Rumen Volatile Fatty Acids and Milk Composition from Cows Fed Hay, Haylage, or Urea-Treated Corn Silage

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Abstract
Alfalfa-brome hay, haylage, .5% urea-treated corn silage or .5% urea plus 1% dried whey-treated corn silage was fed as the only forage to 1 of 4 groups of 10 lactating cows per group for a lactation trial of 10 wk. Rumen samples were collected via stomach tube 3-4 h after the morning feeding. The pH of the rumen samples from cows fed hay was higher than for cows fed haylage, urea-treated corn silage and urea-whey corn silage: 6.69 vs. 6.36, 6.40 and 6.50. Total volatile fatty acids and propionate were highest from cows fed urea-whey corn silage and were higher on all 3 fermented forages than cows fed hay. Acetate/propionate ratio was highest from cows fed hay and lowest from cows fed corn silages. Butyrate was highest from cows fed haylage or hay. Milk protein composition was not affected by ration although nonprotein N of milk was highest from cows fed the urea-treated corn silages. Oleic acid and total unsaturated fatty acids were lowest in milk fat from cows fed hay, while palmitic acid was highest from cows fed hay and haylage. Type of forage fed may cause small changes in rumen fermentation and in milk composition. The importance of these changes is unknown, but may affect properties of dairy products produced from this milk.