Tannins as feed additives to modulate ruminal biohydrogenation: Effects on animal performance, milk fatty acid composition and ruminal fermentation in dairy ewes fed a diet containing sunflower oil

In vitro studies have suggested that feeding tannins to ruminants can favourably alter ruminal biohydrogenation of dietary linoleic acid, enhancing accumulation of trans-11 18:1 (VA, vaccenic acid) in the rumen and thereby the content of some human health promoting fatty acids, such as VA and cis-9 trans-11 18:2 (rumenic acid, RA), in dairy or meat products. However, reports on impacts of these phenolic compounds on milk fatty acid (FA) profile are very limited and inconsistent. Therefore, fourteen Assaf ewes in mid lactation were used to examine effects of addition of a mixture (1:1, w/w) of two commercial oenological extracts of quebracho condensed tannins (CT) and chestnut hydrolysable tannins (HT) to a diet containing sunflower oil (SO) on animal performance, milk yield and composition, and ruminal fermentation. All sheep received a total mixed ration based on alfalfa hay and a concentrate (400:600), supplemented with 20 g of SO/kg dry matter (DM) plus 0 (Control; n = 7) or 10 (TAN; n = 7) g of tannins/kg DM. Milk production and composition was analyzed on days 0, 3, 6, 9, 12, 15, 18, 21, 24 and 27 on treatments, and milk FA profile on days 0, 3, 6, 12, 18 and 27. Neither DM intake nor milk, or its component, yield was affected by TAN treatment. Similarly, addition of the extract of tannins to a SO containing ration did not alter concentrations of the major FA classes in milk (i.e., saturates, monounsaturates, and polyunsaturates), had very limited effects on the proportion of particular FA, and was not able to enhance milk VA and RA enrichment above that achieved with SO supplementation. Temporal changes in milk FA composition were characterized by an increase in unsaturated FA with 18 carbons, mainly cis and trans 18:1, and a concomitant reduction in most short and medium chain saturates (6:0 to 12:0 and 16:0; P<0.05) attributable to the presence of SO in the diet. Addition of tannins did not affect ruminal fermentation parameters (i.e., pH, lactate, ammonia, and total volatile fatty acid concentrations) measured after 28 days. Reasons for the lack of effects of either type (quebracho CT and chestnut HT) or amount of tannins in the diet are discussed.