Predicting the Effect of Proteolysis on Ruminal Crude Protein Degradation of Legume and Grass Silages Using Near-Infrared Reflectance Spectroscopy

¹ Department of Dairy Science, University of Wisconsin, Madison 53706
² Department of Soil Science, University of Wisconsin, Madison 53706
³ Department of Agronomy, University of Wisconsin, Madison 53706

Two studies were conducted to assess whether routine applications of near infrared reflectance spectroscopy could predict the effects of silage proteolysis on ruminal crude protein (CP) degradation of legume and grass silages. A preliminary study was conducted to assess the effect of laboratory drying method on ruminal CP degradation of silages. Thirty legume and grass silages were freeze-, oven-, or microwave-dried and incubated in situ in the ventral rumen of three ruminally cannulated cows for 24 h. Freeze-drying was considered least likely to alter ruminal CP degradation of the silages; therefore, oven- and microwave-drying were compared using first-order regression with freeze-drying. Oven-drying for 48 h at 55°C compared favorably (R² = 0.84) with freeze-drying. Microwave-drying resulted in a large bias (2.84 g/10^–1 kg of CP) and was poorly related (R² = 0.48) to freeze-drying.

In a second study, alfalfa and timothy were cut at three maturities and allowed to wilt for 0, 10, 24, 32, 48, and 54 h. Forages were ensiled in triplicate cylindrical mini silos and allowed to ferment for 120 d. After fermentation, silages were oven-dried, ground, and scanned on a near-infrared reflectance spectrophotometer. Duplicate, dried, 2-mm ground silage samples were incubated in the ventral rumen of three ruminally cannulated cows for 24 h. Forage species, maturity, and wilting time significantly affected 24-h ruminal CP degradation of the silages. Near-infrared reflectance spectroscopy accurately predicted (R² = 0.91) 24-h ruminal CP degradation of silages. Data suggest near-infrared reflectance spectroscopy can accurately assess the effects of forage species, maturity, and wilting time (proteolysis) on 24-h ruminal CP degradation of legume and grass silages.

Key Words: silage • proteolysis • near infrared • in situ

Submitted on July 13, 1998
Accepted on November 23, 1998

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