041104 Field Study Shows Pasture Produces Healthier Beef, Milk

Ames, IO - Pastured cattle produce more healthful beef and milk than those finished on preserved forages, according to recent field research at Iowa State University.

Researchers there documented concentrations of conjugated linoleic acid (CLA) in meat and milk from farms in northeast Iowa and southwest Wisconsin (four beef operations and 12 dairies). Farms were visited monthly, the cattle's diet recorded and milk samples taken. Beef was sampled when finished cattle were slaughtered.

Intensively pastured cows produced milk with CLA concentrations that were about 3 to 4-fold greater than the initial concentration. Ribeye steaks from cattle finished on a combination of pasture and concentrates were higher in CLA than steaks from cattle finished on stored forages plus concentrates. Therefore, the researchers concluded that pasture grazing is "an effective method to improve the healthfulness of milk and beef."

The Iowa researchers say the normal concentrations of CLA are about 0.30% of total fatty acids in milk fat and about 0.35% in beef fat. However, these concentrations can be elevated markedly by increasing the supply of precursors of CLA synthesis through nutritional manipulations. For instance, adding plant oils, raw or extruded oil seeds in the diet also increase CLA content in milk. So does grazing.

CLA is a fatty acid thought to help prevent cancer, diabetes and obesity. Beef and milk are two of the main sources of CLA in the human diet. CLA is measured as a percent of total fatty acids found in beef or milk.

Of the four beef producers, one relied on some pasturing of his cattle, while the other three fed only conserved forages. Cattle that were grazed had from 0.34 to 0.46% CLA, while those fed stored feeds had from 0.23 to 0.33% CLA.

One of the beef farms had three groups of cattle. One group was fed alfalfa silage and hay and high moisture corn for the five months of winter and then pastured the following summer. CLA was 0.42%. A second group were started on alfalfa silage and hay and high moisture corn for the five months of winter followed by pasture grazing during the summer and then finally fed alfalfa hay, corn and barley for three months the following winter. CLA percent was 0.46. The third group was pastured in the summer and finished with alfalfa hay, corn and barley during the winter. CLA percent was 0.34.

Cattle from the other three producers were finished entirely on conserved forages, with each farm supplementing different concentrate mixes.

The total lipid contents of ribeye steaks from the first farm that pastured were lower than those of the other three farms. Ribeyes from pastured cattle had total lipid percents of 4.74, 3.82 and 4.62, respectively, according to the feeding procedures described above. The more traditional ways of finishing beef turned in total lipid percents of 8.22, 6.63 and 7.07.

"Feeding system during the finishing period of cattle also seemed to have an effect on the CLA content of ribeye steaks, although differences between farms were not as pronounced as in the dairy farms. The highest CLA-containing ribeye steaks were from groups one (0.42%) and two (0.46%) cattle from Farm A (that pastured)," the researchers summarized. The lowest were from steaks produced by two of the other stored-feed farms (0.23% and 0.26%).

Among the dairy farms, the average concentrations of CLA over the course of this research were 0.35% of total fatty acids in Iowa and 0.27% in Wisconsin. CLA concentrations fluctuated throughout the year, with the highest concentrations in May and June - prime grazing months. In fact, in June, one operation in Iowa, and another in Wisconsin, had average CLA concentrations in their milk of near 1.3%.

Winter months, when stored forages were used, produced the lowest CLA concentrations. In fact, the intensive graziers took cattle off pasture in August and a couple turned them back on in October, resulting in another peak of CLA concentration on those farms, although it was lower than what was obtained during the summer months.

Among the northeast Iowa dairy producers, one farm produced milk with the highest CLA concentrations - 1 and 1.29% of total fatty acids - in May and June, respectively, which is about a 3 to 4-fold increase from the average initial concentration.

In southwest Wisconsin, the highest CLA containing milk was from three farms, with CLA concentrations of 1.10 and 1.38% on one, and 0.80 and 1% on another, in May and June, respectively. The third farm produced milk with a CLA content of 1.08% of total fatty acids in the month of July.

"This study helps confirm on the farm what has already been found to be true in the laboratory," reports Allen Trenkle, an ag professor at Iowa State University. "I think there's a potential of these products having greater value if they can maintain their identity on the market," he added.

Why does pasture-feeding increase CLA content of beef and milk? Trenkle and his associates say that a likely explanation relates to fatty acid composition of the grasses. Linolenic acid accounts for the greatest proportion of the fatty acids in pasture grasses. This fatty acid can be degraded to vaccenic acid in the rumen. Trans-vaccenic acid is a precursor for CLA synthesis in the udder and in meat.

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