Feedback: Current silage testing methods biased against leafy hybrids

To the Editor:

I am the breeder of the "leafy" and "leafy floury" hybrids being sold as corn silage specific seed. The article, titled "Corn Silage 2015: Now"s the time to plan for next year"s crop" (December 2014 edition of Dairy Herd Management), quotes Ev Thomas, Oak Point Agronomics, cautioning corn silage growers that leafy and leafy floury hybrids have "not yet produced a consistent advantage in NDF digestibility." Randy Shaver, University of Wisconsin-Madison dairy nutritionist, states that leafy and leafy floury hybrids had "lower NDF digestibility."

My response is: Compared to what? While their statements are true when comparing leafies to brown midribs (BMRs), this is not the case when comparing leafies to dual-purpose hybrids, which occupy about 70% of the corn silage market. The suggestion that BMR is a superior silage hybrid type is somewhat academic, given that the successful growing of a BMR crop is often fraught with difficulty.

One must remember that NDFd is but one criteria to be considered when selecting silage corn. Leafies have demonstrated dependably high yields that are achieved at lower plant populations, high total plant digestibility (including high starch digestibility), and a wide harvest window that results from slow kernel drydown matched with moderate plant drydown. Leafies can also be fed after only 30 days in the bunker.

The article also suggested that one should look to local and regional trial data (which includes quality testing) when selecting silage hybrids. However, leafies are not widely entered into these trials because standard testing methods are geared towards assessing dual-purpose and BMR hybrids rather than leafies. As such, the test results do not accurately reflect the unique benefits of leafies.

Here are three reasons why leafies are not entered into state trials:

 1) A leafy plant needs more space in the corn canopy because it is larger than that of bmr and dual purpose grain hybrids. State trials are conducted at about 35,000 ppa. Leafies at that population produce silage having less starch and lower NDFd than if planted at the recommended 28,000 to 30,000 ppa.

2) The quality tests performed in conjunction with the state trials attempt to provide a measurement of total starch content through Near Infra-Red (NIR) testing. However the NIR formulas used to determine starch content in a sample have been calibrated mostly using dual purpose corn which has a higher concentration of vitreous starch. The result is that these tests estimate the presence of vitreous starch in the samples but inaccurately estimate the presence of floury starch which is abundant in Leafies and Leafy Flouries.

3) Not only is the total starch content for leafies inaccurately reported by NIR testing in state trials, but there is no measure of rumen starch digestibility or total starch digestibility in the comparison of varieties.

Shaver recognized that the leafies may have improved starch digestibility, but he suggested that more data needs to be generated to support those claims. It will be difficult, however, to generate meaningful data on starch digestibility using existing testing methods.

Leafies have been selected to have a higher proportion of soft white floury starch as opposed to the higher proportion of hard vitreous starch found in bmr and dual purpose types. During the normal chopping and processing at harvest, floury starch naturally breaks up into a smaller particle size than vitreous starch. As such, leafies provide an advantage for rumen available starch in the production of milk.

However, the wet chemistry starch test currently used to determine starch availability starts by drying samples and then finely grinding them. This makes the vitreous starch pieces contained in BMR and dual-purpose hybrids smaller than they would be after the normal chopping and processing. As a result, this gives them an inflated test result for rumen starch availability. Of course, a cow has neither a drier nor a fine grinder in her digestive system.

The misinformation created by current testing methods which estimate starch content and starch digestibility only works to the disadvantage of dairy farmers. It is time to start the discussion on how to fix these starch analysis problems.




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