Cattle, especially lactating dairy cows, require a high quality, energy dense feed. Corn silage is especially popular for this purpose and is used by farmers across the country as a year round source of forage. Not all silage is created equal however, and to determine how your silage stacks up in terms of nutrient quality, it's necessary to look at the feed values.
Representative samples are sent in to a lab to accurately evaluate the silage components. There are a lot of factors that can be tested for, so let's briefly cover a few of the most important tests and how exactly they are determined:
1) Acid detergent fiber (ADF) and neutral detergent fiber (NDF) readings help to predict the overall energy content by measuring the percentage of fiber in the silage. Lower levels are desirable as animals will fill up faster on a high-fiber diet, resulting in lesser amounts of feed consumed and less available energy. ADF levels below 26% and NDF levels below 50% are desirable.
2) Lignin is one of the fibers that makes up ADF and NDF totals. It is often tested for additionally because not only is it indigestible, but it also restricts the absorption of other digestible fibers. A lignin value below 4% is desirable.
3) Crude protein levels give a basic overview of one important form of available energy. The higher the percentage the better, with averages falling between 6% and 8%. Protein is also important for supporting a healthy intestinal microbiome in ruminants (such as cattle).
4) Starch is an important factor to look at as it provides 75% of the digestible energy found in the corn kernels and 45% of the overall silage energy level. The amount of starch in silage is directly proportional to the amount of grain present. Starch levels tend to increase with the size and number of ears.
All of these feed values are dependent on a long list of factors: moisture level, maturity and height of corn at chopping, processing and fermentation practices, laboratory testing approaches, and of course just the general genetic predisposition of that variety.
Figure 1: A variety of feed values across various cutting heights for corn.
Figure 2: The proportion of nutrient loss in relation to moisture levels during ensiling.
In the previous post titled "How the planting rate of corn affects the production outcome", we discussed the fine line between planting density and the resulting silage yield/quality. From a feed value standpoint, planting at a lower density may be more desirable. While this requires a potential trade off with yield, it can increase the proportion of valuable nutrients with larger, more well-developed ears. Reducing competition increases available nutrient uptake, including greater access to sunlight and pollination. It only makes sense then that values such as starch and protein percentages will increase in silage that was planted at a lighter rate.
Harvest time is the next major milestone in establishing good quality silage. Figure 1 on the top left shows that raising the height of the harvester might reduce yield slightly, but it increases the overall nutritional value since larger pieces make more of the good fiber and proteins available by retaining original structure. Figure 2 on the bottom left demonstrates how ensiling at a higher moisture content prevents the loss of valuable nutrients (denoted here as "effluent").
Figure 3: The balancing act between corn maturity and amount of energy available.
Another important growth factor besides initial planting density that determines silage quality is the corn's maturity at harvest. Figure 3 demonstrates the increase in available energy content up to a certain maturity level. The decline is due to reduced digestibility of plant matter and kernels over an extended period of time.
Getting an accurate nutrient reading by a trusted laboratory is the last step in giving you the numbers you need. Collecting a good, representative sample and shipping it as fresh as possible (or freezing to preserve quality if not shipping immediately) will help maintain accurateness. Be aware of what values to have tested and how the results will impact your feeding management plans as you start to incorporate that silage into the diet.
Baglietto Seeds makes sure to thoroughly test all of our corn varieties over multiple years and locations to get a wide range of data across different environments. Silage samples from our plots are extensively tested for feed quality and many of the factors discussed in this post. The results of such tests can be found under each respective corn variety.
As you can see there is a lot more to the value of corn silage than meets the eye, and frankly too much to cover in a single post. If you grow or plan on growing corn for silage, it is crucial to be aware of all the factors that might play a role in determining its ultimate feed value. Management of good feed starts before seed goes in the ground and continues until it is chopped, ensiled and stored.
References:
"Quality and Feeding", Corn Agronomy, University of Wisconsin, http://corn.agronomy.wisc.edu/Silage/S006.aspx
"Estimating the Energy Value of Corn Silage and other Forages", P.H. Robinson, University of California, Davis http://alfalfa.ucdavis.edu/+symposium/proceedings/2001/01-189.pdf
"Impact of Starch Content and Digestibility in Dairy Cattle Diets" Luiz, Ferraretto, University of Florida, http://dairy.ifas.ufl.edu/rns/2017/Ferraretto.pdf
"Quality of Corn Silage", Bitman, Shabtai, Advanced Silage Corn Management, http://www.farmwest.com/book/export/html/843
Figure 1: Pioneer Hi-Bred International, "Dairy Herd Management", June 2000
Figure 2: "Effect of moisture content on corn silage effluent", S.C. Fransen, Washington State University
Figures 3: "Processing Corn Silage", J. Harrison and L. Van Wieringen, Department of Animal Sciences, Washington State University