Herbaceous feed and quality dairy production in Sardinian sheep farms: a short supply chain approach

Mediterranean agro-silvopastoral systems are increasingly recognized as a key resource for livestock feeding and welfare, for producing healthy and certified products, as well as for providing ecosystem services and a mosaic of landscapes. Unsustainable food supply chains can lead to increasing climate change impacts, depletion of natural resources and other critical effects on environmental media (Crippa, M., 2021). The intake of fresh herbage results in the presence of milk molecules that can have positive effects on human health, such as certain vitamins, phenolic compounds, and polyunsaturated fatty acids (Cabiddu et al., 2022). Driven by growing interest in production methods and environmental issues, consumers favor dairy and meat products from pasture-based diets, recognizing the enhanced organoleptic, health, and sensory qualities resulting from herbage consumption (Gutierrez-Peña et al., 2021). However, competitiveness and the intensification of production processes should be supported by improving the quality of the products offered and their added value. However, the competitive advantages of traditional, low-environmental-impact farming are counterbalanced by a lack of innovation, high production costs, poor traceability, and medium-low quality, which are the key factors negatively impacting the economy of our agro-silvopastoral systems. Some of these challenges can be addressed through management models that also emphasize health and environmental sustainability. The composition of dairy fat is strongly influenced by the ruminant’s diet. Linoleic acid and α-linolenic acid are the main fatty acids that are mostly modified by anaerobic bacteria in the rumen via a biohydrogenation process aimed at producing saturated fatty acids. In particular, the intake of fresh forages can increase the concentration of polyunsaturated fatty acids ω-3 and ω-6 and conjugated linoleic acid in milk and cheese, compared with diets based on dry forage or concentrates (Nudda et al., 2014). Indeed, the high diversity of Mediterranean flora and the legume-based swards provided by improved pastures, represent a valuable source of components characterized by high nutritional value, such as phenolic compounds, fatty acids and vitamins that have been shown to exert antioxidant activities against several pathologies induced by oxidative stress (Re et al., 2019). Aiming to address these needs, the Sardinia Region's PROCASU and PEROLACRU Projects, both funded under the PSR (Rural Development Program 2014-2020 submeasures 16.2 and 16.1) and directed by the CNR ISPAAM of Sassari. The goal of the project was to develop new dairy products from a controlled and certified production chain, specifically focusing on producing traceable, locally sourced pecorino cheese tied to its production area. The activity included the introduction of innovative forage systems in various sheep farms of two dairies in Northern Sardinia (Mores and Pattada – SS), with the establishment of improved pastures based on selected pasture legumes, rich in biodiversity.To assess the impact of herbage-based feeding on the quality and traceability of Sardinian sheep milk, used in typical cheese production, the project explored the relationship between grazing, herbage quality, and the milk and processed products. Phenolic compounds and antioxidant capacity were evaluated in herbaceous samples. Total phenolics were measured using the Folin-Ciocalteu reagent (Re et al. 2019). Antioxidant capacity was evaluated by ABTS ((2,2’- azinobis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt)) assay (Re et al., 2019); the results were expressed in terms of Trolox equivalent antioxidant capacity (TEAC), as (mmol TEAC 100 g−1 DW). Analyses of individual phenolic compounds in plant species were carried out using an Agilent 1260 series HPLC instruments. The bulk milk samples from different farms were analysed through physico-chemical analysis for the macro-composition, immune-electrophoretic and mass spectrometry techniques. The milk soluble fraction at pH 4.6 was analyzed using an LTQ Orbitrap and Orbitrap Exploris 120 for the metabolomic analysis. The lipid fraction was analyzed by GC-FID. Forage samples showed values of total phenolics ranged from 45.4 to 61.4 g GAE kg-1 DM and the antioxidant capacity varied from 5.30 to 6.35 mmol TEAC 100 g−1 DM. The differences depended on the specific pasture composition. Neochlorogenic, chlorogenic acids and quercetin glycosides were present across different farms. Forages rich in antioxidants could represent a more appealing option to farmers, as they offer a natural and economic option, while also possessing environmental benefits. Over the year, milk fatty acid composition showed a qualitative improvement. The milk protein quality profile provided a detailed overview of the chemical and protein variations in response to the animals' diet. The analysis of metabolic compounds revealed that the forage-based diet significantly influenced milk’s chemical composition, leading to changes in fat, protein, and other bioactive components. Casein fraction analysis confirmed ovine casein integrity and revealed genetic variants, including a 'silent' variant detected by mass spectrometry, which may serve as markers for specific breeds or regions, providing a detailed view of the milk's molecular composition. The stability and integrity of the casein fractions across all samples further emphasize the high quality of the milk, as degradation or breakdown of these proteins would indicate poorer quality or unfavorable conditions during milk processing. These findings offer valuable insights into the potential nutritional and functional properties of milk produced by sheep fed with a targeted diet.