Supplementation of by-products from grape, tomato and myrtle affects antioxidant status of dairy ewes and milk fatty acid profile

The aim of this study was to evaluate the effect of diets containing different dried by-products on milk and blood plasma antioxidant capacity of dairy ewes. Thirty-six Sarda ewes were assigned to four treatments: control (CON; no by-product), 100 g/day of grape marc (GM), 100 g/day tomato pomace (TP) and 75 g/day of exhausted myrtle berries (EMBs). The superoxide dismutase (SOD), glutathione reductase (GR), glutathione transferase (GST) and glutathione peroxidase (GSH-Px) in blood, and SOD, GR and lactoperoxidase (LPO) in milk were determined. Total antioxidant capacity (FRAP and ABTS assays), malondialdehyde (MDA) and protein carbonyls (PCs) were also measured. Milk fatty acid profile was investigated by gas chromatography. The results showed higher antioxidant capacity measured by FRAP or ABTS assays and a reduction in MDA in GM plasma than CON. All by-products enhanced the protection of milk proteins by oxidation, as evidenced by lower values of PCs compared with CON. GM supplementation increased PUFAn-6, due to increase in C18:2n-6, the main component of GM compared with CON. All by-products did not modify the nutritional indexes of milk fat. In conclusion, dietary GM may enhance protection against oxidative condition of dairy ewes, whereas TP and EMB need further research to define the optimum inclusion level in sheep diet.