Forage Quality

Nov 22, 2021

It’s common knowledge that forage provides relatively low-cost nutrition to livestock. For ruminant, equine & other herbivores, forage is essential and must be of good quality since producing and properly preserving quality forages aid in animal performance while potentially reducing costs associated with feeding.  Having the best possible forage for dairy cattle can ultimately save large amounts of ration costs.  Forage quality, however, is a somewhat complex term and deserves greater respect and attention.  Forage quality in short relates to digestibility and, when digested, how the animal utilizes the nutrients obtained.  Whether harvesting and preserving forage as silage, baled hay, green-chop or pasture, consider these factors in determining the potential for producing the most optimum quality & digestible forage possible:
Plant maturity - Development of the plant is probably the biggest influencing factor affecting forage quality. Remember, forage is persistently growing and change will take place as the plant matures.  As the plant grows, lignin will accumulate and will have negative effects on digestibility.  It is possible that as the forage matures, digestibility can decline every two or three days.  Thus, an extended delay in harvesting can have paramount impact of forage quality.
Environment - Rainfall, temperature, and the amount of sunlight directly impacts forage quality. Moisture damage is harmful to forage quality. If inclement weather delays harvesting allowing the crop to become more mature, expect lower forage quality. Also, higher temperatures will increase lignin accumulation and lower digestibility.
Managing Corn Silage:
The value of silage, particularly corn silage is well established due to the higher yield of nutrients per acre of land, general increase in forage quality, less harvest losses & potential lowered feed costs.  In order to capitalize on the investment of harvesting the crop, it is essential to manage the silo & ensure highest quality forage for the cow.  It is important to point out that silage is a vibrant feedstuff in that a delicate balance of microbial action based on absence of oxygen, carbohydrates for energy & the eventual acidity of the crop must be met to produce good, digestible forage.  Slight changes in the above conditions can very quickly affect the nutritional value.  In our area, spoilage, generally from exposure to oxygen, plays a large role in limiting silage quality.
Anaerobic (absence of oxygen) condition & low pH prevents activity of microbial organisms responsible for spoilage.  Exposure to small amounts of oxygen can facilitate yeast growth which converts plant sugars to waste material.  This results in pH rise allowing other bacteria & molds to expand instead of being controlled by a more acidic environment.  Thus, forage quality is reduced due to losses of digestibility & energy while increasing temperature & potential presence of mold.
Silage smell & color are good indicators of quality of silage, however, it is very useful to obtain forage assay to determine dry matter (DM), pH & fermentation acid profile.  “Normal” silage that has undergone optimal fermentation has light green to green-brown color with slightly sweet smell of lactic acid.  Putrid, rancid odors with darker brown color & slimy texture typically are present when clostridial fermentation has occurred.  Moisture content at harvest can play a large role on forage quality.  It is well known that drier silage reduces overall DM digestibility, reduces feed intake & typically results in lower quality material.  However, too wet can alter fermentation producing low pH (more acid) & potentially reducing sugar content. 
Silage feeding from storage should not occur until the fermentation process is complete.  Opening the silo before stability of silage material results in dairy cow digestive upsets & lowered milk production. The full fermentation phase generally takes between two and three weeks to stabilize the silage.
It is very important to control spoilage of the exposed face of the silo.  Hopefully the design of the silo prevents the face from exposure to prevailing winds & hot, direct afternoon sunlight.  Since the silo face is constantly exposed to air, the removal rate must be enough to prevent aerobic spoilage.  Minimize the exposed surface area by removing silage evenly for the entire face forming a smooth, vertical surface perpendicular to the side of the silo & floor.  Scrap from the top down if utilizing front-end loader.  Lifting from the bottom can create cracks allowing air to penetrate deep into the silage. 
Silage spoilage can also occur at the feed bunk.  Ensure that silage is fresh in the bunk by removing refused feed.  Good feed bunk management includes multiple feedings per day & limiting feed mixing too far ahead of time before offering to the cow.  During warmer months, it is sometimes beneficial to include a mold inhibitor to prevent excess TMR warming & unwanted mold growth.  Additionally, it is advantageous to “push-up” the TMR several times daily if utilizing a flat bunk feeding area.  Remember, encouraging & promoting feed intake is vital for maintaining a profitable milking herd.
It is important to evaluate all of these factors in determining silage quality & for ration balancing purposes.  The key to maximizing milk production & profitability is providing the best possible & palatable ration. 
How can forage quality be determined?  Generally, forages are evaluated physically (visually) and chemically (lab assay).  Use of both methods is important.  The following is a general guide to important points in determining quality:
Physical Appearance:
Stage of maturity – examine for presence of seed heads/flowers/seed pods.  These can indicate greater maturity of the plant at harvesting.
Color – while color is not a good indicator of nutrient content, a brighter green color would suggest minimal oxidation or sun bleaching.  This could affect vitamin content.
Leaf: Stem ratio – determine whether stems or leaves are more obvious.  Higher quality forages have greater proportion of leaves while stems will be less obvious.
Foreign objects – look for presences of mold/weeds/poisonous plants.  Also, notice other objects such as wire.
            Smell – quality forages will have a fresh aroma without musty/moldy odors
            Touch – note the stiffness of the forage.  Hays should have fine, pliable stem
Regardless of the physical/visual evaluations, always have forages tested in order to provide the best possible rations.  Evaluate total forage needs/requirements and select the crop, variety and the appropriate acreage of that crop that best meet the needs of the group or groups of animals to be fed. It ultimately comes down to economics; better quality forage produces greater responses for the animal.  Contact local feed and animal health specialists at your local Co-op to aid in determining forage needs and quality.

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