Ruminant nutrition knowledge（1）
1. Protein
– Rumen degradable protein (RDP): refers to the protein that can be decomposed and utilized by rumen microorganisms after the feed passes through the rumen.
– Rumen non-degradable protein (RUP): refers to the protein that will not be decomposed and utilized by rumen microorganisms after the feed passes through the rumen.
– Metabolic protein (MP): refers to the protein that reaches the small intestine and can be digested and absorbed by beef cattle, including rumen microbial protein and rumen non-degradable protein.
– Nitrogen MCPn: refers to the total amount of rumen microbial protein that can be synthesized by rumen microorganisms using the degradable protein provided by the feed, provided that other nutrients are met.
– Energy MCPe: refers to the total amount of rumen microbial protein that can be synthesized by rumen microorganisms using the energy provided by the feed, provided that other nutrients are met.
– Rumen nitrogen energy balance: RNEB = MCPn – MCPe, used to consider whether the nitrogen and energy contained in the feed can just meet the needs of rumen microorganisms to synthesize microbial protein.
If the RNEB value = 0, or close to 0, it means that the rumen nitrogen energy of the formula is basically balanced.
If the RNEB value > 0, it means that the rumen nitrogen energy of the formula is unbalanced, and the degradable protein provided to the rumen microorganisms is relatively excessive, or the energy provided is insufficient.
If the RNEB value < 0, it means that the rumen nitrogen energy of the formula is unbalanced, and the energy provided to the rumen microorganisms is relatively excessive, or the degradable protein provided is insufficient.
– Consequences of rumen nitrogen-energy imbalance:
[1] Rumen microorganisms cannot synthesize the maximum amount of microbial protein, affecting the production level of beef cattle.
[2] Excess nutrients that cannot be utilized will result in nutrient waste and may also increase formulation costs.
2. Carbohydrates
– Carbohydrates are the main source of energy in feed. In addition to providing energy for rumen microorganisms and feeding animals, they also provide effective fiber needed to stimulate rumination and rumen peristalsis.
– Carbohydrates are roughly divided into two parts: non-fibrous carbohydrates (NFC) and neutral detergent fiber (NDF).
– NFC, also known as non-structural carbohydrates (NSC), is usually found inside plant cells and is easier to digest than NDF.
NFC calculation formula: NFC = 100 – (CP% + NDF% + Fat% + Ash%).
– NDF exists in the cell walls of plants, including cellulose, hemicellulose and lignin, and is digested relatively slowly in the rumen.
– Carbohydrates include six major components: organic acids (OA), water-soluble carbohydrates (WSC), starch, medium-wash soluble fiber, available NDF, and unavailable NDF.
The first four components belong to NFC, and the last two components belong to NDF.
– Organic acids (OA): acids produced by silage fermentation, as well as organic acids present in forage.
Ideal silage fermentation can produce more than 3% lactic acid, which can be quickly absorbed by animals in the rumen; the ideal silage lactic acid:acetic acid ratio should be >3:1.
Organic acids can only be used as energy by animals themselves, and they cannot provide energy for rumen microorganisms.
– Water-soluble carbohydrates (WSC): including monosaccharides, oligosaccharides and fructans, are energy sources that can be fully utilized by microorganisms in the rumen.
– Starch: includes amylose and amylopectin, the former has a slightly lower digestibility.
The endosperm of cereal seeds is an important place for the storage of starch granules. The endosperm is glassy and powdery. The former is hard and difficult to digest. The digestibility can be improved through steam flaking, gelatinization and other processing.
– Medium detergent soluble fiber: includes pectin, glucan, lactan, etc., mainly derived from leguminous forage, citrus pulp, beet pulp, soybean hulls, soybean meal, etc.
– Neutral detergent fiber (NDF): includes usable NDF (cellulose and hemicellulose) and unusable NDF (mainly lignin, which is not easy to digest).
Feeds with high NDF content include: forage, crop straw and some by-products (vinasse, cottonseed hulls, soybean hulls, beet pulp, second meal, etc.).
The digestible energy in most beef cattle feeds mainly comes from NDF, except for the case of fattening cattle fed high concentrate feed.
– Effective fiber (eNDF: This concept originally came from the formula of dairy cow feed and is used to describe the ability of a certain feed in the feed to replace forage while maintaining the same milk fat content.
The eNDF value of a feed depends on the particle length, buffering capacity, fermentation rate, etc. of the fiber it contains. There is currently no feasible method to measure the eNDF value.
– Physical effective fiber (peNDF): The ability of a feed to replace forage in stimulating rumination and rumen peristalsis is measured based only on the fiber particle size in the feed.
– Prediction of rumen pH: Since finishing cattle are fed high-concentrate feed, rumen acidosis is prone to occur. Therefore, it is necessary to evaluate the rumen pH based on the nutrient composition of the feed.
General requirements: The rumen pH of finishing cattle during the finishing period should be above 5.8, and the pH value in other stages should be maintained above 6.2.
There are currently two methods for evaluating rumen pH:
[1] Calculate rumen pH based on the roughage ratio (%DM), pH = 5.724 + 0.00963 Roughage ratio (%) Used when the roughage ratio of the feed is <50%DM.
If the roughage ratio of the feed is >≥50%DM, then pH = 6.2.
[2] Rumen pH is calculated based on the effective fiber (peNDF, referring to physically effective fiber) content, pH = 5.59 + 0.02189 peNDF(%) for diets with peNDF < 32.2%DM.
If diet peNDF > 32.3%DM, pH = 6.27.
【Special attention】 — Processing of grains and digestion sites of starch
Starch in feed has three digestion sites in the cattle body:
[1] In the rumen, it provides energy for rumen microorganisms to synthesize protein, with an efficiency of about 80%. The easier the grains are to digest after processing, the higher the proportion of them being utilized in the rumen.
[2] In the small intestine, it provides energy for the animal to gain weight, lactate, and gestate, with an efficiency of about 97%.
[3] In the large intestine, the efficiency is about 45%. Whole or coarsely crushed grains may be partially utilized in the large intestine, so the efficiency is relatively low.
From the above text, we can see that if starch is retained in the small intestine for digestion, the efficiency is the highest. If it enters the large intestine for reuse, the efficiency is very low.
Where the starch in the feed is digested is closely related to the processing of the grain seeds. The deeper the processing and the more exposed the starch is, the easier it is to be digested in the rumen.
Corresponding strategies:
[1] When formulating, if the rumen nitrogen energy balance value is > 0, it means that the rumen is not providing enough energy. It is necessary to increase the amount of starch seeds and further process them (such as steam flaking) to promote the synthesis of rumen microbial protein.
[2] For fattening beef cattle, if a large amount of starch is digested and absorbed in the rumen, volatile fatty acids (VFA) will accumulate rapidly, which can easily cause rumen acidosis.
Increasing the effective fiber content in the diet can move the starch digestion site from the rumen to the small intestine, thereby helping to reduce the risk of rumen acidosis.
[3] For breeding cows and growing cattle, since they are fed a high-roughage diet, the risk of acidosis is very low. It is recommended that grains be further processed to increase the utilization of starch in the rumen and the entire digestive tract.
