An Evaluation of Methods for Preserving Fresh Forage Samples Before Protein Fraction Determinations

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Abstract
A study was conducted to determine the most desirable method of preserving freshly cut forage samples before determination of various protein fractions. Four types of forages, bromegrass (Bromis inermis), birdsfoot trefoil (Lotus corniculatus) and alfalfa (Medicago sativa) at the vegetative and full-bloom stages of growth, were evaluated for this study. For each forage, a sample composited from three replicated small plots was divided when first cut into seven subsamples. Each was then preserved by one of seven methods: freezing in liquid N immediately or 1 h later, freezing at −23°C 1 or 2 h later in a conventional freezer, drying in a forced-air oven at 55°C for 24 h at 1 or 2 h after cutting or air-drying at room temperature (20°C) for 48 h. Frozen samples subsequently were dried by lyophilization. Observed values averaged 12.9% lower for CP, 20.0% higher for protein solubility, 18.4% lower for protein resistant to protease degradation and 47.5% lower for protein in the NDF fraction when preserved by freezing followed by freeze-drying. Newer diet formulation systems are dependent on the accuracy of these values in predicting microbial yield and diet protein escaping degradation that is available to the animal. Oven drying will result in underestimating protein solubility and overestimating true plant protein escaping ruminal degradation. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science

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