Comparison of milk fatty acid profiles of dairy cows grazing cool-season perennial ryegrass or birdsfoot trefoil pasture on a commercial organic dairy farm
This experiment investigated milk fatty acid (FA) profiles of grazing dairy cows on a commercial organic dairy farm during 2 grazing seasons in 2012 and 2013. Eighteen multiparous cows in mid-lactation were assigned to one of 2 intensively rotated grazing treatments in a completely randomized design: cool-season perennial ryegrass (RGP) vs. birdsfoot trefoil pasture (BFTP). Cows received 2.27 kg of concentrate (flaked barley grain and vitamin and mineral supplement) twice per day following milking. Experiment lasted a total of 10 wk, with 2 wk for adjustment to pasture treatments and 8 wk for data and sample collection. Samples of pasture forages and milk were taken at wk 2 and 6 and were analyzed to determine their FA profiles. In 2012 and 2013, averaged concentration of C18:3 n-3 (42.6 and 53.5 g/100 g) was the greatest in pasture forage FA followed by C16:0 (20.5 and 15.7 g/100 g) and C18:2 n-6 (13.9 and 13.5 g/100 g), respectively. The most noticeable difference of pasture forage FA profiles in 2012 and 2013 was that in 2012 proportion of C18:3 n-3 in RGP increased from wk 2 (39.8 g/100 g) to wk 6 (47.1 g/100 g), whereas its proportion in BFTP was similar at wk 2 and wk 6. In contrast, proportion of C18:3 n-3 in RGP and BFTP decreased from wk 2 (57.3 and 55.1 g/100 g) to wk 6 (51.9 and 49.6 g/100 g), respectively. Concentration of trans-11 C18:1 in milk was very low in RGP and BFTP in both grazing seasons, suggesting limited impacts of pasture on the biohydrogenation activity for the pastures tested. Dairy cows grazed on RGP and BFTP showed similar concentrations of cis-9, trans-11 conjugated linoleic acid in milk fat throughout grazing seasons. Cows grazed with BFTP increased concentration of C22:6 (n-3; docosahexaenoic acid) at wk 6 in 2012 and 2013 compared to those grazed with RGP. However, pasture treatment did not affect ratio between polyunsaturated FA and saturated FA in 2 grazing seasons. Overall results in this experiment indicate that source of pastures did not affect major milk FA profiles, and some minor changes in FA profiles may have resulted from pasture FA profiles in 2 grazing seasons.
birdsfoot trefoil pasture, lactating dairy cows, milk fatty acids