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Covering Your Bunker Silo: It’s a No Brainer

Paul Porter, Ph.D., Land O’Lakes

What are the most common reasons dairy managers give for not covering their forages stored in bunker, trench or drive-over piles? 1) It takes too long; 2) it’s messy taking tires off; 3) holes caused by wildlife increases waste; 4) disposing of the plastic is cumbersome. While most dairy managers would say that covering is the right thing to do, the fact that many still do not cover simply means they don’t believe the headache of covering is worth the benefit. When the economics become so overwhelming in favor of covering, the excuses disappear. Did you realize that not covering your bunker silo is equivalent to:

• $30 to $40 per cow per year extra feed loss, depending on the value of forage, or

• paying $20 - $25 /ton too much for your custom protein mix, assuming a 10 lb. daily feeding rate, or

• $10,000+ per 300 cows per year

The research team at Kansas State University, led by Dr. Keith Bolsen, has documented the stunning losses of feed in the top 3 to 4 feet of an uncovered bunker. In side-by-side bunker silos with similar forage and packing techniques, 50% to 65% of the feed in the top 4 feet is lost in an uncovered silo 6 months after harvesting. The covered piles averaged 12 to 20% losses. For those of us who have seen uncovered bunker silos with only a 6 to 8 inch spoiled layer, those numbers might seem unbelievable. Our eyes only tell us part of the story. Here’s what our eyes miss: 1) the next layer (18 to 36 inches) of feed is not normal: it is considerably higher in fiber and ash and lower in energy and protein; 2) the whole pile has shrunk or settled by a foot or more. When these factors are included, most the top 2 feet of your bunker silo is lost if you don’t cover it!

A 40’ x 150’ x 10’ silo pile should contain enough forage DM to feed 100 cows for 1 year. Multiply the above losses by the appropriate factor for your herd. For more detailed information on the above calculations, see pages 7-11 in the Proceedings of the 1999 Four-State Applied Nutrition & Management Conference (800 562-3618, e-mail MWPS@iastate.edu)

The keys for great bunker silo management:

1) Inoculate with a proven product (e-mail kbolsen@oz.oznet.ksu.edu for an Excel spreadsheet documenting the value of using a proven inoculant)

2) Pack. Multiply the tons per hour delivered to bunker by 800 to get the pounds of tractor(s) needed during packing. Spread out smooth, shallow layers. Alternatively, divide the weight of the packing tractors by 800 to get the tons per hour that can be adequately packed. 3) Seal. The cost of a 6 mil polyethylene film is estimated at $220 per 40’x100’ sheet with 20 hours of labor assumed for covering AND uncovering. A $400 investment to save $1400 to $2500 worth of forage. At this time, no other material functions as well as plastic. 4) Manage the face. Remove an adequate amount each day (6 inches per day) from the entire face, keeping it as smooth as possible and leaving no loose feed at the bunker floor at the end of the day.

Table 1. % lost in lost tons of feed(1) value of lost feed(2) top 3 ft. in 40’x150’ pile corn silage haylage covered immediately 12-20% 16 to 27 $400-$675 $640-$1080 covered within 2 weeks 20-25% 27 to 34 $675-$850 $1080-$1360 not covered 50-65% 67 to 88 $1675-$2200 $2680-$3520 1: assumes 45 pounds as fed per cubic foot

When & how do you cover? Ideally, you want to minimize the exposure of the silage to air and precipitation. Covering within a day or two is recommended. If a heavy rain is imminent, then covering becomes a top priority. However, if it doesn’t get done in a day or two, don’t give up. Covering within a week or two still provides significant improvements in DM recovery comparing to not covering at all (Table 1). The goal of covering is to have no air movement under the plastic. This is accomplished by placing tires virtually touching one another or adequate soil or other compound along the edges. To minimize the clutter of uncovering, create a mobile stack of tires by fixing a small post in the center of a pallet. Using tires sliced tires or large tires with squares punched out of the side walls reduces the amount of water collected in the tires.

Do you feed the crud layer? In case the answer isn’t obvious, the answer is NO! This slimy, stinky, putrid stuff does more harm than simply taking up room from good feed in the TMR. Kansas State research with growing steers demonstrated that daily dry matter (DM) intake was reduced when as little as 5% of the total silage offered was from the crud layer. DM intake was reduced even further when 10% of the silage was crud. At 15% “crud” the rumen mat was destroyed. What impact will that have on your dairy cow’s production? If you have covered a pile in the past and the spoiled layer looks to thick to you, then chances are: a) it wasn’t packed well, b) the forage was not the right moisture, c) the pile wasn’t covered with enough tires to keep air out.

In the end, the choice is simple. Either prepare mentally and physically to cover your bunker or simply use the top 1-1 feet of forage as your cover.

What does it take to remain profitable in dairying? For starters, it is applying the technology that we know works and has a high payback, such as covering your forage piles. If you choose not to employ these proven management practices, then you forfeit your right to tell your suppliers (feed, veterinarian, nutrition advisor, milk house supplies, agronomic inputs, etc.) that their prices are too high or their services are too expensive.