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Crude Fiber

In Vitro Incubation


In Vitro, Latin for ‘in the glass,’ refers to the simulation of an organic process performed in a lab setting. Conventional True Digestibility studies, such as the Tilley-Terry (1963), are performed in vitro and consist of anaerobic fermentation using either rumen inoculum or enzymes that mimic the digestion of a sample, such as feeds or forage. Through this process, researchers discern how easily and thoroughly samples can be broken down through digestion. Agricultural research, particularly in the areas of optimal feed production and animal health, benefits from these analyses.  


Studies such as the In Vitro Dry Matter Digestibility (IVDMD), In Vitro True Digestibility (IVTD), and Neutral Detergent Fiber Digestibility (NDFd) utilize different incubation and digestion times to ascertain different qualities of sample breakdown.  

In Vitro is a cheaper and faster alternative to In Vivo techniques of study, an advantage for researchers conducting regular analyses. Despite these benefits, the traditional In Vitro True Digestibility method is also labor-intensive, requiring sample transfer steps and consistent temperature control to complete filtration.  


Developed by Tilley and Terry (1963), this method measures apparent digestibility. There are two stages to the method. First, the sample is incubated for 48 hours in rumen fluid and buffer. Then, the mixture is digested in pepsin and HCl for 48 hours. Once the associated calculations are performed on the digested sample, digestibility is determined.  


The IVTD method (Van Soest, et al. 1966) is considered a true digestibility study as it involves correction for endogenous losses (apparent digestion with the IVDMD does not include this step). IVTD begins by incubating a sample in rumen fluid for 30-48 hours. Then, the sample is digested, after which an NDF extraction is performed. The NDF extraction replaces the pepsin and HCl step in IVDMD, providing the endogenous loss correction.  


Ascertaining the ND value of a tested feedstuff allows for the estimation of cell wall digestibility. This is achieved by drying, grinding, and incubating the sample in buffered rumen fluid at a series of time increments. The amount of neutral detergent fiber digested in the selected time frame provides the user with the NDFd value.  


Ruminant Nutrition


Ruminant animals are defined as herbivore mammals that derive energy from plant fibers (cellulose) and material. The term ruminant takes its meaning from the Latin word ‘ruminare’, or ‘to chew over again.’ These animals have four stomachs and digest their food through a fermentation process that first consists of rechewing consumed material.  

Unique ruminant microbes present in the digestive systems of these animals enable their systems to process grasses and fibers into energy. Many of these microbes are present due to the consumption of forages, which then thrive in the rumen of the animal and assist in the breakdown of nutrients. The rumen is a demanding microbial environment; bacteria not digested by the rumen become substrate and are evacuated.

The ruminant stomach system contains four chambers: the reticulum, rumen, omasum, and abomasum. Fermentation takes place primarily in the rumen, as microbes break down cellulose into carbohydrates and proteins and absorb the fatty acids that accompany them. These Cannula studies enable researchers to directly examine this process at work inside the rumen, which can hold thirty to forty gallons of digesting material.  


Ruminant studies are performed worldwide as researchers seek to gain more insight into the dynamics of digestion and fermentation. Understanding the nutritional needs of ruminants and measuring the quality of the forages they consume is paramount in cultivating both animal performance and health of rumen micro-organisms. Forage quality determinations not only seek to discern nutritional value but encompass palatability and intake.  

Forage Quality Crude Fiber Analysis  

Crude and detergent fiber analysis provide livestock farmers, feed producers, researchers, and regulatory bodies with critical information in understanding rumen fermentation and digestion. Feed quality determinations help identify and maintain the energy and health requirements set for the animal.  

There are three common analytical approaches to assessing fiber content in forage and feeds: Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), and Crude Fiber. While Crude Fiber analysis provides a broad fiber estimate, NDF and ADF (and subsequent Acid Detergent Lignin, ADL) analyses developed by Van Soest provide more detailed fiber values. Such digestibility studies aid in determining the most expedient feedstuffs for ruminants and their subsequent impact on human nutrition by proxy.  

In Vitro Fermentation  

Performed in a controlled environment, the in vitro fermentation analysis simulates rumen fermentation through the inoculation of rumen microbes. Rumen microbes produce gases such as carbon dioxide, hydrogen, and methane as they break down materials during digestion. Analysis of these gases can reveal information as to the fermentation quality and digestive effects feeds and forages can produce in the ruminant system.  

Gas Production Measurement

Gas production measurement tools help determine the fermentation quality of feeds and forages that ruminant animals consume. Gas production quality and quantity can reveal the nutritional and digestive value of certain foods on the ruminant system. Real-time accurate and precise data throughout these studies is important to see the full range of fermentation performance.