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Influence of Various Fiber Sources and Fractions on Milk Fat Percentage

Department of Animal Science, Cornell University, Ithaca, New York 14850

ABSTRACT

Twenty-one Holstein cows were fed hay, corncobs, beet pulp, or oat hulls as experimental crude fiber sources in a continuous feeding trial (16 weeks). Fat tests were previously depressed with a 20% mixed hay-80% pelleted-concentrate ration. The test rations contained 15% crude fiber (6%, from experimental source) and 14% crude protein. All diets significantly increased fat (2.3 to 3.3) (P < .001) and decreased protein (3.71 to 3.63) and solids-not-fat (8.68 to 8.57) (P < .02) percentages. Treatment differences were not significant. For cows with depressed fat tests, significant correlations were fat test change versus a) change in per cent intake of dietary crude fiber ( + .49) (P < .05) and acid-detergent fiber ( + .72) (P < .01), b) absolute intake of acid-detergent fiber ( + .59) (P < .05) and lignin (-.56) (P < .05), and c) absolute digestible intake of acid-detergent fiber ( + .49) (P < .05).

Acid-detergent fiber is superior to crude fiber when relating dietary fiber fractions to fat percentage. It also represents a better-defined component of feedstuffs and is easier to determine.

A second trial conducted with nonlactating cows, fed the fiber sources at 150% of maintenance, showed little difference in acetic :propionic acid ratio when sampled four hours post-prandial.