Massese had overall lower cheesemaking efficiency compared with the Comisana ewes, and primiparous ewes had higher percentages of both %CY and %REC traits. The interaction between DIM × MY was less significant in the Comisana breed compared with the Massese, with notable effects only on protein and lactose recovery in the Comisana. The interaction between fat × casein was also breed specific and affected with different extent and patterns the cheesemaking traits between the 2 breeds. Longer RCT increased the water retained in the curd and reduced the recovery of TS and the individual recovery rates of the main milk components in both breeds. The effect of Ca × P was not always linear on the cheesemaking traits and between breeds. Overall, an increase of both Ca and P was associated with higher %CY and %REC, except for the recovery of fat and energy. High Na and Cl were detrimental for the cheesemaking process in both breeds, whereas the destabilizing effect of K was particularly notable on the fresh curd, curd TS and the recovery of protein from the Massese milk. These findings highlight that sheep breed and parity, alongside specific milk components and mineral concentrations, significantly affect cheesemaking efficiency, with important differences between the Massese and Comisana breeds. Efficient cheesemaking requires careful consideration of mineral concentrations, especially in terms of Ca, P, Na, Cl, and K, to optimize yields and nutrients recovery in the curd.