Effects of hay, dehydrated and fresh sulla forage on feed intake, milk production and oxidative status of ewes

Abstract

Take home Message Dehydration is a valid opportunity to exploit the favorable responses of dairy ruminants to sulla forage-based diets also in periods when fresh forage is unavailable. Introduction The choice of sulla (Sulla coronarium L.) was based on the widespread availability of this legume species in Mediterranean areas, where it is recognized for the excellent agronomic traits, and fresh sulla forage (FSF) is appreciated for the positive effects of its high protein content and moderate condensed tannins (CT) concentration on intake, milk yield and milk composition of small ruminants (Bonanno et al., 2016). At moderate level (<6% DM), CT bind dietary protein, protecting it from ruminal degradation and contributing to increase its intestinal absorption and utilization for milk casein synthesis. CT exert also an antioxidant activity which was able to improve the plasma oxidative status of goats (Giorgio et al., 2020). Dehydration of FSF could be a valid process to preserve these properties, as an alternative to hay-making which causes great losses of nutrients and bioactive components. The aim of this research was to evaluate the responses, in terms of feed intake, milk yield and oxidative status, of dairy ewes fed with diet based on sulla hay (SH), pelleted dehydrated sulla forage (DSF), and FSF. Material and methods Ten primiparous (PRI) and ten pluriparous (PLU) Valle del Belice ewes at 60 days in milk were distributed into 5 homogeneous groups, fed 5 diets in a partial 5×2 Latin square design with 5 groups and 2 periods. The diets were different for the forage basis: SHL = SH ad libitum (al); DSF2 = 2 kg/d DSF + SH al; FSF2 = 2 kg/d FSF + SH al; FSF4 = 4 kg/d FSF + SH al; FSFL = FSF al. The diets were integrated with energetic concentrate at level of 800 g/d for PRI or 1,200 g/d for PLU. Ewes’ feed intake and milk yield were recorded daily. Forages and concentrate were sampled to determine centesimal composition, polyphenols, CT and fatty acids. Faeces composition was used to estimate diets digestibility. Milk was analysed for its components and clotting ability, and plasma to determine oxidant (ROMs, reactive oxygen metabolites) and antioxidant substances (BAP, biological antioxidant potential), and the oxidative stress index (OSI = ROMs/BAP). Results and discussion DSF,compared to FSF and contrary to SH, showed a slight reduction of protein, a moderate increase in the fibre content, no loss in terms of vitamin E and polyunsaturated fatty acids, and a decrease in CT and polyphenols due to dehydration treatment. There was higher DM intake with DSF2 diet than with other diets (table 1), indicating the good palatability of DSF. DSF2 diet implied also higher protein and vitamin E intakes than other diets, whereas compared to FSFL its intake was analogous for net energy and lower for CT and polyphenols. DM digestibility was analogous among diets. The antioxidant protection exerted by the higher vitamin E intake can be responsible of the greater oxidative status of ewes fed DSF2 diet, that exhibited lower values of ROM and OSI at plasma level (table 1). Milk yield and casein percentage (table 1) with DSF2 diet were comparable to those with FSF4 and FSFL diets, characterized by higher incidences of green forage, whereas curd firmness (a2r) similarly improved with DSF2 and FSFL diets. This result confirms the positive impact of FSF on milk production, presumably due to the effect of CT on the efficiency of dietary protein utilization for the synthesis of milk casein, and shows that advantageous effects on milk production emerges also when FSF is replaced by DSF. Conclusion The inclusion of 2 kg of DSF in the diet gave better results than a diet exclusively based on sulla hay, and was comparable to diets with higher levels of FSF in terms of milk yield and casein. Since dehydration preserved the vitamin E content, the dehydrated sulla can have contributed to enhanc