Milk fatty acid composition of dairy cows fed green whole-plant buckwheat, phacelia or chicory in their vegetative and reproductive stage

The hypothesis was tested that the phenological stage of dicotyledonous forages influences milk fatty acid (FA) composition of dairy cows. For this purpose buckwheat (Fagopyrum esculentum) and phacelia (Phacelia tanacetifolia; both in their first year of cultivation) as well as chicory (Cychorium intybus; second year) were cultivated in mixture with ryegrass (Lolium multiflorum). After 35 days of growth, feeding the green forages to 3 × 6 late lactating dairy cows at ad libitum access started. The realized dietary dry matter proportions of the test plants were (vegetative and reproductive stage): buckwheat, 0.60 and 0.55; chicory, 0.70 and 0.69; phacelia, 0.51 and 0.48. Experimental feeding lasted for 23, 17 and 26 days with buckwheat, chicory and phacelia, respectively. The complete diets additionally contained 2 kg of concentrate and 1 kg of barley straw per day per animal. Milk and feed samples were analyzed from every second day. Feedstuffs were analyzed for proximate contents, FA and fractions of phenolic compounds. In milk samples solids and FA were measured. Contents of FA and of phenol fractions decreased during advancing development stage in all test plants except total extractable phenols and total tannins in phacelia. This decrease was particularly pronounced for α-linolenic acid (ALA) and linoleic acid (LA) in buckwheat. Phenological stage had no influence on milk yield and gross composition, but ALA and LA proportions of milk fat declined with time in all groups. Proportions of ALA (14.2 g/kg FA) and total poly-unsaturated FA in milk fat were highest with phacelia. Levels of conjugated linoleic acid (CLA) in milk fat were not affected by treatment or phenological stage. Vaccenic acid in milk fat was slightly elevated when feeding buckwheat and phacelia in the reproductive stage whereas it decreased with ongoing development in the chicory group. No systematic influence of phenological stage on the relative recovery of feed FA in milk fat occurred. The study did not confirm the hypothesis that the recovery rate of ALA would increase with maturing of the forages. In terms of generating a desired milk FA profile, phacelia and chicory seem however to be generally promising.