Effects of tannins on the fatty acid profiles of rumen fluids and milk from lactating goats fed a total mixed ration containing rapeseed oil

The 4 experimental diets, all containing rapeseed oil, consisted of one control and 3 other diets supplemented with 3 different levels of commercial oenological extracts tannins (i.e. 3, 6 and 9 g/kg dry matter (DM), respectively). The effect of the added tannins on the fatty acid profiles of ruminal fluid was tested in vitro, and 20 multiparous Liuyang black nannies [average body weight (BW): 26.3 +/- 0.5 kg] at week 6 of lactation were used in an in vivo experiment. For the in vitro experiment, the inclusion of dietary tannins did not (P > 0.05) affect fatty acid contents in the culture fluid in vitro, except the percentage of total conjugated linoleic acid (CLA) tended to increase (quadratically, P = 0.075) with increasing tannins level. Increasing incubation time decreased the percentage of total cis C17:1 (P = 0.001), cis-11 C18:1 (P < 0.0001), cis-12 C18:1 (P < 0.0001), trans-11 C18:1 (P = 0.016), total cis C18:1 (P < 0.0001) and C18:1 (P < 0.0001), cis-9, cis-12 C18:2 n-6 linoleic acid (LA) (P < 0.0001) and total n-6 polyunsaturated fatty acids (PUFA) (P = 0.001). In the in vivo experiment, concentration of C16:1 in goat milk linearly increased (P = 0.032) and that of cis-11 C18:1 tended (quadratic effect, P = 0.072) to increase with increasing levels of tannins. Tannin inclusion did not affect (P > 0.05) the content of protein, lactose, ash, solid not fat and total solids in the goat milk, but higher levels of tannins reduced milk fat content (P = 0.005), compared with the control diet. Compared with the control, tannins inclusion decreased concentrations of cis-11 C20:1 (P = 0.022) and total n-9 monounsaturated fatty acids (MUFA) (P = 0.017) in milk at the 3 g/kg DM inclusion rate, decreased C11:0 (P = 0.012) and C13:0 (P = 0.029) at 6 g/kg DM, but increased cis-9 C18:1 (P = 0.043) and C22:6 n-3 docosahexenoic acid (DHA) (P = 0.013) at the 9 g/kg DM inclusion rate. Concentrations of cis-14 C18:1, cis-9, cis-12 C18:2 n-6 LA, total cis MUFA, PUFA, n-3 and n-6 PUFA in milk linearly increased (P < 0.05) with increasing dietary tannins. These data indicate that dietary inclusion of rapeseed oil in combination with tannins would be an effective tool for increasing the unsaturated fatty acids content in goat milk.