POTENTIAL OF SULLA FORAGE (Sulla coronaria (L.) Medik) AS A TANNIFEROUS FEEDING RESOURCE FOR DAIRY EWES

Sulla is a legume species primarily used as forage, exploited mainly by grazing small ruminants during early spring, and then left ungrazed to constitute hay stocks. Fresh sulla forage is known to enhance the physiological status and the productive responses of dairy ewes and goats, due to its high protein content and moderate level of phenolic compounds, mainly consisting of condensed tannins (CT). Preliminary investigations showed analogous positive effects using pelleted and dehydrated sulla forage (DSF) in the diet of dairy ewes, whereas the same effects did not emerge when sulla forage is provided as hay. Thus, dehydration can represent a valid alternative to haymaking for reducing the losses of biomass and nutrients and preserving the properties of bioactive components. The investigations that are the subject of this PhD thesis were aimed to explore the potential of sulla in relation to its seasonal utilization, as fresh or stored forage, and to improve the quality traits of sulla forage stocks, proposing dehydration as alternative to haymaking. Two experiments were carried out in different seasons, spring (SPR) and autumn (AUT), both involving Valle del Belice ewes fed different diets evaluated in terms of feed utilization efficiency, ewes’oxidative status and dairy production. In the SPR experiment, diets consisting of fresh sulla forage (SULLA) or fresh barley forage (BARLEY) provided ad libitum were compared using 12 ewes at 70 days in milk divided into 2 groups and fed the 2 diets in a 2 × 2 Latin square design. In the AUT experiment, pellets of DSF obtained from an early (April) or a late (May) cutting time and differing in crude protein (CP) (April, 15.1% dry matter (DM); May, 11.3% DM) were compared with sulla hay (SH, CP 11.8% DM) using 9 ewes at 60 days in milk divided into 3 groups and fed the following 3 diets in a 3 × 3 Latin square design: A-DSF, 2 kg/day per ewe of April pellets and SH ad libitum; M-DSF, 2 kg/day of May pellets and SH ad libitum; SHL, SH ad libitum. Concentrate feed was supplied to all ewes (600 or 800 g/day in SPR and AUT, respectively). In both experiments, cheeses manufactured from bulk milk of the different groups were sampled at 15 and 30 days of storage. Statistical analyses were performed in SAS 9.2 software using MIXED models for individual ewes’ parameters and GLM procedures for bulk milk and cheese parameters. In SPR, compared to BARLEY, SULLA improved milk yield (1777 vs 1317 g/day; P<0.0001), milk casein (4.00 vs 3.82%; P=0.0020), efficiency of feed conversion in milk (DM intake/milk yield, 1.39 vs 1.85; P<0.0001), and the ewes’ antioxidant balance, while in cheese increased the polyunsaturated fatty acids (PUFA), and reduced redness index (a*) and fat content. In AUT, both DSF diets increased feed intake (3591, 3596, 2963 g DM/day with A-DSF, M-DSF and SHL; P<0.0001) and improved DM digestibility (75.3, 69.6, 67.4% with A-DSF, M-DSF and SHL, P<0.0001) and milk yield in comparison with SH (1667, 1557, 1308 g/day with A-DSF, M- DSF and SHL; P<0.0001), without reducing milk casein. Due to higher intake, estimated daily methane emissions increased with DSF diets (45.4, 45.2, 39.2 g CH4/day with A-DSF, M-DSF and SHL; P<0.0001), while was lower with only A-DSF if referred to milk yield (28.3, 29.9, 31.1 g CH4/kg milk with A-DSF, M-DSF and SHL, P<0.0081). Moreover, feeding A-DSF induced a higher plasma free polyphenols level (13.4, 13.0, 11.5 μg GAE/mL with A-DSF, M-DSF and SHL; P<0.0429) although this was unable to improve the ewes’ oxidative status. In cheese, DSF diets enhanced total PUFA, especially due to linoleic and α-linolenic acids, but only A-DSF diet tended to improve the cheese antioxidant capacity, regardless of storage time.The microbiological profile of SPR and AUT cheeses was almost similar among diets, indicating no negative effect of stored forages on fermentation process. In triangle tests, the panel was able to distinguish cheese from different diets for both seasons and storage times, without recording differences in their acceptance degree. These results confirm the potential of sulla forage as fresh or dehydrated feeding source in the diet for small ruminants, and evidence how dehydration, especially when applied to an early-cut forage, can represent a valid alternative to traditional haymaking, ensuring adequate dairy productions during periods when fresh forage is not available.