Effect of oak acorn with or without polyethylene glycol in diets containing extruded soybean on milk fatty acid profile, ruminal fermentation and plasma metabolites of lactating goats

Oak (Quercus persica) acorn (OA) contains high levels of hydrolysable tannins that can alter the biohydrogenation (BH) of unsaturated fatty acids (FA) in the rumen. Addition of polyethylene glycol (PEG) to diet containing OA may reduce the inhibitory effect of oak tannins on BH of FA by rumen bacteria. Furthermore, increasing BH intermediates is more pronounced with extruding than other thermal processing of oilseeds. This study assessed the effect of OA with or without PEG in diets containing extruded soybean seed on intake, digestibility, ruminal fermentation, plasma metabolites, and milk production, composition and FA profile of lactating goats. Twenty-one multiparous lactating goats (BW = 42.7 +/- 6.1 kg; DIM = 14 +/- 2) were divided into three groups (7 animals/group) based on BW and milk yield. The animals assigned randomly to one of the three experimental diets-control diet (C; without OA and PEG), and diets containing 100 g/kg DM of OA without PEG (OA - PEG) or with 20 g/day PEG (OA + PEG). All diets contained 150 g/kg DM extruded soybean seed. Goats fed both OA - PEG and OA + PEG diets had greater DMI compared to the C diet (p < 0.01). Milk yield and composition were not affected by experimental diets (p > 0.05), whereas goats fed the OA - PEG diet had higher milk protein, lactose and solid not fat yield (p < 0.01). Digestibility of crude protein was lower in goats fed the OA - PEG diet than other groups (p < 0.01). Experimental diets had no effect on ruminal fluid pH and volatile FA concentrations (p > 0.05), but NH3-N concentration was lower in goats fed the OA - PEG diet than other groups (p < 0.01). Plasma glucose, urea, total protein, total cholesterol, triglyceride and albumin concentrations were not affected by inclusion of OA and PEG to the diet (p > 0.05). Goats fed the OA - PEG diet had higher milk vaccenic acid (trans-11 C18:1) and conjugated linoleic acid (cis-9, trans-11 C18:2) concentrations compared to those fed the C and OA + PEG diets (p < 0.01). In conclusion, the addition of OA (100 g/kg DM) to a diet containing extruded soybean seed not only had no adverse effects on performance, rurninal fermentation and plasma metabolites but also improved the nutritional value of goat's milk fat for human consumption. In addition, inclusion of PEG to diet containing OA decreased the beneficial effect of OA tannins on milk cis-9, trans-11 C18:2 and trans-11 C18:1 concentrations.