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By Mark Bowman and Amy Sova 
Ruminant Nutritionists, 
Grand Valley Fortifiers

With winter underway and harvest complete, now is the time to assess quality of corn silage and hay crops. These forages will be an essential component of winter feeding programs and dictate the extent of grain supplementation that is needed to achieve expected growth levels. Forages can vary greatly in quality due to weather, forage variety and harvest conditions. Sampling of these feeds can help us assess forage quality and plan when and where to use these feeds to meet performance goals. Our ration balancing philosophy is to maximize forage content of rations in order to minimize purchased feeds while meeting your goals. Fortunately, we have the software and laboratory feed analyses to help assess how feeds will perform on farm to help you to reach those goals.

Forages are the base of the ration and supply a large amount of digestible energy and protein as well as essential fibre to maintain rumen function. The quality of forage largely dictates how much forage cattle can consume and how much concentrate we will need to supplement. Neutral detergent fibre (aNDFom) is easily measured by labs and is the basic predictor of forage intake. NDF is a measure of plant cell wall components and consists of cellulose, hemicellulose and lignin. NDF is dependent on plant species and maturity. Lignin is indigestible in the rumen and increases as the plant matures. This results in reduced digestibility and energy content of the feed with increasing maturity. Total digestible nutrient (TDN) is a calculated lab value on your forage assay that reflects the energy value of feed and is a good comparison tool when evaluating your on farm feeds. For example, dry corn has a TDN value of 87% and corn silage has an average TDN of 71%. Supplementing dry corn is an effective way to add energy to a diet to meet maintenance and gain requirements if your animals are not maintaining condition or achieving the growth you are looking for.

More recently, we have been measuring NDF digestibility (NDFD) as a better predictor of forage intake potential. Lab analysis measures NDFD at three time points- 30hr, 120hr and 240hr which is the portion of NDF that is digested at those different time points in the rumen. The 30hr NDFD is the “fast” pool of fibre and the 240hr NDFD is the indigestible NDF portion. Ultimately, the indigestible fibre pool is the limit to how much forage cattle can eat. Feeding forages with lower NDFD 240hr will limit forage intake and performance if we don’t supplement more grain. Using dry corn to replace forages with poor digestibility may be needed to achieve desired weight gain or maintain condition of animals.

Table 1 reports the average NDF, TDN and forage digestibility characteristics for forages sampled by Grand Valley Fortifiers. As you can see, corn silage has lower NDF values and has higher NDFD than haylages. Within the haylage category, grassier haylages contain higher NDF content than alfalfa haylages but are also more digestible than alfalfa haylages.

Table 1. Grand Valley Fortifier Averages

Corn Silage









TDN (%) 71 64 63 63
aNDFom(%) 39.3 38.7 44.9 49.8
NDFDom 30hr (% of NDF) 55 46 50.2 54.3
NDFDom 120hr (% of NDF) 73 51.9 55.5 61.0
NDFDom 240hr (% of NDF) 78 55.9 59.2 65.1


So far this year, we are seeing lower quality corn silage in terms of starch level, TDN and digestibility. Dairy One summarized fresh corn silage data from the Northeast and found a general decrease in corn silage quality compared to 2016. In Ontario we can expect to see similar results due to similar geography and growing conditions. Wet weather, delayed planting and lower heat units may have played a role in the observed decrease in corn silage quality this year.

Overall, ADF and aNDF were 2.8 and 3.9 units higher this year (25.1 vs 22.3 and 43.9 vs 40.0%, respectively). Starch level was 3.5 units lower on average than last year (32.2 vs 35.7 %). In addition to lower energy value this year, we are dealing with lower NDF digestibility. The 30-hour NDF digestibility for 2017 corn silage was 6.7 units lower on average (53.2 vs 59.9%). This means that forage intake potential on new crop corn silage will likely be lower. In combination, the increased fibre levels and decreased starch and NDF digestibility levels results in the need to supplement more energy to cattle this winter to meet our performance goals. For example, if your winter ration typically doesn’t include much grain, this year may see a change in the amount of grain needed for nursing cows and growing feedlot cattle or replacement heifers. However, the extent of reduction in corn silage quality will vary by farm and region and not all farms will suffer from lower corn silage quality. Test your corn silage to assess fibre, starch and fibre digestibility levels so that the appropriate adjustments can be made.

A Closer Look at Corn Silage

High quality corn silage has high intake potential and energy content, requiring only supplementation of protein, minerals and vitamins to achieve high daily gains in growing feedlot cattle. For example, 800 lb steers could eat 44 lbs of corn silage and 4 lbs of protein and mineral/vitamin premix ingredients and achieve 3 to 4 lbs average daily gains depending on the type of cattle and management. Therefore, consideration needs to be given to corn silage quality when selecting seed corn hybrids for the next year.

Corn silage hybrids should be chosen with the goal of maximizing beef production per acre for maximum profitability. This requires selection of hybrids that will achieve both high yield per acre and that have high starch content and NDF digestibility, which will result in high beef production per tonne of silage. Corn silage feeding value for dairy cattle is reported as milk per tonne of silage dry matter, which is calculated from silage quality as described above, and as milk per acre, which multiplies the milk per tonne by the yield per acre. These assessments of silage quality and yield also apply directly to beef production. Therefore, chose a corn silage hybrid that is at least average or higher for yield per acre, starch content and NDF digestibility.

Other important criteria for corn hybrid selection include heat units required for maturity and agronomic traits such as disease and pest resistance, drought tolerance and susceptibility to molds and mycotoxins. Some of these traits will be specific to your area and others will apply most everywhere. Ask your seed company representative for data and recommendations on these characteristics and consider this along with your own experience on your farm.

Mycotoxins are often overlooked, but are very prevalent in the corn crop most years and can impair cattle performance and health if present at high levels. Symptoms include reduced or erratic feed intake, loose manure, poor hair coat and general dullness, lack of thrift and increased disease as mycotoxins challenge the immune system. Reduced average daily gain will result in growing cattle and reproduction may be impaired in heifers and cows. Therefore, if your cattle are showing these symptoms don’t overlook mycotoxins as a possible cause and investigate potential solutions with your Grand Valley Fortifiers representative.

This article was written for the Winter 2018 Beef Grist. To read the whole Beef Grist, click the button below.