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2015-PPS1 Corn/hay – production & feeding efficiency

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7.1 About Principle Investigator
Short Curriculum Vitae
Education & work experience 
PhD degree in Agricultural Science at Wageningen University
PhD thesis Development of a model for the prediction of feed intake and energy partitioning in dairy cows
MSc degree in Agricultural Science at Wageningen University
BSc degree in Agricultural Science at Rijks Hogere Landbouwschool Groningen
Appointed as researcher since 1993 at Wageningen Livestock Research
Experienced specialist in ruminant nutrition, nutrition of dairy cows and dairy young stock

Field of expertise
Animal Nutrition and Feeding - Ruminant nutrition, nutrition of dairy cows and dairy young stock
Including ration and diet formulation and feeding strategies of dairy cows and dairy young stock
Animal Production Systems – Optimizing and developing ruminant (dairy cow production systems) 
Including forage production, forage utilization, silage making, grazing
Mathematics – Modelling intake and performance of dairy cows
 
Scientific publications are available at 
https://www.vcard.wur.nl/Views/Profile/View.aspx?id=2012&ln=eng


7.2 Objectives of the study
The goal of the project of the project is to improve and optimize the feed production and feed utilization in dairy cows through 
1) higher dry matter and nutrient yields by improved crop and harvest management (grass, alfalfa, corn, crop residues); 
2) minimizing losses during harvest, storage, improved silage preservation and feeding 
3) optimizing feed utilization by the animal through optimize diet formulation and allocation of feed maximize the conversion of vegetal biomass into milk and meat

7.3 Main report of the research
Crop maturity is important for: 
1)Dry matter yield
2)Feed digestibility
3)Feed composition
4)Nutrient yield
5)Losses during ensiling and feed-out

Optimizing crop maturity at harvest
1)Monitor your crops weekly
2)Alfalfa: cut between green bud and 10% flowers
3)Grass: before appearance of the ears (flowering)
4)Corn: > 30% Dry matter in the whole crop-> 1/2 milk line
 
Optimizing crop maturity at harvest
1)Corn: > 30% Dry matter in the whole crop-> 1/2 milk line
2)Too early (<30% dry matter) compromise
a)Dry matter yield
b)Feeding value: reduced energy and starch yield
c)Silage losses -> Effluent loss
d)Feed intake

Too late (>38% dry matter) compromise
a)Silage compaction
b)Losses during feed-out -> heating 
c)Feed intake

Harvest too early is more harmful than too late 

Make a good planning of harvest and logistics
1)Cut not more than you can handle
2)Grass & Alfalfa: Use well adjusted tedders and rakes
3)Capacity of harvest machinery should match with ensiling equipment (compaction vehicles)
4)Use precision chop harvesters for alfalfa corn silage 
5)Corn silage: theoretical lenght of cut 6-8 mm
6)Use a grain cracker / kernel processor clearance 1-2 mm
7)Assess chop size and kernel processing

Dry matter content at harvest 
Grass & Alfalfa: Field period is most important under wet conditions maximum 72 h drying on the field
Target dry matter contents at harvest:
Grass silage 35% - 45% DM
Alfalfa silage  32% - 38% DM
Corn silage 30-38% DM*
Use an additive below the target dry matter content. Wet alfalfa silage: provide extra sugar (e.g molasses) to help the lactic acid bacteria. Grass silage: use heterofermentative lactic acid bacteria, or molasses

Reduce ensiling losses
1)Keep air out of the silage
2)Seal the bunker silo’s silage clamps immediately
3)Match harvest capacity and compaction weight
a.Compaction weight ¼ of harvest capacity (tons/h)
b.Compaction vehicle should ride continuously
4)Use good quality plastic sheets
5)Protect plastic sheeting against damage (birds, wind)
6)Secure the plastic sheeting with sufficient weight  Use sand load, car tires, straps, or sand bags

Feed intake 
Feeds determined by Cow factors and Feed factors
Cow factors
a)Physiological status of the cow
b)Parity, Days in lactation, days pregnant
c)Breed, Size, BCS, Milk yield
Feed factors
a)Chemical composition
b)Dry matter content, Digestibility of Organic matter (DOM)
c)Ash, Crude protein, Starch, Sugars
d)Quantities of rumen by-pass starch and protein
e)Microbial protein and by pass protein
f)Feed intake by satiety inducing effects of feed composition

Rumen function and acidosis
The rumen is a complex organ
1)Rumen motility
a.Mixing the feed with rumen content
b.Fibrous feeds stimulate motility of the rumen and rumination
c.Motility induced by stimulation of receptors in the rumen wall
2)Rumination increase saliva production
a.Bicarbonate in saliva buffers rumen pH
3)Rumen pappilae increase surface
a.Absorption of volatile fatty acids through rumen wall 
b.Clearance rate of VFA from rumen affect rumen pH
c.Rapid clearance is important to avoid low rumen pH
d.Development of papillae important-> Absorption surface
e.Rumen papillae influenced by diet -> adaptation
4)Rumen pH
a.Fluctuate pH decrease after a meal
b.Large meals result in larger drops of rumen pH
c.Rumination helps buffering rumen pH through saliva production
5)Rumen acidosis
a.Acute rumen acidosis – “off feed syndrome” – Grain induced
Occurs sudden, only individual cows
b.Sub-acute rumen acidodosis SARA
Rumen pH <5.9 for more than 4 hours
Large proportion of cows in the herd
6)Prevention of SARA
a.Sufficient fiber in the diet, 
b.Frequent feeding of feed >3 times a day -> small meals
c.Avoid competition for feed
Feeding systems
1)Individual concentrate feeding
a.Better suited for smaller farms <500 cows
b.Investments in computers, concentrate feeders
c.Higher feed efficiency less over and under feeding
2)TMR
a.Group cows according milk production or stage of lactation, age
b.Form balanced groups minimize variation in groups

Formulation of TMR rations
1)Monitoring the cows - >Cow signals
a.Milk Production of cows,
b.Body condition score
2)Manure
a.Grain kernels, fiber - >cow signals
b.Consistency/texture of manure sticky thin fluid
3)Cow behaviour – rumination behaviour, rumen fill
4)Sorting of feeds
5)Amounts of feed consumed
6)Keep records!

Energy
1)Milk production
2)Milk composition
3)Calculate the energy requirements
4)Feed intake of the group

Protein
1)Metabolisable protein requirements
2)Chinese MP requirements (NRC system)
3)Crude protein
4)Shortage may impair fiber digestion 
5)Rumen microbes need N

Recommendations:
Early lactation (<120 DIM, high yielding)  >18% Crude protein
Mid and late lactation (>120 DIM) >16 % Crude protein
Dry cows (drying off – 2 week before calving) >14% CP
Other dry cows (< 2week before calving) like Early lactation

Starch
Recommendations:
Early lactation (<120 DIM, high yielding) >18% Starch in the diet
Mid and late lactation (>120 DIM)  <15 % Starch in the diet
Dry cows (drying off – 2 week before calving) no starch
Other dry cows (< 2week before calving) like Early lactation , so rumen microbes can adapt to the lactation diet

Particle size
Use chopped feeds
Prevents sorting by the animals
Improves mixing

Recommendations feeding TMRs
Feeding frequency
> 3 times/ day fresh feed
> 3 in between pushing the feed to the feed bunk
> 3 times feeding: smaller meals
Smaller meals less risk for SARA
Less competition at feed bunk, less fighting for feed

7.4 Conclusion
Good feeding management is a matter of low cost and high competence!

7.5 Appendix
7.5.1 Handbook Alfalfa
7.5.1.1 Alfalfa
Summary
Stage of maturity at cutting affects the annual dry matter yield per cut, the number of cuts and total dry matter yield. The stage of maturity at cutting has also major effects on the feeding value (Net energy, crude protein, fiber) of alfalfa hay and silage. The conditions during harvesting, as well as the type of cutting and harvest equipment and machine settings may affect the losses of leaves and thereby influencing feeding value. Furthermore, maturity at cutting affects also the persistency of the alfalfa stands.
Stage of maturity at cutting
The stage of maturity at has a major impact on the feeding value of alfalfa. The feeding value of alfalfa is strongly influenced by the leaf to stem-ratio and the fibre content of the stem fraction. The digestibility of the leaf fraction is approximately 85%, whereas the digestibility of the stem fraction is approximately 50%. Thus, a higher leaf to stem-ratio results in higher whole crop digestibility. The proportion of leaves in the total dry matter yield decreases and the proportion of stems increases with advancing maturity of the crop (Figure 7-1).
Figure 7-1 Effect of stage of maturity (x-axis) on the total yield, stem yield, leaf yield and digestibility
For the production of high quality alfalfa silage or alfalfa hay it is recommended to cut at an early stage of maturity when or when the first (green) flower buds are visible: the green bud stage. At the green bud stage, the organic matter digestibility (OMD%) varies between 70 and 75%. For the highest dry matter yield, alfalfa should be cut when 10% of plants is flowering. At this stage of maturity the plant has sufficient carbohydrate stores, necessary for a rapid regrowth after cutting. However, at this stage OMD% varies between 60 and 65%.
Cutting at an early stage of maturity results in a higher leaf to stem ratio and subsequently in a higher digestibility. However, cutting at an early stage of maturity results also in lower dry matter yields per cut. Whereas cutting at a late stage of maturity results in a lower leaf to stem ratio and subsequently to a lower digestibility, but with a higher total dry matter yield per cut. However, cutting at an early stage of maturity has also a disadvantage because it reduces the carbohydrate stores in the plant. Low carbohydrate stores reduce the growth rate of the regrowth, and consequently a reduced dry matter yield. A reduced growth rate also impairs the competitiveness of the alfalfa stand often resulting in a greater invasion of weeds. When the carbohydrate reserves are not sufficient restored before the winter season it may reduce winter survival of the crop. Therefore, repeated cutting at an early stage of maturity may compromise total dry matter yield per year. Farmers should find the balance between a high feed quality and a high dry matter yield. 
Research in the Netherlands at Wageningen UR showed that two cuts at an early stage of maturity (green bud stage) followed by late cuts (10% flowering) resulted in the best compromise between dry matter yield and feed quality (Table 7-1). 
At the end of the growing season, the crops taller than 15 cm should be cut before the winter in order to create a new spring regrowth without death stems and plant residues from the previous season. 

Harvest of alfalfa haylage and hay
Harvest methods and techniques are crucial in prevention of losses at the field and achieving a high  quality alfalfa haylage (wilted silage) or hay. It is important to minimize te losses of leaves and avoid contamination of haylage with soil. This requires adequate machinery and machine settings and rapid wilting and drying.


Cutting and conditioning

Alfalfa is usually cut using disc cutter bars (disc mowers) or sickle cutter bars (sickle mowers). Drum mowers are less suitable because higher losses of leaves. The knives must be sharp to avoid a ragged cut. A stubble height of at least 6 cm is recommended. Stubble height has little impact on the feeding value. The feeding value is slightly increased with higher stubble heights (Table 7-2). 
To improve drying speed, it is recommended to cut alfalfa when the crop is dry (no moist from dew or rain). Drying speed can be increased by wide swaths and the use of conditioners. There are two types of conditioners to be distinguished: roll conditioners and flail conditioners. In general, roll conditioners are preferred for alfalfa because lower losses of the leaf fraction. Roll conditioners crush and break the stems of alfalfa. Adjustment of roll conditioner (roll clearance, pressure and speed) affects the condition and drying speed. Swaths dry more rapid at the surface than at the bottom. Therefore, swath inversion machines which gently lift and invert the swath can be used for more uniform drying. Sometimes the crop is spread using a hay tedder machine for uniform drying. Hay tedders should only be used in a wet (green) crop with less than 30% dry matter. Using hay tedders in a dry crop cause loss of leaves resulting in a reduced digestibility and feeding value. 
To prevent losses of leaves, it is recommended to windrow alfalfa when the crop is still moist to prevent losses of leafs. Furthermore, it is important to check the setting of the windrow machinery. Losses of leafs can be reduced by a proper adjustment of the rakes, relative low ground speed and low rotation speed of the rakes.
For the production of alfalfa haylage (wilted alfalfa) silage, the time on the field between cutting and ensiling (field period) should be no longer than 2 days. 
For the production of alfalfa hay requires for at least 4 days good (dry, windy) weather conditions. Alfafa hay should be baled at a dry matter content of 80%. Below 80% DM, forced air ventilation of hay in necessary to prevent moulding.

Harvesting and ensiling
Precision chop harvesters are recommended to harvest alfalfa silage. Precision chop harvesters homogenise the silage by mixing the relative dry material at the surface and relative wet material at the bottom of the windrow. A well-mixed homogenous silage is advantageous for the ensiling process. Precision chopping is also advantageous for a dense packing of the silage which reduces air penetration of the silage. 
For lactic acid fermentation of the silage sufficient available sugars and anaerobic conditions are essential for a good silage preservation. Alfalfa is relatively low in sugar and relatively high in protein which are unfavourable conditions lactic acid fermentation and a rapid decrease of the pH in the silage. Adding sugar beet molasses or sugar cane molasses at a rates of 5% (of the dry matter) with dry matter contents above 35% and 10% (of the dry matter) for alfalfa silage with a dry matter content between 20 and 35%. For a good mixing of the molasses it is recommended to dose the molasses on top of the swath immediately before harvesting with a precision chop harvester.
For a good alfalfa haylage (wilted alfalfa silage) preservation the following rules should be considered. 
a)Cut the crop at early maturity
•From green bud stage to 10% flowers 
b)Aim at 35 to 40% dry matter at harvest
c)Use a precision chop harvester
•For better compaction and homogenisation 
d)Use molasses as an additive to provide sufficient sugars for lactic acid bacteria
•5% of the dry matter yield in alfalfa with more than 35% dry matter
•10% of the dry matter yield in alfalfa with 20 to 35% dry matter
e)Create anaerobic conditions
•Use heavy weight vehicles for a good compaction of the silage
•Seal the silage bunker within one day
•Use good quality plastic sheeting and protection sheets
Figure 7-2 Good compaction with a heavy weight vehicle


Alfalfa in dairy cow rations
Alfalfa haylage and alfalfa hay are suitable for all categories of ruminant livestock. As pointed out earlier, stage of maturity at cutting is an important factor for the nutritive value. In general, alfalfa haylage and hay is relative high in in protein, and digestible organic matter. Alfalfa is also a good source of effective fiber. Compared to corn silage, the net energy value of alfalfa haylage is lower, but the crude protein content is higher. 
If good preserved, alfalfa haylage and hay is a very palatable feed allowing high intakes. For dairy cows it is important to cut the alfalfa at green bud stage. Cutting at early maturity results in higher feeding value (Table 7-3). Moreover, early cutting was also associated with higher intakes and improved performance (Table 7-4). 

Compared to grass hay, alfalfa haylage and hay has a higher proportion cell contents and a lower proportion cell wall. Alfalfa hay contains more pectin than grass hay. Compared to grass hay alfalfa hay contains much less hemicellulose, but the proportion of in alfalfa. In general, the total digestibility of the cell wall components of alfalfa is lower than of grass hay. However, despite this lower digestibility, the digestion rate and rumen outflow of the cell wall components is higher compared to grass silage and grass hay. Because of the higher degradation rate and outflow from the rumen, the voluntary dry matter intake of alfalfa haylage and hay is higher compared to the intake of grass silage and grass hay.
Alfalfa haylage and hay can be used as the only forage in dairy cow rations. However, alfalfa haylage and hay is high in rumen degradable protein. To improve nitrogen utilization, alfalfa haylage and hay should be combined with forages and concentrates that provide sufficient rumen fermentable organic matter. For example, good quality corn silage (30-35% DM, 25-35 % starch) is a good combination with alfalfa haylage and hay. 
Alfalfa silage and alfalfa hay is good source of fiber for dairy cows receiving diets with a large proportion of concentrate. 


Alfalfa in diets for rearing calves and young stock
Alfalfa haylage and hay are very suitable for rearing calves and young stock. On diets with ab libitum good quality alfalfa haylage and hay it is possible to achieve a dry matter intake of 2% of the body weight. For young stock the recommended target growth rates are 0.85 kg per day for calves between 2 to 8 months of age, 0.7 kg per day for young stock between 9 to 15 months of age, and 0.6 kg per day for rearing heifers older than 15 months. 
With good quality alfalfa, rearing heifers older than 15 months can achieve a growth rate of 0.6 kg per day without supplementation of concentrate. However, it is necessary to feed them additional vitamins and trace minerals.  

7.5.2 Handbook Corn Silage
 7.5.2.1 Harvest
Corn silage is an import source of energy on many farms. It is important to harvest corn at the right time and according to the right procedure so that corn silage can be optimally utilized in a ration. In this chapter it is discussed which factors influence harvest time, how to determine harvest time, and the harvesting method. 
(1) Maturity at harvest
The optimal harvest time of corn silage is when the whole plant obtained its maximum nutritive value, when silage losses are minimal, and when livestock can utilize the crop best. In practice, these requirements are not met at the same time or at the same percentage of dry matter. The best harvest time is a compromise between these factors. 
The best compromise is achieved when the whole plant dry matter is around 36% of the fresh weight. This corresponds with a dry matter content of the cob (corn ears and husks) dry matter of 55 to 60 % and a dry matter content of the of 24 to 27%. The latter is realized when half to a quarter of the leaves remain green. Other factors that influence harvest time are the ability to harvest (stalk rot and lodging) and the accessibility of the field.

Ever early harvest due to early maturing corn varieties
① Maximum nutritive value
The maximum nutritive value of the whole plant is yielded when the whole plant dry matter is between 34 and 40%, which may vary between years. In years with favourable growing conditions the whole plant dry matter will be higher and earlier achieved in years than in years with less favourable growth conditions. The maximum nutritive value is obtained as a result of the dry matter yield and the digestibility of the crop and net energy per kg dry matter). 
Digestibility
The digestibility of corn silage is mainly determined by the amount of starch, cell wall content, and the digestibility of the cell walls. The composition of corn silage changes during ripening, and as a consequence digestibility will change. The digestibility of the stover reduces but the digestibility of the cob increases. First, this is caused by conversion of carbohydrates from the stover to starch in the cob. Sugar content reduces and starch content increases. Second, it is caused by reduction in digestibility of the cell walls in the stover.  
Loss of cell wall digestibility will be compensated under favourable conditions. Consequently, the whole plant digestibility will increase. Loss of cell wall digestibility cannot be compensated when conditions are unfavourable and the whole plant digestibility will decrease slightly. The annual average of digestibility remains constant during ripening. Early maturing corn varieties will yield a certain dry matter content early in the season and the chance of increasing whole plant digestibility will thus be greatest for these types of varieties. 
The composition of starches changes as well during ripening. The proportion or rumen by-pass starch increases. By-pass starch is not digested in the rumen but becomes available as glucose in the intestine.

② Minimize ensiling losses
Ensiling losses are the result of effluent losses and losses during silage fermentation. To avoid effluent losses the whole crop dry matter content should be at least 32%. The preservation losses are lowest with a dry matter content between 33 and 39%. There is greater risks of heating and moulding during feed out  with at a whole crop dry matter content above 36%. Good silage management will reduce the risks of heating and moulding. Important is a short theoretical length of cut (TLC, chop size) of 6 to 8 mm, dense compaction using heave weight compaction vehicles,  fill the silage bunkers with layers of corn silage, air-tight sealing with good quality plastic sheeting (0.1-0.15 mm thick), protection sheets to avoid damage of the plastic. 
To minimize the losses during ensiling and feed-out it is best to aim at a whole crop dry matter content between 32 and 36 %. 
If it is the case that no sufficient dry matter content of the corn silage can be achieved due to extreme conditions, it is necessary to aim for a dry matter content of at least 28%. Silage losses will be limited to 10% in this way. 

Optimum harvest time is when the crop has a dry matter content of 36%
③ Maximum utilization of nutritive value
Results from feeding experiments (Wageningen UR Livestock Research 2005) show that the utilization of corn silage by high yielding dairy is higher at a whole crop dry matter content of 36% compared to a whole crop dry matter content of 30%. 
A higher whole crop dry matter content results in a higher concentration of starch with are larger proportion of rumen by-pass starch. 
Harvesting at a later point in time corresponds with increased hardness of the grain kernels, and hence results in a decreased degradability. The kernel should therefore always be used. The grain kernels should be crushed in at least four parts in order to allow maximum utilization of the grain kernels. 

④ Harvest risks
The optimal harvest time is based on the maximum nutritive value which is achieved at 36% of dry matter content. However, other factors play a role and it may be necessary to deviate from this value. 
The risk of stalk rot (fusarium) increases when the dry matter content of the crop increases. Stalk rot affects the lower part of the stalk. As a result, the nutrient flow is hindered which results in plant death. The dry matter content of the crop increases and the nutritive value is influenced negatively. Sugars that are present within the plant are utilized by fusarium fungi which has a negative effect on the ensiling ability. Besides these negative effects, stalk rot increases the risk of lodging. Crops can also lodge due to lack of firmness. Lodging increases the risks of yield losses and soil in the pit.  
One last factor that influences harvest time is accessibility of the field which determines whether the crop is easy to harvest or not. The crop needs to be harvest as soon as possible when there is a risk of stalk rot, lack of firmness or a bad accessibility of the field. This, despite the low yield, dry matter content or quality of the crop.
(2) Harvest management of corn silage
① Determining of harvest time
The maximum nutritive value is reached around a whole crop dry matter content of 36% in situations where the risk of heating of the silage is low. In situations with a higher risks of heating  a whole crop dry matter content of 32% is recommend. Dry matter contents below 32% dry matter may result in large effluent losses. 

Dehydrated corn silage often has a lower dry matter content


② Estimation of dry matter content in corn silage
To choose the right harvest time it is important that the dry matter content is estimated well. 
The dry matter content of the whole plant is determined by the proportion opf grain , the dry matter content of the stover, and the dry matter content of the cob. 
The proportion of grain 
The proportion of grain as proportion of the total dry matter yield  is influenced by the growing conditions (weather, type of soil, and plant density) and by the crop conditions (leafiness of the the crop and and size of the cob). In table 7-6 below it is presented how you can translate conditions to cob share.
Dry matter content of the stover
The discolouring of the leaves and the juice flow in the stem determine the dry matter content. Table 7-7 presents the relationship of the state of the stover and the dry matter content.  
Dry matter content of the cob
The dry matter content of the cob can be estimated based on the milk line of the grain kernels. The milk line is the line between the firm starch and the milk part (see figure 7-3). The milk line can be judged based on a grain kernels that arises from the middle of the cob and was cut lengthwise. Table 10.4 presents different stages of ripening and the corresponding dry matter contents of the cob. 


Combine and determine the whole plant dry matter content
Table 7-9 below shows the whole plant dry matter content based on the conditions of the proportion of grain, dry matter content of the stover, and dry matter content of the cob.
(3) Harvest methods
Corn silage is usually harvested with self-propelled precision chop harvesters with a corn row- header or a row-independent corn header.  The advantage of row-independed headers is greater flexibility and harvest.
① Stubble height
The optimal stubble height varies between 10-15 cm and this is depending on the flatness of the plot. A shorter stubble height is not desirable because of the greater risk on contamination with soil. This lowers the nutritive value and it will damage the knives of the chop harvester.
Stubbles and stems have higher moisture content than the cob and are also less digestible. This makes it possible to influence the yield and the quality with the stubble height. With each additional 10 cm stubble heigth, the concentration of Net Energy for lactation (NEL) will increase with 0.6%. On the other hand, the dry matter yield decreases by approximately 2.5%. The overall nutritional yield decreases by approximately 2% per 10 cm stubble height. In general, increasing the stubble height is thus a fairly expensive method to increase the nutritive value.
② Chop size, theoretical length of cut
The optimal theoretical length of cut is between 6-8 mm. A larger theoretical length of cut does not contribute to a better supply effective fiber or dietary physical structure for the cow and it will influence intake negatively. A large chop size results also in more selection at the feed bunk and more refusals (stalks, leaves) and feeding losses.  Moreover, a larger chop size makes it more difficult to compact the silage pit resulting in a greater air penetration during feed out which may result in heating of the clamp and infection with aerobic organisms (fungi). Research by Wageningen UR Livestock Research has shown that a theoretical length of cut of 6 mm results in on average a 5 to 10% higher density (kg DM/m3) of the silage clamp when compared with a theoretical length of cut of 15mm.
Worn out of knives and poor adjustment of the knives blades give an irregular chop length. It is therefore best to check the chop size and chopping quality several times during the harvest. The length can be checked by measuring the length of a number of right-angled chopped stems. A poor chopping quality results in long ragged parts of dry stem and leaves.
Judge the theoretical length of cut during shredding
③ Grain processing
All grains should be damaged in such way that the pieces are no larger than a quarter of the grain in order to be utilized well by cows (see also the chapter Nutrition). To crush the grains, there are several options such processor rollers (cracker rollers), ribbed based panel beneath the reel or by placing rasp bars on the blades. Most of the self-propelled precision chop harvesters have a roller. It is mounted behind the chopper unit and consists of two counter-rotating knurled crushing rollers. The grains are crushed in between the processor rollers that turn around with different speeds. The structure of the other parts of plants is little affected by the crushing rollers. The distance between the two rollers is adjustable to control the intensity of crushing. To crush well, the grain kernels crusher is set at a minimum distance of 1 mm. Using a grain kernels crusher affects the capacity of the precision chop harvester. Since a grain kernels crusher uses around 7.5 kW per row extra, the total capacity will drop with a constant drive power. 

7.5.2.2 Storage 
The focus of this chapter is on the silaging process and silage losses. Heating, moulding, and some contaminations will be discussed as well. 
(1) Ensiling process
Ensiling requires anaerobic conditions for a lactic acid fermentation. Therefore, corn is sealed airtight using good quality plastic sheeting. A rapid development of lactic acid bacteria occurs during the first stage of silage fermentation. A rapid drop of the pH level silage reduces the growth of undesired clostridial bacteria. In corn silage, the of a stable silage is between 4.0 and 4.2. When the formation of lactic acid does not start up well, harmful bacteria can grow and they will result in a poor preservation of the silage that leads to substantial silage losses. Measures should be taken that to promote lactic acid bacteria and suppress the clostridial. 
① Ensiling corn silage
Corn silage will well preserve by:
•Sufficient sugar and lactic acid bacteria. Sugars become available for lactic acid bacteria when shredding. This results in a drop of pH from 4.0 to 4.2;
•Low protein and mineral levels. Proteins slow down acidification (buffer effect). Products with lots of protein like young grass are therefore difficult to conserve.
•Relatively low temperatures in autumn that cause butyric acid bacteria to be less active.
•Well-preserved corn silage contains little butyric acid and the NH3 fraction is low. The NH3 fraction is therefore not determined when analysing corn silage. 
With a good silage fermentation, there is a sufficient amount of lactic acid produced within two weeks after ensiling to create a stable silage. The amount of lactic acid is among others dependent on the dry matter content, but it is usually around the 2% (in the fresh product). 
It is important to seal the silage clamps within one after harvest. Otherwise, the temperature in the pit will rise as a result of air penetration. These aerobic conditions result in more acetic acid and less lactic acid which results in a less palatable feed and reduced intakes. 
It is preferred to keep silage closed for at least 4 weeks after ensiling. 
② Gas formation
Heavy gas formation sometimes occurs after sealing the corn silage. It may be necessary to tap when the plastic sheet becomes too bulb. This is usually caused by corn silage that is harvested too early (too wet, below 28% dry matter) because it contains relatively a lot of green plant parts and has relatively low dry matter content.  In addition, gas formation is triggered by heavy fertilization with nitrogen and heating. With less well preserved silage, extra carbon dioxide and hydrogen will develop, while nitrate (from the green plant parts) will be broken down into nitrate and other nitrogen compounds. This mixture of gas is yellow/brown and very toxic. With inhalation or skin contact it can damage the lungs and skin (burning).
If a strong gas development occurs in a silage clamp, then it is necessary to open the plastic sealing on both sides to let the gas escape. Shortly after removing gas, it is necessary to close the pit air-tight. Sometimes it is necessary to repeat everything. 
Silage pits with heavy gassing are no hazard to feeding livestock. The quality is also not or little affected. Side effects are discolouring to orange or brown. Gas formation can be prevented by normal fertilization of corn silage, harvesting at the right time, and careful silage making.
③ Ensiling losses
Silage losses in the clamp occur because of respiration of corn at the start of the conservation process and through conversion of carbohydrates and protein in organic acids and ammonia. In addition, wet corn silage (less than 32% dry matter content) can cause effluent losses. With a sufficient dry matter content of corn silage losses can occur because of limitations in conversions. There is a strong relation between the whole crop dry matter content at ensiling and ensiling losses
 (figure 7-10). Research from 2003 and 2004 from Wageningen UR showed no differences between “stay green” corn hybrids and “dry down” corn hybrids (figure 7-11). At the same whole crop dry matter content, “stay green” corn hybrids have a higher dry matter content of the grain and a lower dry matter content in the stem and leave fraction compared to “dry down” corn hybrids. In short: stay green hybrid have more a mature grain, with a larger proportion of green leaves, whereas dry down hybrids have a less mature grain and higher dry matter content in the leaf and stem fraction.
Ensiling losses occur as a result of the ensiling process as result of the conversion of carbohydrates in lactic acid. However, these losses are very limited with a good ensiling and preservation practice. 
If this is not the case, losses could rise significantly through heating, moulding, and putrefaction.
A distinction can be made between losses on dry matter content and losses on nutritive value net energy. Net energy losses (Net energy for lactation) are always higher compared to the dry matter content losses, especially in cases of humid corn. This is because the best digestible substances will be lost with the effluent during fermentation. 
From research on ensiling was shown that the effluent losses are different between stay green corn hybrid and dry down corn hybrids (figure 7-11). 
The threshold whole crop dry matter content to prevent effluent losses was 31% in dry down hybrids and 32.5 % in stay green hybrids. Also, more silage effluent losses occurred with stay green hybrids when the corn was ensiled at a low dry matter content. At 28% dry matter content, the amount of silage effluent was 14 and 25 litres per tonne for dry down hybrids and stay green hybrids, respectively. 
(2) Storage
① Dimensions of the silage bunkers
The dimensions silage clamps and bunker silos depend on minimum the feed out rate to prevent or minimize heating and moulding. To prevent heating and moulding feed out rate of 0.3 m per week is required. The preferred dimensions of the bunker silos can be calculated from feed demand per day (kg dry matter per day) and the density of silage (kg dry matter per m3) 
② Filling silage clamps and bunker silos
A number of aspects are important for easy and airtight sealing of silage clamps and bunker silos and to well and make use of the available space to get a well conserved product: 
•With bunker silos it is desired to place plastic sheets alongside the walls (figure 7-12) to get a good enclosure of the upper corners. 
•The silage clamps and bunkers be build up from thin layers of corn silage will result in the best compaction. Heavy wheel loaders or a heavy tractors needs to drive continuously to compact the silage. 
•Fill the silage clamp or bunker  in a short period (maximum 1 day) and take care of immediately airtight sealing of the silage. 
•The sides of clamp need to be sloping, 60 degrees for clamps without a sand load, 45 degrees sloping for clamps with a sand load. 
•In bunker silos it is important that the silage will be slightly higher on the sides compared to the middle, hence it needs to be stored in a hollow shape (figure 7-10). The sides will be more firmly compacted and the risks of damaging the walls and sheeting by the compacting vehicle are smaller.
•Silos need to be filled well and evenly until just above the walls to be able to make a good airtight and watertight enclosure.
•Clamps and silos need to have a smooth surface. In this way it is possible to stretch the plastic tightly and to promote the run off of rain water from the surface of the clamp.
•Ramps need be removed as much as possible. This saves space and plastic.

Silos are preferred for storing corn silage

(3) Covering and sealing of silage clamps and bunker silos
① Silage clamps and bunker silos with a sand or soil load
Using a sand load or soil load on top of the silage clamp or bunker has some advantages. First, sand load reduces air penetration en reduces the risks of heating during feed out. A sand load protects the silage against damage by birds and storm and wind. The soil on top on top of the silage should be fine and free from sharp stones and heavy clods which damage the plastic sheeting.   
When using a soil load, corn silage can best be covered with 0.15 mm thick polyethylene (PE) sheeting. The layer of soil can be about 10-15 cm. 
② Silage clamps and bunker silos without a sand or soil load
Sometimes it is not possible to cover a silage clamp or bunker silo with a sand or soil load. For example very high and wide bunker silos. In this situations it is necessary to put two layers of 0.15 mm thick PE sheeting on top of silage (figure 7-13). Both sheets need to be fixated with sand or sand bags on the sides. 
To protect the silage against dogs, cats, birds, hail, storm and wind, it is possible to add another protection sail on top of the PE foils. It is important that the foils remain tight on top of the silage and that it is checked whether there are damages or not. An option is to use sand bags or plastic band (with sand bags or straps attached to the silo walls) to reduce the impact of wind.
(4) Density (m3 weight)
The density (expressed in kg dry matter content per m3) can vary in the corn silage. This is dependent on the stack height, soil or sand load, dry matter content, theoretical length of cut, and degree of pressing. Table 7-10 shows the m3 weights of corn silage for various situations. The density is given as an average of the whole clamp. Within the silage clamp the density may vary. In the middle on the bottom, density will be higher compared to the top and sides. 
(5) Heating and moulding
Heating and moulding easily develop in corn silage. Heating and moulding is caused by penetration of air in the corn silage during conservation and feed out. Various bacteria and moulds will become active under aerobic conditions and start to grow. This results in loss of nutrients and heat production. The losses increase when heating endures or when temperature increases. Losses can increase up to 2-3% of net energy for lactation per day. Another side effect is that the product will be less palatable resulting in a reduced intake. 
Prevention of heating and moulding during feed-out 
•Prevent air penetration during feed-out. For silage clamps and bunker silos without a sand load, use sand bag to prevent penetration or air between the top of the clamp and the plastic sheeting
•During feed out is necessary to maintain a smooth and undisturbed silage face.
•Use heat inhibitors (propionic acis) or special mixtures with heterofermentive lactic acid bacteria. These compounds inhibit the activity of micro-organisms. This riks on heating can be diminished by adding these mixtures on top of the silage clamps before closure. However, adding propionic acid and heterofermentive lactic acid bacteria with special equipment on the chop harvesters is more effective. 
(6) Moulds
Usually, moulding starts at the outside of the pit because of air flow. Sometimes there are moulds with striking colours in the middle of a well-conserved pit. These are the moulds Penicillium roqueforti, Monascus ruber, and Chrysonilia sitophila. 
① Penicillium roqueforti
The Penicillium roqueforti shapes blue-green bulbs that have a diameter of 10-20 cm. These mould bulbs usually exist in the upper part (low density) of the pit, but not in the outer layer from 0-15 cm because it is too cold. This mould can grow almost without oxygen and it can produce toxins. In practice, these toxins are rare. Not everything is known about the growth conditions of this mould. It does appear that this mild usually exists in pits that have a low feed out rate. Moulding results in a less tasteful product with lower nutritive value. Therefore, it is advised to take the blue-green mild bulbs out of the pit and to not feed them. A well compacted, airtight pit and a sufficient feed out rate can diminish or even prevent the growth of such moulds. 
② Monascus ruber
The Monascus ruber shapes red-purple bulbs in the corn silage. This mould grows under the same conditions as the blue-green mould. The Monascus produces almost no toxins and is not harmful. Still we advise to take out the mould bulbs, but first make sure that the corn silage is conserved well and that the feeding speed is sufficient. 

Chrysonilia sitophila
The Chrysonilia sitophila is an orange mould that usually exists in the face of the clamps of heating corn silage. The mould grows with higher temperatures (25-30 C) and can grow very fast in a couple of days only. This explosive growth leads to extra heating and a quick decline in quality (putrefaction). This mould is not toxic.


Some moulds have striking colours, like the Monascus ruber

(7) Mycotoxins
Mycotoxins are produced by moulds. A distinction is made between field moulds and storage moulds. The presence of moulds is dependent on the conditions. Field moulds are mainly affected by the weather (humidity and temperature), soil functioning, fertilization, and crop rotation. Storage moulds are mainly affected by temperature, humidity, time, and conservation. Hundreds of mycotoxins are known. From the mycotoxins that are relevant to dairy cattle, deoxynivalenol (DON), zearalenon (ZEA), and roquefortin C occur most often. DON exists mainly in grains and corn. ZEA exists mainly in corn, grasses, and a variety of feed ingredients. Both mycotoxins are produced by fusarium moulds during cultivation of the crop (field moulds) and they remain stable in the silage. Corn silage is commonly part of the ration of dairy cows and is together with grass and corn an important source of DON and ZEA Roquefortine C is produced by Penicillium roqueforti during the storage time (storage mould). The transmission of these mycotoxins from feed to milk is low (0.03% or lower).
Little is known about the metabolism and toxicity of mycotoxins in dairy cattle. DON is to a large extent degraded in the rumen. Hence, no clinical effects on the health of dairy cows or negative effects on the feed intake and milk production are expected.. ZEA is not or barely degraded in the rumen. When there is a high amount of ZEA in the feed it is not unlikely that it will have a negative effect on fertility.  There is insufficient knowledge on the effect of roquefortin C on dairy cows. Table 7-11 shows the standards for DON and ZEA in a ration for cattle in the Netherlands. The amount that can be in a singular feedstuff is among others determined by the amounts of remainder products in the ration. The “ Productschap Diervoeder (PDV)” determined in 2004 that for singular feedstuffs 3x the standard can be followed for a ration (Qualityserie nr 96). 
Control of DON and ZEA (and other field moulds) can be done through cultivation management, like plowing or removing stubble remainders. It is however not shown that corn varieties with a high fusarium resistance contribute to low amounts of DON and ZEA in the feed. Control of roquefortin C is possible through taking into account the silaging method and through feed management.

7.5.2.3 Nutrition
Corn silage is major part of cattle diets. Compared to other forages,corn silage has a high nutritive value, is an important source of starch and has compared to other  as a forage crop is among others due to the high and constant nutritive value (VEM). Corn silage also fits well in a dairy cattle ration that contains grassland products . 
(1) Nutritive value
Digestible organic matter contributes to the nutritive value of roughage as it consists of structural and non-structural carbohydrates, fats and proteins. Nutrients are released when digestible organic compounds are digested in the rumen and intestines and these are used for the formation of milk constituents and the formation of body reserves. (Table 7-12).
(2) Analysis of nutritive value
In order to formulate adequate cattle diets it is important to sample and analyse corn silage for chemical composition and nutritive value. 
① Structural carbohydrates
Carbohydrates from corn silage are by far the biggest suppliers of net energy  to cattle . Carbohydrates can be distinguished into structural carbohydrates and non-structural carbohydrates. Structural carbohydrates mainly stem from cell wall compounds that contribute to the firmness of the plant. In a good developed crop harvested between 28 and 35% dry matter in the whole crop, cell walls contribute to approximately 40% of the digestible organic matter. Structural carbohydrates that contribute most to energy supply are cellulose, hemi-cellulose, and pectin.  Non-structural carbohydrates are composed of starch, sugars, and fructosamines. The most important structural carbohydrates in corn silage are cellulose and hemi-cellulose that come from the leaves and stems. A large part of the cellulose and hemi-cellulose is digested in the rumen and part will leave the cow undigested. Degradation of cellulose and hemi-cellulose in the rumen mainly results in acetic acid which is absorbed in the blood through the rumen wall. Acetic acid is used for the synthesis of milk fat. 
The crude fibre content and the content of the cell wall fractions (NDF, ADF, ADL) are measures for content of structural carbohydrates.  The crude fibre content gives an indication on the amount of cell walls without distinguishing between different cell wall fractions. The cell wall fractions NDF, ADF, and ADL give insight on the type ture and relationships between cellulose, hemicellulose, and lignin (table 7-13).  
② Non-structural carbohydrates
The most important non-structural carbohydrate in corn silage is starch which is stored in the grain. The starch content varies and is dependent on the hybrid and stage of maturity at harvest. The starch content can vary between 250 and 400 grams’ starch per kg dry matter in a normal developed crop of corn silage that is in between 28 and 35% of dry matter content. The non-structural carbohydrates can be categorized in various fractions based on the rate digestion site of digestion in gastrointestinal tract GI-tract. 
The first, category are sugars and readily rumen degradable starch (S+RRDS). These sugars and starches are degraded in the rumen at a rate of at least 12.5% per hour.
The second category is slowly rumen degradable starch (SRDS), which degraded in the rumen to propionic acid. The third category is rumen by-pass starch (RBS) which passes the rumen. Rumen by-pass starch is degraded in the small intestine in to glucose. 
Compared to other starchy feeds, starch from corn silage is relatively slowly degraded in the rumen  (table 7-14). Approximately 65 to 80% of starch from corn silage is slowly rumen degradable starch (SRDS) which degraded in the rumen; about 20 to 35% of the starch is rumen by-pass starch (RBS) and passes the rumen undegraded. The proportion of readily rumen degradable starch (S+RRDS) usually very small (<2%). 
③ Protein
Corn silage is high in energy but relatively low in crude protein and digestible protein available in the intestine (DPI). Because corn silage is high in energy and low in protein the rumen degradable protein (RDP-balance) is negative, which means that rumen degradable protein is limiting for growth of the rumen microbes. 

Corn silage mainly has a high nutritive value due to high starch content.
The DPI is the amount of rumen by-pass feed protein and microbial protein synthesized in the rumen Microbial protein synthesis requires an energy source which the organic matter fermented in the rumen and a nitrogen source which is mainly ammonia that is released in the rumen with the degradation of rumen degradable feed protein, dietary non-protein nitrogen and urea that enters the rumen with saliva. The latter originates from ammonia that absorbed in the blood through the rumen wall and converted to urea in the liver. Urea is partly excreted in milk and urine but is also returned to the rumen via saliva. The energy source that is necessary for formation of microbial protein comes from the fermented organic materials. With corn silage, these consist out of digestible cell wall fractions and rumen degradable starch. Corn silage has a negative RDP-balance. A shortage of nitrogen (indicated by a negative RDP-balance) may limit organic matter fermentation in the rumen. For a good rumen function, maize silage based diets needs to be supplemented with protein sources which provide sufficient amounts of rumen degradable protein (e.g. soy bean meal, canola meal, alfalfa haylage)
④ Fat 
Triglycerides and fatty acids that can be used for the formation of milk fat originate during the degradation of fat in the rumen and intestine. Corn silage contains only 3 to 4% fat.  Fat from corn silage is therefore only contributing a little to formation of milk constituents. 
⑤ Minerals trace elements, and vitamins
Minerals and trace elements play an essential role as functional groups in enzymes and antibodies and biochemical processes, e.g. in development of the skeleton, transport of ions through cell membranes, body fluids, and in the nerve functioning. The concentrations of minerals in corn silage are low. Therefore, corn silage based diets needs to be supplemented with minerals and trace element.
With adding minerals and trace elements to a dairy cow ration it is necessary to consider that both an shortage and excess of minerals and trace elements can be harmful to the animal. 
Vitamin deficiencies are rarely a problem in ruminants. A large amount of vitamins are produced in the rumen of ruminants, especially the vitamin B-complex, vitamin C, and K. Fat solvable vitamins A,D, and E are most essential for ruminants. Plant based feed contains no vitamin A.  Plants do contain the pro-vitamin ß-carotene which is converted to vitamin A in the gastrointestinal tract. Vitamin D demand is dependent on the calcium and phosphor metabolism. Vitamin D can be synthesized by the animal itself in presence of UV-light. 
Standard premixes that contain minerals, trace elements, and vitamin A, D, and E are usually added to a TMR. However, it is necessary to pay some special attention to appropriate mixing and distribution of the minerals, trace elements, and vitamin through the TMR. 
⑥ Effective fiber, dietary physical structure
Dairy cows need sufficient structure in the ration of dairy cows to be able to ruminate and to stimulate rumen motility. Rumination stimulates saliva production. Sodium bicarbonate in saliva buffers the rumen pH. A rumen pH above 5.8 is required for a good rumen fermentation and fiber degradartion. 
The physical structure value (or effective fiber) of corn silage is related to the cell wall content (NDF and crude fiber) and to a lesser extent to the theoretical length of cut (chop size). A higher cell wall content and larger chop size results in more effective fiber and dietary physical structure. 
An increase of theoretical length of cut with 1 mm results in a 2% higher dietary physical structure with only marginal effects on rumen pH. Therefore, it is not recommended to increase the theoretical length of cut (chop size) to provide more effective fiber. Although, research showed that a greater theoretical length of cut (>9mm) resulted in more rumination activity per kg dry matter and per kg NDF, total chewing time (eating plus ruminating) did not change because a shift between eating activity towards ruminating activity. Moreover, a greater theoretical length of cut (chop size) resulted in a reduced dry matter intake, and more feed selection by the cows. More selection at the feed bunk resulted more feed waste and a lower feed utilization. A larger theoretical length of cut resulted in an improved fiber digestion, but in a reduced digestibility of the grain fraction. Ultimately a larger theoretical length of cut resulted in a reduced dry matter digestibility. As pointed out earlier, a larger theoretical length of cut resulted in a less dense packing of the silage clamps and hence a greater risk on air penetration and heating.