Forage Quality

Oct 04, 2022

Producing and properly preserving quality forages aid in animal performance while potentially reducing costs associated with feeding. Forage quality, however, is a somewhat complex term and deserves greater respect and attention than is typically given. In short, forage quality relates to digestibility and how, when digested, 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 and digestibility possible:
Plant maturity:
The development of the plant is probably the biggest influencing factor affecting forage quality. As the plant grows, lignin will accumulate, causing 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 a paramount impact on forage quality.

Rainfall, temperature, and the amount of sunlight directly impact 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, the general increase in forage quality, fewer harvest losses, and potentially lower feed costs. In order to capitalize on the investment of harvesting the crop, it is essential to manage the silo and ensure the highest quality forage for the cow. It is important to note that silage is a vibrant feedstuff, meaning that a delicate balance of microbial action based on the absence of oxygen, carbohydrates, and the eventual acidity of the crop must be met to produce high-quality forage. Even slight changes in the above conditions can 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) conditions and low pH levels prevent the 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 a rise in pH levels, allowing other bacteria and molds to expand instead of being controlled by a more acidic environment. Thus, forage quality is reduced due to losses of digestibility and energy while increasing temperature and the potential presence of mold.

Silage smell and color are good indicators of the quality of silage; however, it is very useful to obtain a forage assay to determine dry matter (DM), pH, and fermentation acid profile. “Normal” silage that has undergone optimal fermentation has a light green to green-brown color with a slightly sweet smell of lactic acid. Putrid, rancid odors with a darker brown color and slimy texture typically are present when clostridial fermentation has occurred. The moisture content at harvest can play a large role in forage quality. Drier silage reduces overall DM digestibility, reduces feed intake, and typically results in lower quality material. However, too much moisture can alter fermentation, producing low pH (more acid) and potentially reducing sugar content. 
Silage feeding from storage should not occur until the fermentation process is complete. Opening the silo before the stability of silage material results in dairy cow digestive upsets and 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. The design of the silo should prevent the face from exposure to prevailing winds and 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 and floor. Scrap from the top down if utilizing a 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 and 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 and unwanted mold growth. Additionally, it is advantageous to “push-up” the TMR several times per day if utilizing a flat bunk feeding area. Remember, encouraging and promoting feed intake is vital for maintaining a profitable milking herd. It is therefore important to evaluate all these factors in determining silage quality and for ration balancing purposes. The key to maximizing milk production and profitability is providing the best possible and palatable ration. 
How can forage quality be determined? Generally, forages are evaluated physically (visually) and chemically (lab assay). The 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 the 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, which could affect vitamin content.
Leaf: Stem ratio – determine whether stems or leaves are more obvious. Higher quality forages have a greater proportion of leaves, while stems will be less obvious.
Foreign objects – look for the presence of mold, weeds, poisonous plants, or other objects such as wire.
Smell – quality forages will have a fresh aroma without musty/moldy odors.
Touch – note the stiffness of the forage. Hay should have a fine, pliable stem.
Regardless of the physical and visual evaluations, always have forages tested to provide the best possible rations. Evaluate total forage needs/requirements and select the crop, variety, and appropriate acreage of that crop that best meets 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. 

Your local Co-op is a great resource for all things animal nutrition. Find more content like this in this month’s issue of The Cooperator.

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