Results and Discussion
Measuring DM intake from pasture is not simple, so grain intake was used to inversely relate to forage consumption. The general trend for the Ohio herds was for CLA concentration in milk to decrease as grain consumption increased (Figure 1), although there were a few outliers. Thus, CLA concentration would have increased with the expected increased DM intake from pasture. Data from other studies were used as reference points to the data from our field study. Dhiman et al. (1999) used treatments of 33:67, 67:33, and 100:0 ratio of pasture to grain intake in Experiment 2. The CLA concentration in milk increased with increasing pasture intake. The CLA concentration was observed for the control diet (TMR with 50% forage, 55:45 alfalfa silage:corn silage) in Experiment 1, the control diet (TMR with 55% alfalfa silage and 45% grain) in Experiment 3, and for Experiment 4, two treatments consisted of 45% forage (50:50 alfalfa hay:corn silage; differing in particle size for alfalfa hay and high moisture ear corn), a treatment with 66% coarsely chopped grass hay, and a treatment with 98.2% coarsely chopped grass hay (Dhiman et al., 1999). The grass hay was made from similar pasture to that used for grazing of cows in Experiment 2. The concentration of the CLA was relatively low for these treatments in Experiments 1, 3, and 4, even though the grass forage was similar to the pasture in Experiment 2 except that it was stored. The data from Kelly et al. (1998) were from cows fed a TMR with 47% forage (51:49 corn silage:legume) or 100% pasture. Concentration of CLA was higher with the cows fed all pasture. The overall trend was for increased concentration of CLA in milk with decreasing amount of grain fed (or increasing amounts of pasture consumed). All data points with CLA concentration in excess of 1.0% of fatty acids in milk represented cows that were consuming pasture.
Figure 1. Comparison of the amount of grain fed (DM) to cows
on pasture and the concentration of conjugated linoleic acid (CLA) in
milk fatty acids (FA). Data were taken from OSU field study (
),
Dhiman et al., 1999 (Experiment 2, 
), Dhiman et al., 1999
(Experiments 1, 3, and 4, 
), and Kelly et al., 1998 (5).