Some considerations on the nutritional quality of forage crops.

in StemSocial2 months ago (edited)
Dear readers and livestock lovers, as we all know, ruminants are consumers of forage plants by nature, that is why pastures and forages become the main food to cover their basic needs such as maintenance, growth and body development. According to Calsamiglia (1997), this dry matter is composed of organic and inorganic matter. Organic matter contains elements such as carbohydrates and proteins, and inorganic matter contains minerals; these elements are important in the nutrition and physiology of ruminants.

Herd of GYR cattle consuming Megathyrsus maximus grass


Image design @amestyj with photograph of the puerta parra cattle ranch

For this reason, it is important to study in depth the nutritional quality of pastures and which are the most used methods to know the percentage of protein, carbohydrates, among other elements, which according to Rodriguez (2013), will allow an efficient management of the same, since, through these parameters, some pasture management can be established, such as the days of rest of the pasture, in addition to knowing what are the deficiencies of the crop.

Is fiber the same as cell wall in forage crops?

To begin with, it is important to point out that plant cells have a cell wall, which is traditionally known as fiber and, according to Herrera (2006), is made up of a group of elements that in the diet are relatively resistant to digestion and are slowly and only partially degraded by ruminants.

On the other hand, Van Soest (1994), pointed out that from the point of view of plant structure, the term vegetable fiber is synonymous with cell wall, but from the nutritional point of view, it is an element that has a certain nutritional value and fulfills certain functions in the digestive and productive physiology of ruminant animals. In the same sense, it is of relevance to know which are the elements that conform the cell wall, based on what Herrera pointed out, the following are found:

Cellulose: Natural cellulose is a homopolysaccharide (composed exclusively of glucose molecules), insoluble fibrous, which is not easily degraded by the action of enzymes and is made up of glucose units.

Hemicellulose: Hemicellulose: hemicelluloses constitute 10 to 25% of the dry matter (DM) of forages, they are a group of monosaccharides soluble in basic solutions and capable of binding to cellulose through hydrogen bonds. According to Bach and Calsamiglia (2006), in ruminants cellulose is usually more digestible than hemicellulose.

Lignin: Lignin is the only polymer in the cell wall, which tends to fix other polymers in place, excludes water and makes the cell more rigid and resistant against various agents such as bacterial enzymes, thus exerting a direct negative effect on the total digestion of the animal. In tropical pastures, the concentration of lignin depends on the species and the phenological stage in which it is found, since the greater the maturity, the higher the concentration of this element.

Diagram of the plant cell wall


Public domain image LadyofHats and Miguelferig, 2015

The aforementioned elements are part of the pasture fiber and fiber has an important function in ruminants, since it is a fundamental component of the cattle diet, the main function is to stimulate chewing and saliva production to promote good rumination and maintain ruminal pH, which favors rumen health and the productive behavior of the animals.

What are the methods that can be used to determine fiber in pastures?

In the same vein, it is necessary to know which methods can be used to determine the fiber in pastures, taking Möller (2014) as a reference:

- Through the Weende method, crude fiber is determined by acid hydrolysis with 1.25% H2SO4 (sulfuric acid) for the extraction of sugars and starch, followed by alkaline hydrolysis with 1.25% NaOH (sodium hydroxide), which removes proteins and part of the hemicellulose and lignin. Crude fiber is commonly used to evaluate the quality of plant foods on the premise that it is the least digestible part of the food.

This method has been criticized by some researchers, because in alkaline hydrolysis a high proportion of lignin is solubilized, according to some authors in fibrous forages the proportion of solubilized lignin is higher than 50% of the lignin present. In these cases, the digestibility of crude fiber is higher, which is not 100% correct, since part of the lignin element that is indigestible in the rumen of ruminants is solubilized, therefore, it does not show in its totality the elements that compose the fiber.

- There is also the Van Soest method, which, due to the inaccuracy in the determination of crude fiber, Van Soest developed the analysis known today as the Van Soest method, which divides fiber into: neutral detergent fiber (NDF) and acid detergent fiber (ADF).

*The fraction known as neutral detergent fiber (NDF) is made up of the elements of the cell wall (cellulose, hemicellulose and lignin), its name refers to the fact that it is a fiber obtained by boiling a sample in a solution of neutral detergent, through this fiber a complete estimate can be made of the cell wall (fiber) of the forage material and this is related to feed intake, i.e. it is associated with the filling of the animal's stomach.

*On the other hand, the acid detergent fiber ADF is made up of cellulose and lignin, its name refers to the fact that it is a fiber obtained by boiling a forage sample in an acid detergent solution, when this solution is applied, the hemicellulose dissolves, leaving indigestible elements such as lignin.

The range of the NDF for its respective analysis according to the American forage association is between 41 and 65%, and the ADF presents a range between 31 and 45%. The bovine is selective and will not consume high amounts of a material with prolonged maturity, in the case of a mature material with high amounts of NDF for example 58%, voluntary consumption decreases since the ruminant with few bites will feel full due to the high levels of fiber; in the case that the ADF is found with high levels for example 43% we would be in the presence of a material with high percentages of lignin and with a low percentage of digestibility.

Classification of NDF and ADF assigned by the American Forage Association.


Image design by @amestyj

Dear readers, with everything described above, the importance of knowing the nutritional composition of pastures is evident, since they are quality indicators that allow making the right decisions on the zootechnical and agronomic management of pastures, allowing ruminants to consume forages of optimum quality to increase the productive levels of livestock systems.

Bibliographic references
Rodríguez, A. (2013). Pasture management practices and milk productivity in the Maracaibo Lake basin. In scientific notebooks girarz (Comp.), Management of tropical pastures and forages (pp. 105-115). Maracaibo: Astro Data, S.A.

Van soest, P. (1994). Ecological nutrition of the rumen (2nd ed). Cornell University prees.

Calsamiglia, S. (1997). New bases for the utilization of fiber in ruminant diets. Madrid, Spain: XIII FEDNA specialization course. Autonomous University of Barcelona.

Bach, A and Calsamiglia, S. (2006). Fiber in ruminants. Autonomous University of Barcelona.

Moller, J. (2014). Comparison of methods for the determination of fiber in feed and food. FOSS, Barcelona Spain.

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Are you saying that the cellulose content of a pasture is the most important content to consider when feeding our livestocks?

Greetings my dear @ummar, thank you for leaving your concerns about the article, this will certainly strengthen the content.

Well, when I referred to cellulose, I meant that it is often more digestible than hemicellulose in ruminant animals. When handling cattle in the paddocks we must offer them pastures that are in a favorable phenological stage, before flowering would be ideal, this would be an indicator that the plant is not very mature, since, when very mature pastures begin to intertwine in the cell wall the lignin with the structural carbohydrates present as cellulose and hemicellulose, this causes the walls to thicken and it is difficult to find elements inside the cells such as proteins and soluble carbohydrates, therefore the digestibility is late.

It is there where the zootechnical management comes into play to give the grass the days of occupation and rest and in this way you have in the pastures a pasture that can provide adequate nutritional elements for the maintenance and production of the animals.

Thank you very much for your question my friend, have a great weekend.

That's an interesting and plausible explanation. Thanks for clarifying

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