Total phenols, total and condensed tannin contents and their relationship with nutritive value of alpine pastures

Two investigations were carried out in the Northwest Italy (Susa and Chisone Valleys). The pastures were natural grasslands without any kind of fertilization and were located in five sites at an altitude range of 1704-2070 m a.s.l. during the first trial in the 2013 grazing season and in nine sites at an altitude range of 1620-2070 m a.s.l. during the second trial in the 2014 grazing season. Collected samples were analysed for total phenol (TP), total tannin (TT) and condensed tannin (CT) contents and results were correlated to chemical composition and in vitro digestibility reported in previous papers. A significant correlation between all the tannin fractions was found regarding the acid detergent lignin (ADL) pasture contents. A higher correlation (P<0.01) was found for TP and TT fractions (0.747 and 0.717, respectively), while CT fraction showed a lower one (0.436, P<0.05). Principal component analysis confirmed that as far as tannins fractions are concerned, TP and TT were closely associated with ADL as shown in the distribution of the variables (positive quadrant of the right part), while CT fraction was less correlated. The results highlight the importance of the tannins quantity and quality of the pasture, that can, due to the changes in the nutritional composition of pastures, affect milk quality during the grazing season.