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Understanding laboratory results
Understanding laboratory analysis is crucial to provide a balanced diet and establish proper feeding practices. In previous articles, we explained the importance of testing the feed to comprehend the nutrient requirements of animals. Knowing how to interpret laboratory results is indeed vital to understand feed nutritional analyses. To enable interested farmers to understand lab analyses results, basic guidelines are given below. Further explanations, as well as guidelines on how to work out a ration, will be given in following articles.
How to interpret laboratory analysis?
When we face lab results they usually look like the table presented below (Table 1). However, not all the laboratories perform the same analyses. There are different ways of analysing the same component. Crude fibre was the common way to measure the fibre content of the feed, whereas, nowadays, it is preferred to measure it by Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF) and Lignin since this is a more accurate way of analysing the fibre. In the same way crude protein, the traditional way of measuring the protein content, now it is being substituted by true protein. Crude protein is less accurate and tends to overestimate the protein content.
We will focus on how to interpret lab results according to the needs of a dry beef cow (non-pregnant) in the tropics. However, you need to consider that there are differences between breeds and even between individuals of the same breed. The following requirements are just general values that should be carefully adjusted to the needs of every farm and production condition.
Laboratory results usually look like those presented in Table 1. When looking at such tables we should concentrate on the most important elements, which are the followings:
– Crude protein: it is a measure of the protein content. Unfortunately it is not very accurate since it estimates the protein content based on the nitrogen present in the feed. Therefore, non-protein nitrogen (NPN, e.g. urea) will also be measured as protein. You need to be very careful when interpreting crude protein values, especially if NPN is present in the feed. Protein content in a feed should never be lower than 8, but values above 12 are needed for growth.
– Crude Fibre: it is the traditional way of measuring the fibre, it gives an idea of the bulk. In a complete feed the fibre should be below 25-30%, however in forages and straw used as source of fibre it should be slightly higher (30-40%).
– Neutral Detergent Fiber (NDF): it measures three components of the fibre: hemicellulose, cellulose, and lignin. Their values in forages and straws can be very high (up to 80%), but values below 70% are desired. In a complete feed, they should be below 50%, considering values between 30% and 40% optimal.
– Acid Detergent Fiber (ADF): it measures two components of the fibre, cellulose and lignin, therefore it is always lower than NDF. The values in forages can reach 40%, but in a complete feed the values should be below 30%.
– Acid Detergent Lignin (ADL) or just Lignin is not a carbohydrate. It is however strongly linked to them hampering carbohydrates digestibility by microorganism naturally present in the GUT of the animals. It is recommendable that lignin content is below 5%.
– Organic Matter Digestibility: it gives an idea of the digestibility of the feed. It answers the question “which percentage of the nutrients present in the feed are available to animals?”. It should be above 60% although above 50% could work as survival ration.
– Metabolizable Energy (ME), usually measured in KJ/Kg, is the energy needed by the animal to carry out activities: breath, move, growth, in other words, it is the fuel of the body. 7 KJ/Kg is considered as survival ration, for good growth rates values should be above 9.
|Main analysis||Corn||Molasses||Soybean meal (dehulled)||Yellow lupin (seeds)||Buffalo grass||Corn stover|
Table 1. Source: feedipedia.
With the knowledge you have just acquired you can now interpret Table 1 and arrive to the following conclusions:
1. Corn is a good source of energy with moderate protein content
2. Molasses is a good source of energy but its protein content is very low
3. Soybean and lupin (seeds) are extremely rich in protein and also contain good ME values, however their energy content is coming mainly from proteins. Proteins are not direct energy sources, they should be converted, and therefore corn and molasses are preferred energy sources
4. Corn, molasses, soybean and lupin, although nutritious and energetic, contain extremely low fibre. Fibre is needed for the correct functioning of the body; therefore a fibre source should be added when using these elements
5. Grasses are better fibre sources than crop residues (straws and stovers) since the fibre of the grass is more digestible (hence the higher ME) and contain more protein. However, under harsh environmental conditions straws can also work, especially if appropriately treated (urea, NaOH…)