11/14/2019
The Problem with Corn Silage Feeding Trials
Shared from Inside the ZONE® newsletter, Pioneer Nutritional Sciences
When wanting to verify or quantify that a management practice, hybrid, inoculant, or piece of machinery improves silage quality, conducting a feeding trial sounds like a great idea. Why not compare the performance of cows fed corn silages with and without the practice or product of interest.
Any feeding trial is complicated and fraught with sources of error, but evaluating corn silage quality characteristics adds confounding dynamics that are commonly overlooked. Uncontrollable variables in corn silage production alter multiple quality metrics making feeding comparisons typically unreliable and ineffective at discerning the desired attributes.
Corn Silage Quality is Complicated
The definition of corn silage quality varies and is far from simple. An incomplete list of often cited contributing parameters includes percent dry matter, starch content, starch digestibility, fiber digestibility, sugar content, and palatability. Unfortunately, these nutritional characteristics are largely independent factors. In other words, it is impossible to alter one quality metric for comparison without other, non-target quality parameters also changing.
Producing Comparable Corn Silages
To execute a feeding trial, an adequate volume of each kind of silage must be produced to feed a group of animals for a predetermined period of time. Numerous acres are required to produce enough of each silage corn. It is impossible to grow both treatments on the exact same acre. For this reason, independent influencers of corn silage quality related to micro-growing environments will confound the ability to run a well-controlled comparison.
Natural Variation in Quality
Nearly all quality attributes can change significantly with only subtle changes in growing environment. A single hybrid with the same planting and harvest dates will demonstrate large variation in quality metrics within the same relatively uniform field (Figure 1). Even if the goal was two silages of identical quality the likely result would be silages with impactful feed values differences. Natural quality variation alone is enough to alter animal performance.
Quality Variation within a Single Field
Figure 1: Quality analyses of representative samples from 8 random loads of 155 acre field, 93% by area one soil type, one hybrid, one planting date, one harvest date. (Pioneer, Ohio, 2016)
Example of Practical Application
It is often claimed that a certain corn hybrid product or brand is superior in quality due to it possessing a particular natural or genetically modified characteristic. Frequently cited are cow responses of increased milk production upon switching cows onto silage containing the particular product attribute. However, what other factors may have caused the milk response? For instance, if the claim is higher starch digestibility, increased milk output may have actually been due to higher starch content, higher fiber digestibility, or another independent quality metric unrelated to the claim.
Ask questions of corn silage quality attribute feeding trials:
- Were the two corn silages grown in identical growing environments? (e.g. field, soils, plant/harvest dates, agronomic practices)
- Were all non-target quality parameters identical? (e.g. dry matter content, starch content, fiber digestibility, kernel processing, length of cut, fermentation profile)
- Were comparison groups fed identical diets? (e.g. haylage of identical quality, TMR NDF content)
- Was the environment of the cattle identical for both treatments? (e.g. weather, ventilation, cow comfort, lighting, stocking density)
- Were the cattle the same for both treatments? (e.g. pre-trial diet, pre-trial milk production, days in milk, reproductive status, parity)
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