Effect of pasture botanical composition on milk quality in organic production

Summary

A continuous grazing experiment with three measurement periods, 3 weeks each, was conducted with 16 Norwegian Red dairy cows in mid lactation to compare milk quality when grazing red clover-grass (R) or botanical diverse pasture (D). The cows were offered either R or D from the start of grazing season in mid May until beginning of September 2008. Milk yield was measured and milk samples were collected in the last week in each period (end of June, beginning of August and end of August). Pasture type had no effect on milk yield and milk content of fat or protein. Cows grazing R had higher proportion of the fatty acids C18:0 (22.41 vs. 9.96, P<0.05) and C18:1t11 (0.58 vs. 0.44 g/100g FAME, P<0.05) and lower proportion of C16:0 (27.83 vs. 30.92, P<0.05) in their milk fat than the cows grazing D. The milk content of ?-tocopherol was higher in milk from R than D (3.01 vs. 2.64 µg/ml, P<0.05). The oxidative stability of the milk lipids were only minor affected by pasture type.