EFFECTS OF EXTRUDED FLAXSEED AND CONDENSED TANNINS ON RUMEN FERMENTATION, OMASAL FLOW OF NUTRIENTS, MILK COMPOSITION AND MILK FATTY ACID PROFILE IN DAIRY CATTLE

There is interest in increasing the content of omega-3 (n-3; e.g., linolenic acid [C18:3n3]) fatty acids and conjugated linoleic acid (CLA) in bovine milk, primarily because of their beneficial effects on human health. One strategy to alter bovine milk fatty acid composition is the dietary inclusion of flaxseed, which is a rich source of C18:3 n-3. The aim of this study was to evaluate the effects of extrusion processing of flaxseed and the inclusion of condensed tannins (CT) in a flaxseed supplement on omasal flow of nutrients, ruminal fermentation characteristics, animal performance, and milk fatty acid profiles in dairy cattle. Eight multiparous Holstein cows (712.7 ± 92.3 kg body weight; 116.5 ± 17.5 days-in-milk at the beginning of the study) were assigned to four dietary treatments in a replicated 4 x 4 Latin square design consisting of 28-d periods with 20 d of dietary adaptation. Four cows in one Latin square were ruminally-cannulated to allow ruminal and omasal sampling. Cows were fed either a control diet (CTL) or one of 3 treatment diets that consisted of the daily substitution of 3 kg (DM basis) of the CTL concentrate pellet with 3 kg (DM basis) of either a non-extruded flaxseed and pea product (55% flax¬seed, 36% peas, 8% alfalfa, 1% antioxidant; designated RAW), a extruded flaxseed and pea product (55% flaxseed, 36% peas, 8% alfalfa, 1% anti¬oxidant; designated LPR), or a extruded flaxseed and high-tannin fava bean product (55% flaxseed, 36% high-tannin faba beans, 8% alfalfa, 1% antioxidant; designated LPF). Diets were fed twice daily as total mixed rations. Omasal flow of nutrients was estimated using the omasal sampling technique using iNDF as the single indigestible marker. Dry matter intake was lower (P = 0.01) in cows fed the flaxseed diets (24.0 kg/d) compared to those fed CTL (25.9 kg/d). Milk yield was higher (P = 0.02) in cows fed the LPR diet ( 44.4 kg/d) compared to those fed the RAW diet ( 42.3 kg/d); and tended to be higher (P = 0.07) in cows fed the flaxseed diets compared to those fed the CTL diet. Milk fat yield was unaffected by dietary treatment (P = 0.94), whereas milk protein yield tended (P = 0.10) to increase in cows fed the flaxseed diets compared to those fed the CTL diet. No detrimental effects of dietary treatments on ruminal fermentation and omasal flow of microbial protein were observed. The omasal flow of C18:3 n-3 was higher in cows fed the flaxseed diets compared to those fed the CTL diet (P = 0.04), with the RAW diet (56.9 g/d) having the highest flow of C18: 3n-3 compared to the other diets (LPR = 14.0 g/d; LPF = 14.8 g/d). The omasal flow of total CLA isomers were higher (P = 0.03) in cows fed the LPF diet (6.06 g/d) compared to those fed the LPR diet (3.70 g/d). The C18:3 n-3 content in milk fat (% of fatty acid methyl esters) was higher in cows fed the LPR diet (0.950%) compared to those fed the RAW diet (0.745%). The level of total CLA isomers in milk was also higher in cows fed the LPR diet (0.845%) compared to those fed the RAW diet (0.308%). These results demonstrated that feeding extruded flaxseed products is more effective than feeding whole flaxseed at improving the fatty acid composition of milk fat without negatively impacting animal performance and ruminal fermentation; however, the inclusion of CT in the extruded flaxseed product had no additional benefit