Variation in menhaden fish meal characteristics and their effects on ruminal protein degradation as assessed by various techniques

Menhaden fish meal (FM) samples (n = 17) from five processing plants were used to evaluate effects of preparation on ruminal degradation of FM protein. The ability of routine industry measurements to predict ruminal protein degradation was also assessed. Industry measurements included fish quality (total volatile nitrogen, TVN), soluble addback (SOLADD), pepsin degradability and drying temperature (DRYT). Crude protein (CP) and fat contents of FM samples ranged from 65.0 to 75.4% and 9.1 to 12.7% of dry matter, respectively. Ruminal degradation of FM protein was determined by the in situ bag technique (BAGDEG, range of 27.4 to 56.4%). The ficin enzyme technique provided estimates of ruminal solubility (range of 6.0 to 33.9%) and ruminal degradation (range of 28.6 to 57.0%) of FM protein. Pearson correlation coefficients and probabilities for comparisons of BAGDEG with other estimates of degradability and FM preparation characteristics were determined. Equations to predict BAGDEG from routine industry measurements and from other estimates of degradation were developed. The amount of SOLADD explained 75% of the variation in BAGDEG and up to 81% of the variation was explained by including DRYT and CP. Prediction equations were evaluated using 10 additional menhaden FM samples. Coefficients of determination for comparisons of determined BAGDEG with predicted values from models containing up to 5 independent components ranged from 0.76 to 0.81 (P < 0.001). Results confirm that preparation methods alter ruminal degradation of FM protein. Data demonstrate a one variable model using SOLADD provides a simple, rapid and inexpensive way to predict ruminal degradation (BAGDEG) of menhaden FM protein and suggest measurements of ruminal solubility are the most closely correlated predictors of ruminal degradation for FM protein.