Sally A. Flis, Ph.D. – Feed and Crop Support Specialist, Dairy One
When we discuss silage pile shrink, most of the time we are talking about wet weight shrink, which is measured as the difference between the amount of feed delivered to the bunk at harvest versus the amount of feed that makes it to the cows. This amount of feed represents the cumulative losses of fermentation (water and nutrients), spoiled feed, and losses during feed out. If you are not measuring your losses, it is hard to manage for loss prevention.
At the Western Dairy Management Conference in March this year, Dr. Peter Robinson from UC-Davis talked about some changes to California laws that are identifying silage piles as contributors to air pollution Rule 4570. Dr. Robinson has done on-farm research with rollover piles, bunker silos, and wedge piles to see how much volatile organic compound losses are occurring.
In the project, they measured the wet weight shrink, oven dried shrink, and oven dried shrink corrected for volatile compound loss (not including spoiled/waste feed). Oven dried shrink is the dry matter equivalent of the wet weight shrink. A concern in the use of this measure is an overestimation of loss due to the loss of volatile compounds during drying. The volatile compounds commonly found in silages are alcohols (i.e.: ethanol, methanol, propanol, and butanol), esters (i.e.: propyl acetate, ethyl butyrate, and methyl acetate), alkenes, aldehydes, ketones, and carbonyl compounds like formaldehyde.
The average losses across the 8 piles monitored were 8.4 ± 1.59 % for wet weight, 6.8 ± 1.82 % for dry weight loss, and 2.8 ± 2.08 % for volatile corrected dry matter loss. These results show that most of the loss measured in the wet weight is water loss, and that in the dry matter loss contains a lot of the volatiles driven off by the oven drying.
Considering the data from this work, how you measure shrink is dependent on what you want to know. For feed inventory management, knowing total loss is important, since we store feed with moisture in it and we feed out with moisture in it. For comparing inventory to formulated rations, knowing dry matter loss including volatile compounds is useful because rations are formulated on a dry matter basis that is derived in the same way as dry matter for loss calculations.
In most states, the volatile compounds lost from silage storage are not regulated, and more research needs to be done to understand what volatile compounds are lost, when they are lost, and how.