Biological assays in animal production are analytical methods used to estimate the potency of substances or agents by observing their effects on living animals (in vivo) or tissues (in vitro).
Protein Efficiency Ratio (PER) and Its Role in Animal Nutrition
Protein efficiency ratio, which is a measure of protein quality, is defined as the ratio of grams of protein consumed. In other words, it is based on the weight of the test subject divided by its intake of a particular food protein during a test period.
PER = Gain in body mass (g) / Protein intake (g)
PER has been the most widely used measure of protein quality, particularly because of its simplicity.
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Net Protein Utilization (NPU) in Animal Feed Evaluation
The net protein utilization of a food is the percentage of protein contained in that food that is retained by the body after the food has been eaten. Hence, it is used to describe the value or usefulness of certain proteins in a diet.
A simple equation for NPU is:
NPU = (Nitrogen Retained × 100) / Nitrogen Intake
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Biological Value (BV) as a Measure of Protein Retention
Biological value of a food is the percentage of absorbed protein from the food that is retained in the body and available for incorporation into the proteins in the body of the organism that consumed it.
It is a useful value when on a diet, for example, for weight loss or muscle gain. Proteins are the major source of dietary nitrogen. The equation for BV is:
BV = (Nitrogen Retained (Nr) × 100) / Nitrogen Absorbed (Na)
For accurate determination of BV, the test organism must only consume protein from the test diet. The test protein must contain no known sources of non-protein nitrogen, such as urea, and the test diet must be of good quality to prevent the protein in the diet from being used as the primary energy source.
Typically, a BV test can last for over one week. Fasting prior to testing helps produce consistency between subjects.
The use of biological assay techniques in animal production has proven vital in the assessment of the potency of proteins in feedstuffs.
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