Effects of polyphenol, tannin and sucrose addition on milk yield and fatty acid content, and proteolysis, fatty acid composition and fermentation of ensiled alfalfa

This study aims to establish relationships between silage quality and fat content and composition, as well as the post-silage stability of polyunsaturated fatty acid (PUFA) and aerobic stability in alfalfa silage with different additives. The primary objective of the study is to determine the effects of tea phenol extract (TP, containing 50% polyphenols), oak tannin extract (OT, containing 63% condensed tannins), and sucrose (S)addition on lipolysis and proteolysis during the ensiling of alfalfa with high PUFA content. The secondary objective is to investigate the feeding value and milk fatty acid composition of prepared supplemented and non-supplemented alfalfa silages in mid-lactation dairy cows (70-140 days). In this study, four different silage groups were formed: control (C, without additive), TP (4 g/kg DM), OT (15 g/kg DM), and S (10 g/kg DM), and subjected to fermentation for 70 days. Seven multiparous Simmental dairy cows in mid-lactation were randomly assigned to one of four treatment sequences in a switch-back (cross-over factorial arrangement) experimental design. Each experimental period lasted 21 days, consisting of 7 days of ration adaptation and 14 days of data collection. The crude protein (CP) content in silages supplemented with TP and OT extracts were determined as 13.09% and 12.95%, respectively, showing an increase compared to control and S-supplemented silages (P<0.05). Protein loss was significantly lower in all additive-supplemented silages compared to the control (P<0.05). The water-soluble carbohydrate (WSC) content in S-supplemented silages was notably higher than in other silages (P<0.05). Regarding silage fermentation quality criteria, TP and OT supplementation reduced the ammonia-N (NH3-N) content in total nitrogen (P<0.05). Lactic acid (LA) content in all additive-supplemented silage ranged between 74.14 and 94.87 g/kg DM, being higher than in the control silage, while butyric acid concentrations were lower (P<0.05). Polyphenol oxidase (PPO) activity in the control silage (0.77 U/g DM) was lower compared to OT- and S-supplemented silages (P<0.05). Fresh alfalfa showed the highest concentrations of C18:1, C18:3 n-3, C20:5 n-3, ΣPUFA, and Σn-3 fatty acids, but ensiling reduced these concentrations (P<0.05). However, TP supplementation inhibited lipolysis, resulting in higher concentrations of these fatty acids compared to other additives (P < 0.05). Supplementation with TP extract increased dry matter intake and milk yield, demonstrating statistical superiority among silage additives (P<0.05). The cis-9, trans-11 conjugated linoleic acid (CLA) isomer content in milk increased by 22.12% compared to the control silage (P <0.05). OT supplementation increased milk C18:1 cis-9 fatty acid concentration while reducing the n-6/n-3 ratio and the Atherogenic Index (AI) (P<0.05). In conclusion, natural additives such as oak tannins and tea polyphenols have the potential to improve both silage fermentation quality and milk production, as well as milk fatty acid composition. Their ability to enhance CLA content and enrich unsaturated fatty acids suggests their applicability in functional milk production.