Can Forage Fiber be Too Digestible?

March 23, 2018 03:51 PM
Low-lignin alfalfa and BMR corn silage beg the question.

As farmers incorporate both BMR corn silage hybrids and low-lignin alfalfa varieties into their rations, some are wondering if forage fiber can become too digestible. “We don’t have a good answer, especially when these forages are fed in combination,” says David Combs, a dairy Extension nutritionist with the University of Wisconsin.

In many cases, brown midribbed corn (BMR) total tract neutral detergent fiber digestibility (TTNDFD) can exceed 45% while conventional corn typically ranges from 40% to 45%. BMR usually runs three to four percentage points higher than corn silage, but there can be overlaps where conventional corn surpasses BMR due to growing conditions or other environmental effects, Combs says.

Randy Shaver, also a University of Wisconsin dairy Extension nutritionist, summarized a number of trials comparing BMR corn to conventional, high-fiber digestible and leafy hybrids. Cows fed BMR corn had higher dry matter intake and milk yield, while fat and protein percent were not affected.

What about feeding low-lignin alfalfa with BMR? Low-lignin alfalfas typically have two to three percentage units higher digestibility than conventional alfalfa.

Like conventional alfalfa, fiber in low-lignin alfalfa increases and digestibility decreases as the low-lignin varieties mature. But the low-lignin types start at a lower level. Farmers can gain quality by harvesting low-lignin varieties on the same schedule or delay harvest a week to get the same quality as conventional varieties but pick up yield.

Shaver surveyed dairy nutritionists to see their experiences with feeding the two high-powered forages. Only one nutritionist had fed BMR corn silage and low-lignin alfalfa for at least three years. None reported significant issues.

Shaver recommends farmers not make major ration changes if they are already doing a good job of harvesting, ensiling and managing rations.

“Fiber and digestibility are greatly affected by weather and the timing of harvest,” Shaver emphasizes. Conducting routine and accurate forage sampling and analysis is critical to knowing feed quality in order to correctly balance rations, he says.


Note: This story ran in the March 2018 magazine issue of Dairy Herd Management.

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