Chestnut or quebracho tannins in the diet of grazing ewes supplemented with soybean oil: Effects on animal performances, blood parameters and fatty acid composition of plasma and milk lipids

The aim of the present study was to evaluate the effect of the inclusion of chestnut or quebracho tannin extracts in the diet of grazing ewes supplemented with soybean oil, on the blood plasma and milk fatty acid profile, milk quality traits and animal metabolic profile. Eighteen Comisana ewes at 172 ± 6 days in milking were allotted into 3 experimental groups. Diets were characterized by pasture ad libitum administered and by 800 g/head and day of 3 experimental concentrates containing 84.5 g of soybean oil/kg of DM and 52.8 g/kg DM of bentonite (Control diet) or 52.8 g/kg DM of chestnut tannin extract (hydrolysable tannins, CHE diet) or 52.8 g/kg DM of quebracho tannin extract (condensed tannins, QUE diet). The trial lasted 4 weeks after 15 days of adaptation to the feeding regimen. Milk yield was daily recorded while milk composition and blood parameters were weekly analysed. CHE and QUE did not affect the milk yield and composition. Casein Index was affected by diet and it was significant higher in milk from animals fed QUE (P < 0.0259). The clotting parameters with the exception of a30 were affected by tannins: r was higher for QUE milk while k20 increased regardless the kind of tannin. Blood parameters were not affected by tannins and the oxidative status of ewes, determined using MDA as indicator, did not present significant differences among groups, regardless the concentrates fed to animals. Fatty acid profile of blood plasma demonstrated that tannin extract, regardless the source, favored the accumulation of vaccenic acid (trans-11 18:1) reducing the hematic concentration of stearic acid (18:0). Only few significant differences in milk fatty acid profile were found. In particular, rumenic acid (cis-9, trans-11 18:2) increased when the concentrates contained polyphenols and the stronger effect is reached with QUE (P < 0.0002).