Carbohydrate Fractions in Dairy Rations

James D. Ferguson, VMD, MS
University of Pennsylvania
School of Veterinary Medicine

In General the Typical Dairy Ration is:

• 70% Carbohydrate (CHO)
• 18% Crude Protein (CP)
• 5% Fat (EE)
• 7%  Ash (ASH)
• TC = 100 - (CP + EE + Ash)

Goal: Provide low fill, highly fermentable diets that result in consistent ruminal fermentation over time (M. Allen)

• Low fill – maximize DMI
• Highly fermentable – maximize microbial synthesis maximize available energy
• Consistent over time - minimize variation in rumen pH
  • consistent absorbed nutrients for milk synthesis and liver function

Form and type of CHO in diet has a major impact on all the above

Often the primary feeding management problem on dairy farms is blending and mixing carbohydrate sources to achieve the above goal.

Problems may relate to:

1. The total amount of CHO in the diet ; Chemical content of CHO in the diet
2. Type of CHO - Structural versus Nonstructural; Not all CHO has the same fermentation pattern/rate in the rumen
3. Physical form; particle size and processing of the CHO
4. Sequence of feeding - component fed herd; Forage --> concentrates and amount per feeding

Production and health problems associated with CHO feeding:

1. Low Butterfat Test
2. Laminitis / foot problems
3. Low/irregular dry matter intake
4. Ketosis and metabolic problems
5. Primary rumen acidosis and secondary conditions
   • rumen parakeratosis
   • liver and lung abscesses
   • epistaxis

Forms of Carbohydrate in Dairy Rations:

• Total Carbohydrate (Nitrogen Free Extract)
• Fiber, starch, sugars, pectins, b-glucans (silage acids)
• Structural and Nonstructural carbohydrate (fiber and nonfiber carbohydrate)
  • Structural - neutral detergent insoluble fiber Hemicellulose, cellulose, lignin (NDF)
  • Nonstructural (Nonfiber carbohydrate) (neutral detergent soluble); Sugars, starches, pectins, b-glucans, fructans

Forms of carbohydrate are defined on solubility in neutral detergent solution and/or acid detergent solution

Insoluble components - NDF or ADF, structural
Soluble components – NFC, NSC, nonstructural

NDF solubles usually ferment at a faster rate than NDF insoluble components

Degree of lignification influences the proportion of NDF which may be fermented

Lignin content is a function of crop, hybrid, stage of maturity at harvest, weather conditions

In high producing cows, desire NDF with high degradation rate and rapid turnover (low fill factor)

Fiber carbohydrate (Structural carbohydrate)

1. Source - cell wall  
   1. structural carbohydrate
     
2. Hemicellulose, Cellulose, Lignin  
   1. Neutral detergent insoluble (NDF)
   2. Acid detergent insoluble (ADF) Cellulose and lignin

Importance of physical form of fiber: Long fiber

1. stimulate chewing
2. formation of rumen mat for trapping small particles
3. consistent fermentation throughout the day
4. stimulate chewing for saliva production buffering
5. too little versus too much

Non-fiber carbohydrate (Nonstructural Carbohydrate)

NFC - calculated value (DM - CP - NDF- Ash - Fat)
NSC - measured enzymatic value (starch + sugars)

NFC

• Calculated value
• Starches, Sugars, Pectins, b-glucans, fructans, and Silage Acids
• Neutral detergent solubles

NSC

• enzymatic assay = (starches and sugars) Depending on assay method and feed may include starch, sucrose, and fructans

Pectins are readily fermentable in the rumen and total tract digestibility is high. However, rate of fermentation of pectins decreases as rumen pH declines, unlike for starches, therefore they may be somewhat protective of pH decline.

Fructans ferment like starch and are found in grasses NSC may be sucrose, starch, and fructans

NFC calculated values will include sugars, starch, and water soluble fiber (pectins and b-glucans). However, the calculation can also contain non-carbohydrate fractions

CP contains NDF-CP and NDF may also contain NDF-CP depending upon the method of analysis used in the lab, so the NFC calculation may double subtract NDF-CP

In addition silages contain acids, which will appear in the NFC calculation and these contribute little to microbial protein synthesis

Therefore, calculated NFC values need to be interpreted with caution – they may accurately reflect rapidly fermentable carbohydrate sources or may not

Chemical and Physical descriptions

1. chemical form- SC vs NSC: main effects
   • SC     - rumen pH, rumination
   • NSC - microbial growth
2. physical form
   • SC     - chewing, rumen turnover, rumen mat formation
   • NSC - rate of degradation or fermentation of carbohydrate and microbial yield

Associations:

1. ADF
   • NeL (net energy lactation)
   • correlates negatively with digestibility
2. NDF
   • associated with rumen fill
   • correlates (-) with dry matter intake
   • correlates (+) with rumination
   • correlates (-) with energy content
3. NDF is 8-12% higher than ADF in legumes
4. NDF is 20-30% higher than ADF in grasses

Relative fermentation in the rumen:

Lignin negatively correlates with amount fermented
Hemicellulose negatively correlates with rate of  fermentation

Grasses versus Legumes

Legume - rate is rapid, extent is limited

Grass - rate is slower, extent is higher

Higher lignin – alfalfa
Higher hemicellulose – grass
Legumes tend to lower rumen fill and higher turn over than grasses, therefore legumes preferred in high producing cow rations

Impact of rumen retention time on digestion (18 - 24 hours, legume is higher)

Fermentation of Carbohydrate in the rumen has a major impact on microbial synthesis and flow of microbial protein to the small intestine.

10 kg of NDF         Kd - 5%/h      181 g MN
10 kg of starch       Kd - 15%/h    262 g MN

Balancing the rates of fermentation of starch and fiber is essential to optimize microbial flow and energy available to the cow.

Simplistically, rumen microbes may be considered as two pools, SC fermentors and NSC fermentors. However, some bacteria are protein fermentors. In addition, protozoa and fungi play important roles in starch and fiber digestion. Fiber bacteria grow slowly, 8-10 hours to double, whereas NSC bacteria grow rapidly, doubling in .25 to 1 hr.
 
MN, g/d = 181.581 + 89.25*OM - 4.16*OM2           

Maximum rates of microbial protein synthesis per kg of OM fermented is 24.5 - 26.4 g of microbial N / kg OM digested
at an optimum level of 11.66 kg - 13.73 kg of digested OM per day or

0.30 lb microbial protein / lb Fermented CHO
requires N - 10-13% DIP as % of DM

Balance amount of fiber and available energy   and protein in dairy rations to optimize N utilization and microbial synthesis.

In general:

1. The percentage of carbohydrate digested in the rumen correlates with the percent of NSC in the dietary carbohydrate.
2. Microbial crude protein efficiency is not effected by the percentage NSC in the ration
3. The yield of microbial crude protein is influenced by the total amount of fermentable carbohydrate in the ration
   • Balance the NDF and NSC content
   • Slower fermentable CHO sources reduce MCP
   • Rapidly fermentable CHO sources increase MCP
   • Too much and too rapid fermentable CHO sources can cause rumen upsets
4. The percentage of carbohydrate fermented in the rumen is influenced by the content of rumen degraded protein in the ration - especially true protein
5. Microbial crude protein production efficiency is a function of the content of rumen degraded protein (DIP) in the ration - 10 - 13 % DIP of ration DM

Relationships of NDF in diets (Sauvant, ADSA 2000)
NDF as percent of DM
DMI, kg = 19.1 + .269*(NDF) - .006*NDF2

Carbohydrate and rumen pH:

Maintenance of rumen pH is complex

• Salivary buffering
  • Chewing
  • Eating and rumination
• Absorption of VFA from rumen
  • Papillae surface area
• Rate of fermentation of carbohydrate
  • Type of grain and processing

Measuring rumen pH is difficult

• Normal diurnal fluctuations and variation with time postcalving
• Rumenocentesis is of limited value
  • Complications of deep body wall abscesses

Adaptation to high NSC diets

• Avoid sudden changes from low to high NSC ration

   

Maintain adequate NDF and “chewiness” of diet             

Use of buffers in ration

• Na bicarbonate - 4 to 8 ounces/day

Fractions of CHO in CPM-Dairy

Analysis:

ADF
NDF
Lignin 
Starch
Sugar
Fermentation analysis – total acids

NDF 30 hour digestion – rate:

Ether extract
Ash
CP (fractions)

Rules of Thumb:

Fiber: NDF in ration

Minimum and maximum to maintain rumen mileau and ensure sufficient energy intake

Physical form of NDF – many ways to try to measure

PSU shaker box – residue on top two screens >=60%

Total NDF

Min 28% of DM Total NDF (NRC - TOO LOW) ignores physical form

32 - 35%  total NDF especially with chopped forages

Forage NDF >= 21% forage NDF in ration DM; 75% of NDF from forage     

Physically effective NDF: 22% of DM

Effective NDF (retained on 1.18 mm screen)
Min 22% of DM to account for physical form
Problem – how to measure this

Max 

1.0 to 1.3% BWT upper limit, lower limit .85 to 1.1% BWT  primiparous animals

Effective NDF guidelines

Grains, effective fiber ranges:

100% Whole cottonseeds
100% Whole soybeans
100% Whole dry corn
40-60%  coarse grains
30-40% ground or finely rolled grains
20-40%  beet pulp, citrus pulp, wheat bran cotton seed meal, soy bean meal
<20% brewers, distillers, soy hulls, mids hominy

Nonstructural carbohydrate:

Minimum and maximum (NFC % of DM)

30-40% of ration dry matter

24-30% of DM as sugars and starches

3 - 5% sugars (5 - 10%)
19 - 27% starch

19% is too low for high producers
27% upper limit

40 - 45% of DM with high haycrop silage rations or a lot of by product feeds

Processing:

rapid fermentation:

finely ground HMSC or HMEC
barley, wheat,               
steam flaked corn
roasted corn

sorghum – need to steam flake

Trouble shooting

Observe chewing activity

More than an hour after eating
50% to 75% of cows chewing

Observe manure

Looseness/tightness
Grain/fiber presence

PSU analysis of TMR

5 – 10 % on top screen (>19 mm)
40 – 55% on second screen (8 to 19 mm)
>= 60% of ration on top two screens
More than 10% on top, potential sorting
problem

PSU analysis of forages

10 % of CSG and Haylage on top screen
>=60% on top two screens

Fat/protein inversions (protein>fat in milk)

Up to 15% is normal on any test day

If rations are too fine:

Multiple options may be taken. One of or combinations of any of the below.

Feed more total forage

Add chopped hay/long material

Utilize nonforage fiber sources

Increase total NDF

Feed more frequently and push up feed more often

Guidelines for NDF and NFC

NDF                                NFC
Min         Max                        Min         Max
Lactating cows
Early/             30            36                    38            42
90+                  30            36                    38            42
70                    32            36                    37            42
50                    35            39                    32            40
30                    38            42                    33            38

Far-off dry cows    42            50                    30            33
Close-up dry cows 42            47                    32            36

Heifers, body weight, 1.8 lbs gain/day
450                                  40                                    38
650                                  44                                    34
890                                  44                                    34
1100                                40                                    36