Effects of Processing Method on Degradation Characteristics of Protein and Carbohydrate Sources In Situ

Abstract

Two ruminally cannulated Holstein cows in early lactation were used to determine the effects of heat treatment and particle size on fractional degradation rates and ruminal degradabilities of DM, CP, and total nonstructural carbohydrate of dry shelled corn and soybeans. A randomized complete block design with cows as blocks was used. Carbohydrate sources were cracked corn, chick cracked corn, finely ground corn, and steam-flaked corn. Protein sources were soybeans that were roasted at 144°C, cracked, or ground through a 4-mm screen and raw soybeans that were cracked or ground through a 4-mm screen. Reduction in particle size increased both degradability of CP and total nonstructural carbohydrate in the rumen. Heat treatment decreased degradability of CP and increased degradability of total nonstructural carbohydrate in the rumen for both protein and carbohydrate sources. Roasting of soybeans decreased degradability of all AA except Lys. However, reduction in particle size had a stronger effect than heat treatment on ruminal degradability of CP and AA of soybeans, but had the opposite effect on total nonstructural carbohydrate degradability from corn. Methionine, Leu, and Thr had the lowest ruminal degradability across all soybean sources, and Lys and Val were the most degradable. The AA profile of the RUP fraction of soybeans differed from that of the original feedstuff and was affected by processing method.