Milk production, composition, and milk fatty acid profile from grazing sheep fed diets supplemented with chestnut tannin extract and extruded linseed

Tannins are bioactive compounds able to interfere with protein and lipid metabolism in the rumen, by forming undegradable complexes with dietary proteins and by modulating several bacterial activities, including the biohydrogenation of polyunsaturated fatty acids. The aim of this trial was to study the effect of dietary supplementation with chestnut hydrolysable tannin extract on ewes milk yield and quality. Ninety-six multiparous Sarda ewes in their mid-lactation phase were allotted to two homogeneous groups (control group, C group; group fed concentrate supplemented with chestnut tannin extract, CHE group), each of 48 animals, for a feeding trial. Animals of both groups grazed 8. h per day on the same pasture based on a mixture of Lolium multiflorum, Avena sativa and Trifolium repens (1:1:1). The two diets differed only in their concentrate supplement. The control group received 450. g/head per day of a concentrate feed without chestnut tannin extract, whereas the CHE group received 500. g/head per day of a concentrate feed formulated with the same ingredients of the control concentrate plus 80.0. g/kg DM of chestnut tannin extract. The amounts of concentrate offered to the animals of both groups were calculated in order to obtain isoproteic and isoenergetic dietary treatments considering the expected DM intake of animals. The inclusion of chestnut tannin in the concentrate resulted in a greater production of milk (+18.64%; P <. 0.001). Moreover, no differences in casein fraction profile between milks from both groups were found while the casein index was greater (P = 0.034) in milk from ewes fed CHE than milk from ewes fed C. As regard fatty acid composition, milk from CHE group had a greater concentration of omega-3 fatty acids if compared to milk from C group (alpha-linolenic acid: 2.18 vs 2.57. g/100. g of total lipids in C and CHE group, respectively), whereas the percentage of CLA and of C18:1 trans11 in milk fat from CHE group was smaller (CLA: 2.20 vs 1.85. g/100. g of total lipids, in C and CHE group, respectively with P = 0.001; C18:1 trans11: 3.89 vs 3.57. g/100. g of total lipids in C and CHE group, respectively with P = 0.001). The use of practical doses of CHT in the diet of grazing ewes may improve the response to dietary linseed supplementation, resulting in milk with a greater concentration of alpha-linolenic acid.