Choosing a corn silage can be tricky.
Should you use a BMR (brown midrib) or non-BMR hybrid? They each have their advantages and disadvantages. BMRs cost more money, but they also result in better fiber digestibility. Non-BMRs cost less money and can even yield better than some BMRs — but they produce more lignin, which can decrease digestibility.
This is a straightforward way of evaluating two distinct kind of hybrids, but most farmers know that other factors must be considered.
Mike Miller, research technician at the Miner Institute in Chazy, N.Y., says it’s about “clearing up the foggy windshield” to get to a simple decision based on economics.
Between 2015 and 2017, the Northern New York Agricultural Development Program funded an evaluation of five corn silage hybrids — three BMR and two non-BMR — on a 14-acre tile-drained research farm.
Speaking at World Dairy Expo, Miller said the purpose of the trial was not only to evaluate yield, but also to compare forage quality between varieties.
Researchers first evaluated starch as a percentage of dry matter, and calculated starch yield by multiplying the starch content by total yield.
They then evaluated neutral detergent fiber (NDF), undigestible NDF (udNDF) — the stuff that cows don’t eat — and potentially digestible NDF (pdNDF), which is the difference between the digestible and undigestible fiber and can be key to evaluating hybrid performance.
The non-BMRs yielded better in most trials, but it varied depending on year and weather conditions. Starch levels were higher in the non-BMRs, as were the starch yields. The levels of NDF as measured by percentage of dry matter were slightly higher in the non-BMRs, but udNDF values were also higher, meaning that the amount of potentially digestible NDF was lower in the non-BMRs.
“You can have a high yield of fairly indigestible stuff and guess what — your cows can only eat so much and you’re limited. Or, you can have really high-quality stuff with a crazy low yield. It really depends,” he says.
But does this tell the whole story? Not quite.
“This is very important to look at — but again, you're still looking through a foggy windshield,” he says. “You’re not seeing the full picture.”
So, the researchers decided to take it another step.
“Producers want to see something that’s simple and easy to understand,” he says.
They calculated the cost of corn silage per ton based on seed, planting, fertilizer, chopping and hauling.
They also calculated the cost of nutrients per ton based on NDF, udNDF240, pdNDF, starch and rumen-fermentable starch.
The BMR costs were higher based almost solely on seed costs, and the yields were highest in one of the non-BMR varieties.
But how much did the cows eat, and which varieties were more economical? This got complicated when looking at udNDF240, which was higher in the non-BMRs. The amount of pdNDF was higher in the BMR varieties.
“So what does that mean? That means you’re putting the money toward what the cow can access, instead of just putting money toward stuff that just ends up in your manure pit,” he says.
Simplifying the data
The final step, Miller says, was developing a formula to come up with a number that farmers can easily understand: income over feed cost.
He chose a high-producing group of cows: 60 pounds of dry matter intake a day producing 100 pounds of milk per day.
The formula included the cost of corn silage — 35% corn silage in the diet — a total feed cost based on other ingredients in the diet, and an initial income-over-feed cost based on $16 cwt milk. The initial income-over-feed cost calculation showed non-BMRs with a slight advantage.
He then calculated a new cost of feed and income-over-feed cost based on predicted NDF digestibility and how much more milk could be produced.
Since BMRs have increased digestibility, he wanted to account for that, as well as more milk that could be produced.
The formula spit out new income-over-feed cost calculations that showed higher values for the BMR varieties compared to the non-BMR varieties.
The foggy windshield on corn silage evaluation, he says, got clearer.
“It’s not percentage dry matter and adjusted yields; it’s these nutrient yields that really matter: NDF and pNDF yields I think are really vital,” he says.
Miller says other factors can be considered by farmers when trying to evaluate what corn silage varieties are better suited for their operation. The bottom line, he says, is to consider all the data and not just rely on seed cost and yield.
“We’re in the age of so much data; how many different corn silage hybrid evaluations do you see a year? A lot. And it’s not just like 10 hybrids, it’s hundreds of hybrids. And then try to go through all of it,” he says. “I’m just trying to help you start to help you manage that and look through it.”
To access the formula Miller used and to insert your own numbers, go to bit.ly/2BgfY25.