Sources of protein and protected methionine on in situ ruminal degradability of crude protein of feed ingredients

Abstract Text: The objective of this study was to evaluate crude protein degradability of feed ingredients in diets containing corn gluten or starea as protein sources, with or without 2g/d protected methionine. Eight male ruminally-cannulated sheep (12 months old, 51.3 kg BW) were assigned to a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments (2 sources of protein - corn gluten or starea - and with or without protected methionine). The in situ nylon bag technique was used in this trial. Samples of feed ingredients were ground to 5mm (corn silage), and 2mm (extruded corn and soybean hulls), and incubated for: 6, 12, 24, 48, 72, and 96 h for corn silage, and 1, 6, 12, 24, and 48 h for extruded corn and soybean hulls. Data were fitted to exponential model to estimate degradation parameters, and effective degradability was calculated with passage rates of 2, 5, and 8%/h. Data were analyzed as a replicated 4 × 4 Latin square with PROC MIXED of SAS. There was no interaction of protein sources and protected methionine, thus only the main effects were studied. Variations from 23 to 91% (corn gluten, and starea, respectively) on protein degradability of protein sources do not affect degradability parameters, potential degradability, and effective degradabilities (2, 5, and 8%/h passage rates) of corn silage and soybean hulls. The average potential degradabilities of crude protein observed were 75.9% (corn silage), and 73.6% (soybean hulls). The average effective degradabilities of crude protein for 3, 5, and 8%/h passage rates were respectively 71.6, 68.8, and 67.7% (corn silage), and 66.1, 58.0, and 53.1% (soybean hulls). The addition of protected methionine improves in 4% the potential crude protein degradability and in 2.8, 2.1, and 1.5% the effective degradabilities of corn silage, for 2, 5, and 8%/h passage rates, respectively. It was concluded that regarding fibrous ingredients, the variation of 68 percentage units in crude protein degradability of protein sources is not enough to modify the ruminal utilization of crude protein of these ingredients. Furthermore, the protected methionine inclusion improves crude protein degradation parameters for low protein ingredients.

Keywords: degradability, methionine, protein sources