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The
effective fiber and rumination What is Effective Fiber: The term “effective fiber” can be defined as the ability of a fiber source to stimulate rumination. Various metabolic disorders can result if minimum effective fiber levels are not met. At low fiber intake, rumination decreases and thus, saliva production decreases, rate of passage from the rumen slows down and rumen motility can be decreased. These factors can results in rumen acidosis which will lead to decreased feed intake, decreased dry matter digestibility, laminitis and rumen parakeratosis. Milk fat depression is also associated with insufficient rumination. The three major characteristics of a feed source that contribute to its effectiveness at stimulating rumination are: chemical composition (fiber level), functional specific gravity and particle size. Effect of Chemical Composition on Rumination: Rumination activity is directly related to the NDF content of a feed. The NDF component is made up of three major constituents: cellulose, hemicellulose and lignin. Of these three, cellulose and hemicellulose are potentially degradable by the rumen microorganisms. Lignin provides rigidity to the cell wall of plants and is the most limiting factor to nutritional availability and digestibility of fiber by rumen microorganisms. As plants mature, the proportion of lignin relative to the total fiber content increases. This means that the rumen bacteria are able to digest less fiber and the cow will have to spend more time ruminating feed to allow it to pass out of her rumen. Diets containing high fiber forages are likely to inhibit intake. In ruminants, the volume of the rumen limits feed intake. Furthermore, a cow will only ruminate for approximately 11 hours per day. If the cow is unable to reduce the particle size of the ingested fiber sufficiently over a 24 hour period, passage out of the rumen will be slowed. As a result, intake will be depressed until the fiber can be ruminated to a size that will pass out of the rumen. The protein content of a feed is also a factor to consider. The rumen available protein is degraded to ammonia, which can affect the buffering capacity of the rumen and alter rumen pH. In addition, enough protein needs to be available to maintain high microbial growth rates. If degradable protein is not available to the microbes, ruminal fiber digestion may be depressed because of decreased microbial growth. Effect of Specific Gravity on Rumination: Functional specific gravity is another important characteristic of forage particles that contribute to their effectiveness. At an early growth stage, the size of the plant cell becomes fixed. As maturation occurs, the cell wall will thicken, become more rigid and intracellular space will decrease. This thickening will cause an increase in the specific gravity of the plant cell (i.e. cell becomes more dense). The specific gravity of a forage particle can only be changed when the cell structure is collapsed. This occurs during mechanical grinding, pelleting or rumination. Particles in the rumen tend to be stratified in relation to their specific gravity. The lighter particles float at the top and probably get caught up in the rumen mat. The heavier particles sink straight to the bottom of the rumen and are very unlikely to be ruminated. There are many factors that influence the functional specific gravity of a particle. Particle size is a major factor. As particle size of forage decreases, its specific gravity increases. Part of the function of rumination is to reduce the particle so that it has an appropriate size and specific gravity to pass out of the rumen. This is how long hay escapes the rumen and does not remain floating at the top forever. Read more about Rumen Physiology and Rumination Particle Size Rumination is the main source of feed particle size reduction. Mastication during eating and microbial digestion also reduce feed particle size, but to a much lesser extent. The average particle size leaving the rumen via the reticulo-omasal orifice is less than 1mm. As the majority of the feed entering the system is much larger than that, it is easy to see the great importance of rumination. Recently attention has been focused on optimal feed particle size for two major reasons. One, TMR mixing frequently results in particle size reduction of forages. Secondly, the smaller the particle size of a forage, the more likely it is to undergo an optimal ensiling fermentation. Another issue with forage particle size is that very fine particles will increase rate of passage through the rumen thus increasing intake, at least initially. However, this is accomplished at the expense of digestibility, since residence time and microbial exposure are shortened. A strong direct relationship between particle size and rumination time has been well documented. There is also strong evidence to indicate that particle size plays a significant role in the maintenance of rumen health. Many studies have demonstrated the relationship between reduced particle size and the increased incidence of milk fat depression. As particle size decreases, rumen pH and acetate: propionate ratios tend to decrease as well, suggesting rumen health and productivity will be compromised. The particle size at which rumen health is maintained is widely discussed but remains undiscovered. Varying research suggesting critical particle sizes of anywhere from 6.4 mm to 9 mm to between 10 and 20 mm illustrates how little is currently known. Read more about Penn State Particle Size Separator What are the cows saying? More about this topic: Particle Sizing: A Tool for Evaluating Forages
and Total Mixed Rations Balancing Rations for Forage Quality Effective Fiber in Barley-Based Diets |
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