Fibrolytic microbial populations are vital to maximizing forage digestion
Ruminants depend on microbial fermentation within the rumen to acquire energy from plant material (Oba M. and Allen M. S. 1999).
The different fractions from plant cells walls are not entirely physically accessible and achieve various degrees of digestibility in the rumen.
Rumen fungi attached to a plant cell wall ©INRA
To improve animal productivity, a portion of the forage diet is increasingly substituted with readily-fermentable carbohydrates. However, the supplementation of diets with readily-fermentable carbohydrates is known to depress rumen fiber degradation (Moorby J. M. et al., 2006).
Additionally, the major fiber-degrading bacterial species Fibrobacter succinogenes, Ruminococcus albus and R. flavefaciens, as well as rumen fibrolytic fungi, are particularly vulnerable to rumen pH at 5.8 or lower.
The challenge for ruminant nutritionists is to maximize a balanced nutrient intake and availability, digestion and ultimately the efficiency of this process to convert to milk, meat or wool.
Digestion of fiber in the rumen can depend on carbohydrate type
Fiber degradation depends on rumen pH
| Indicators and risk parameters |
General reasons |
|---|---|
| Decreased animal performance | – Reduced average daily gain and feed conversion ratio may be due to impaired rumen fermentation in beef cattle. – Low milk production, milk fat and a reduced fat/protein ratio may be due to impaired rumen fermentation in lactating dairy cattle (Britt J. S. et al., 2003), (Allen M. S. 1997), (Sauvant D. and Peyraud J. L. 2010). |
| Liquid manure & undigested grains | Undigested processed grains in the feces because of poor rumen efficiency may be due to an increased passage rate due to an imbalanced or low diet digestibility (Hall M. B. 2002). |
| Loss of body condition | Thin animals can indicate poor rumen efficiency due to poor diet digestibility and decreased intake (Zaaijer D. and Noordhuizen J. P. T. M. 2003), (Butler W.R. and Smith R. D. 1989). |
| Heat stress | Heat stress (temperature and / or humidity) increases the risks of acidosis and low fiber degradation because: – Eating behavior is negatively affected: cattle prefer to eat during cooler times of the morning and later evening. – Dry matter intake is decreased: cattle sort the diet with a lower proportion of forage and higher levels of fermentable carbohydrates. – High loss of saliva (from drooling and open-mouthed breathing) in hot weather decreases the amount of natural buffers to the rumen (Burgos et al., 2011). |
FAQ About Poor Fiber Degradation Issues in Ruminant
Poor fiber degradation is primarily caused by:
- Low rumen pH (below 5.8), which inhibits fibrolytic microbes
- High levels of rapidly fermentable carbohydrates in the diet
- Heat stress, which alters feeding behavior and reduces saliva buffering
It can lead to:
- Reduced average daily gain and feed conversion in beef cattle
- Lower milk yield and milk fat in dairy cows
- Increased undigested grains in manure
- Poor body condition
Strategies include:
- Maintaining optimal rumen pH through diet formulation
- Avoiding excessive starch or sugar in the ration
- Using feed additives like rumen specific live yeast or fibrolytic enzymes
- Mechanical processing of forages to reduce particle size
NDF, ADF, and ADL are important parameters used to evaluate the fiber content and quality of animal feed, particularly for ruminants:
- NDF (Neutral Detergent Fiber):
- Definition: NDF measures the total fiber content in the feed, including cellulose, hemicellulose, lignin, and silica 5.
- Importance: It is an indicator of the feed's bulkiness and how much the animal can consume. Higher NDF values generally mean lower feed intake and slower digestion.
- ADF (Acid Detergent Fiber):
- Definition: ADF measures the less digestible parts of the plant, primarily cellulose and lignin.
- Importance: It is used to estimate the digestibility of the feed. Higher ADF values indicate lower digestibility and energy content.
- ADL (Acid Detergent Lignin):
- Definition: ADL measures the lignin content in the feed, which is the indigestible part of the plant cell wall.
- Importance: Lignin content affects the overall digestibility of the feed. Higher ADL values mean lower digestibility.
Understanding these parameters helps in formulating balanced diets for ruminants to ensure optimal health and productivity.Fiber degradation depends on rumen pH