Test Method for Fat Content in Feed

Test Method for Fat Content in Feed

Feed refers to industrially processed products for animal consumption, which are digestible by livestock and poultry, non-toxic to their organisms, and provide essential nutrients, promote growth and development, maintain health, and improve the quality of animal products.

Such products include not only single feed ingredients but also compound feeds formulated with scientific ratios of various raw materials, such as compound feed, concentrated feed, and additive premix feed. According to different purposes and compositions, feed can meet the nutritional needs of various animal species, growth stages, and production objectives.

Experimental Objectives

1.Evaluate Nutritional Value and Energy SupplyFat is one of the most efficient energy sources in feed, providing approximately 2.25 times more energy per unit mass than carbohydrates or proteins. By determining the crude fat content, the metabolizable energy level of feed can be accurately calculated to judge whether it meets the energy requirements of different animals (such as livestock, poultry, aquatic animals, and pets) at specific growth stages.

2.Optimize Feed Formulation DesignDifferent animals have varying fat requirements. For instance, young animals need high levels of essential fatty acids to support nervous system development, while high-yield dairy cows require moderate fat to enhance energy for milk production. Testing fat content facilitates the scientific proportioning of raw materials (e.g., soybean oil, fish meal, extruded soybeans), avoiding indigestion caused by excessive fat or energy deficiency due to insufficient fat, achieving precise nutrient supply.

3.Ensure Feed Quality and FreshnessFat is prone to oxidative deterioration and rancidity, impairing palatability and animal health. By detecting crude fat content combined with indicators such as acid value, peroxide value, and free fatty acids, the freshness and storage stability of fat can be evaluated, preventing the use of inferior raw materials and extending product shelf life.

4.Support Quality Control and Standardized ProductionRegular testing of fat content is a critical part of quality control during feed processing. It monitors batch fluctuations of raw materials, mixing uniformity, and processing losses, ensuring each batch complies with enterprise standards or national specifications (e.g., GB/T 6433), improving product consistency and market competitiveness.

5.Meet Scientific Research and Regulatory RequirementsFat content is fundamental data required for agricultural research, new feed development, and new product registration. Meanwhile, specific products such as infant formula food and pet food must comply with mandatory national standards for fat content (e.g., GB 10765-2021), and testing is a prerequisite for compliance.

Experimental Samples and Instruments

Experimental Sample: Feed

Experimental Instrument: ST-06D Fat Analyzer, compliant with GB 6433

Experimental Procedures

1. Sample Preparation

Take a representative feed sample and grind it to pass completely through a 40-mesh sieve (0.45 mm) to ensure uniformity and extraction efficiency.

For extruded pelleted feed, pre-extraction is required: soak in petroleum and dry to eliminate interference from surface grease before formal testing.

High-moisture samples (e.g., silage) should be pre-dried to constant weight at 60℃±5℃ to prevent fat oxidation.

Weigh 2.0000 g to 5.0000 g of the sample (accurate to 0.0001 g), place it into a constant-weight filter cartridge, and seal for later use.

2. Instrument and Reagent Preparation

Use a Soxhlet extractor (250 mL or 500 mL). Clean the receiving flask, dry it in an oven at 105±2℃ for 1 hour, weigh it after cooling (recorded as m0​).

Anhydrous diethyl  or petroleum  (boiling range 30-60℃) is selected as the solvent, with purity ≥99.5% and peroxide content ≤0.005% to avoid potential safety hazards.

The electronic balance used has a precision of no less than 0.1 mg and is calibrated at least twice a year.

3. Extraction Process

Place the filter cartridge into the extraction tube, add 150-200 mL of solvent to the receiving flask, and assemble the device.

Perform reflux extraction on a constant-temperature water bath at 60-80℃, controlling the reflux rate to 8-10 cycles per hour (updated from the old version), with a total duration of about 6-8 hours until the extract is colorless or no oil stains remain on the filter paper.

For the filter bag method, encapsulate the sample in a special filter bag and place it directly into an automatic extractor, simplifying operations for batch testing.

4.Solvent Recovery and Weighing

After extraction, recover most of the solvent by distillation, and let the remaining small amount volatilize naturally in a fume hood.

Dry the receiving flask in an oven at 105±2℃ for 1 hour, weigh it after cooling in a desiccator (recorded as m1​), and repeat drying until constant weight (difference between two weighings < 0.0008 g).

Experimental Results

The crude fat content of this feed sample is 6.7%, in strict accordance with the requirements of GB/T 6433-2025.