How To Interpret Your Feed Test – What The Parameters Really Mean?

This article is not intended to be a comprehensive explanation of interpreting your feed test results but aims to provide a ‘snapshot’ of key parameters you should be looking at when understanding the quality of your Hay.

Why Feed Test?

The quality of the diet is predictive of animal performance. Measuring forage quality enables producers to evaluate and optimise the meeting of production targets.

There is large variance in feed composition, even in the same product type (Table 1). If you don’t test your feed, how do you know what you are feeding?

The greatest cost in an animal production system is the feed component. The difference in nutritional composition between “expected average” and true result can lead to a large cost difference.

We want to ensure that we are meeting the animals’ nutritional requirements in a cost-effective way.

Metabolisable Energy (ME)

Energy is an essential requirement for homeostasis, healthy pregnancy, sustained milk production, movement and weight gain.

Commonly, metabolizable energy (ME) is the value evaluated to assess the energy content of feed. ME is calculated by gross feed energy minus the energy lost in the faeces, urine and gases. It is the energy available for use by the animal. The main components contributing

to energy content are carbohydrates, fats and proteins; coupled with the digestibility of the feed source. Generally, the higher the energy content, the higher production capacity of the feed.

Crude Protein (CP)

Protein is necessary for maintenance, growth, lactation and reproduction of the animal. It is the measure of nitrogen in the feed source; including true protein, ammonia, nitrates, amines, amino acids, peptides, and nucleic acid nitrogen.

True protein and non-protein nitrogen are both utilised by the microbes in the rumen to synthesise microbial protein. This microbial protein is the primary source of protein absorbed and utilised by the animal.

Protein and energy must be in balance in order to be most effectively utilised by the animal. Excess of one or the other can lead to inefficiencies of digestion processes and loss.

Carbohydrates

Carbohydrates are the major source of energy in diets. Their main function is to perform as an energy source for both the rumen microbes and the animal.

Neutral Detergent Fibre (NDF) & Acid Detergent Fibre (ADF)

These are the structural carbohydrate component of feed, providing the necessary “skeleton” of the plant. Fibre is directly correlated with the amount of forage an animal can consume, restricting daily intake of nutrients. Digestible fibre provides energy to the animal via microbial processing. Indigestible fibre (largely ADF) passes through faeces.

Neutral Detergent Fibre (NDF) is a measure of the overall fibrous bulk of the forage, including hemicellulose, cellulose, lignin. Generally, the lower the NDF the better the quality, as this allows the animal to rapidly absorb the nutrients of the feed.

Acid Detergent Fibre (ADF) is the least digestible component of the plant, comprising of cellulose, lignin, silca and insoluble nitrogen. Cellulose is variable in digestibility, as lignin content increases, cellulose digestibility decreases.

Relative Feed Value (RFV) & Relative Forage Quality (RFQ)

Relative feed value (RFV) and relative forage quality (RFQ) both use nutritional components to serve as an indicator of forage quality. They both utilise a scoring system where the higher the number, the better the quality. 100 is considered an average result,.

RFV is based solely on ADF and NDF values. RFQ also includes CP, fat, ash and NDF digestibility, providing an enhanced evaluation of forage quality.

Absolute values should not be used for making direct comparisons. Rather a range of values should be used to classify a forage. A good rule of thumb is to accept anything within at least +/- 5 points of the target value.

What Are Good Results?

“Good” results depend upon the product type. For example, a CP of 12% in Cereal Hay is considered excellent, but if 12 %CP was the results of a Legume Hay, we consider this to be quite a poor result.

Here’s a helpful chart to cut out and stick somewhere where you can refer to it easily: