The potential of feeding ewes with fresh or dehydrated sulla forage to enrich sheep cheese in molecular biomarkers of health quality

Take home Message The use of fresh or dehydrated sulla forage in dairy ewes feeding enhances the health properties of cheeses due to transfer of antioxidant molecules and polyunsaturated fatty acids (PUFA). Introduction Sulla (Sulla coronarium L.) is a widespread legume species used as fresh or preserved forage. It is well known the positive impact of fresh sulla forage (FSF) on performance of ruminants and quality of their products, linked to the moderate content of phenolic compounds, mainly condensed tannins (CT) (Piluzza et al., 2014). Moderate levels of CT (<6% DM) inhibit the complete ruminal bio-hydrogenation of dietary unsaturated fatty acids (FA), enriching the animal products with PUFA beneficial for human health. Moreover, FSF contributed to increase the content of antioxidant compounds, thus improving the antioxidant capacity of goat milk (Di Trana et al., 2015). Dehydration of FSF could be suitable to preserve these properties, that are greatly lost during the hay-making process. This research has compared the cheeses produced from milk of ewes fed with diets based on sulla hay (SH), pelleted dehydrated sulla forage (DSF), or FSF, evaluating their FA profile and antioxidant activity, and verifying the presence of biomarkers of health properties useful for traceability of fresh forage-based diets. Material and methods The individual daily milk from 10 primiparous (PRI) and 10 pluriparous (PLU) Valle del Belice ewes at 60 days in milk, divided into 5 homogeneous groups fed different diets in a partial 5×2 Latin square design with 5 groups and 2 periods, and the bulk milk of farming ewes fed only on natural pasture were used in 2 sessions of micro cheese-making to manufacture pressed-curd type cheeses. The experimental diets were: SHL = SH ad libitum (al); DSF2 = 2 kg/d of DSF + SH al; FSF2 = 2 kg/d of FSF + SH al; FSF4 = 4 kg/d of FSF + SH al; FSFL = FSF al. Concentrate was supplied at level of 800 g/d for PRI or 1,200 g/d for PLU. Cheeses were sampled at 48 h and analyzed for their physicochemical traits, including contents of FA, vitamins A and E and polyphenols, and for their antioxidant capacity (TEAC) and oxidative stability (POV and TBARs). The ability of cheese components to discriminate the ewes’ diets was also evaluated. Results and discussion The diet FSFL with exclusive fresh forage ad libitum, as that of grazing animals, was confirmed to greatly improve the health properties of cheese. Indeed, FSFL diet was responsible of increased amounts of antioxidant substances, as vitamins A and E and polyphenols, that induced a better oxidative stability, and enhanced the level of PUFA such as rumenic (C18:2c9t11), the main CLA isomer, and α-linolenic (ALA, C18:3n-3). In cheeses from DSF2, the contents of vitamin A and PUFA were higher than in SHL cheeses and comparable to cheeses from the diet with 4 kg of FSF, whereas ALA was detected at the same level of FSFL cheeses. Evaluating the possibility of using these health cheese components as biomarkers of animals’ diet, a promising role in differentiating cheese from animals fed fresh forage emerged for vitamin A and some FA such as C15:0iso, C18:1, C18:1t11, total PUFA, n-6/n-3 ratio, and especially for ALA and its ratio with linoleic acid (LA, C18:2n-6) (figure 1). Conclusion The results showed how dehydration was able to preserve the potential of fresh sulla forage also with regard to nutritional and health properties of dairy products. Thus, the use of dehydrated sulla pellets as alternative to hay in periods of limited pasture resources can contribute to enhance the antioxidant capacity and the FA profile of milk and cheese, with health benefits for consumers. Moreover, some PUFA, especially ALA and the LA/ALA ratio, exhibited an effective role as biomarker of health quality and could be used for traceability of feeding regime.