Materials and Methods
Milk from bulk tanks was sampled from 11 Ohio herds during May 2000. The milk was analyzed for fatty acids using a gas chromatograph and modifications of the procedure described by Sukhija and Palmquist (1988). The characteristics of the herds, milk yield, and feeding practices were provided via a survey to the farmers. The milk composition data were from the Dairy Herd Improvement laboratory (DHI Cooperative, Inc., Columbus, OH). Characteristics of the herds are provided in Table 1. All, except one or two herds, were fed organically certified feeds. Three of the herds were fed some stored forages at the time of the milk sampling, ranging from 5 to 25 lb/day (as-fed) of corn silage with one of these herds also feeding hay free choice. Grain was fed primarily twice daily, with one herd feeding once and another herd feeding grain three times daily.
| Item | Mean | Range |
| Number of cows | 43 | 12 to 110 |
| Breed, % of cows for all farms | ||
| Ayrshire | 3.6 | 12 to 110 |
| Brown Swiss | 1.8 | 12 to 110 |
| Guernsey | 0.5 | 12 to 110 |
| Holstein | 45.9 | 12 to 110 |
| Jersey | 23.2 | 12 to 110 |
| Mixed | 25.0 | 12 to 110 |
| Milk, lb/day | 50.3 | 4 to 82 |
| Milk fat, % | 3.44 | 2.70 to 4.00 |
| Milk true protein, % | 2.98 | 2.80 to 3.20 |
| Milk urea nitrogen, mg/dl | 12.9 | 10.0 to 17.5 |
| SCC, (cells/ml) x 1000 | 388 | 161 to 931 |
| Days on pasture at data collection | 53 | 35 to 70 |
| Type of pasture | ||
| Grass, % | 66 | 35 to 70 |
| Legume, % | 34 | 35 to 70 |
| Grain DM fed, lb/day2 | 9.8 | 0 to 23.4 |
|
1One herd fed 5.0 lb/day (as-fed) of corn silage and
free choice hay and two herds fed 15 to 25 lb/day (as-fed) of
corn silage.
2Assumed concentrates were 90% DM. |
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