What are the different types of fiber and how do they support milk production?

Introduction

Fiber is an important part of dairy cattle diets and much confusion exists surrounding the different types of fiber found in common diet feedstuffs and how they can be leveraged in a well balanced diet. Fiber is a type of carbohydrate and successful inclusion in the diet supports overall cow health and productivity.  This article will break down the different types of fiber and how each supports milk production.

Carbohydrates and Fiber in Dairy Cattle Diets

Carbohydrates in ruminant diets can be split into two major types: non-structural carbohydrates (NSC), and structural carbohydrates. Non-structural carbohydrates, include sugar, starch, and other cell substances that make up the internal contents of plant cells. They are easily digested by rumen microorganisms, providing the cow with a quick source of energy. On the other hand, structural carbohydrates are part of the plant cell wall and are responsible for structural support, nutrient transportation, cell protection and shape. When discussing fiber, we are typically focused on the structural carbohydrate portions of the feedstuffs. And this is where things get challenging. There are many different ways that we refer to the different fiber fractions found in feeds.

Types of Fiber

Effective Fiber

Effective fiber is the portion of fiber that stimulates chewing and saliva production and depends on the diet’s particle size. Feeding only small particles (0.16-inch or less) will cause fast passage rate through the rumen and can trigger acidosis but feeding only large particles (larger than 0.31 inch) will decrease milk production due gut fill resulting in   a lack of energy and very slow feed passage rate. 

Some larger fiber particles or “physically effective fiber” (larger than 0.31 inch)—such as those found in hay and straw—are necessary, and have a beneficial impact on rumen function. In the right amount, large particles stimulate rumen contractions, increase saliva production, and support milk fat synthesis. In contrast, the lack of effective fiber can result in digestive disorders, such as acidosis and milk fat depression. To evaluate the content of physically effective fiber in a ration, farmers can use the Penn State Particle Separator. ↗️

Fiber from a lab test

When sending samples for lab analysis, the fiber results are presented as Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), and Lignin.

• Neutral Detergent Fiber (NDF), is a measure of the three main cell wall components (cellulose, hemicellulose, and lignin). In general, when the NDF value of a feed is too high, it means that feed takes up greater space in the rumen and is slowly digested, which could lead to a decrease in dry matter intake.
• Acid Detergent Fiber (ADF), measures the cellulose and lignin content.These two components are less digestible than hemicellulose. This value can be used as a metric for digestibility. If a large portion of the forage’s fiber is ADF, it will not be as digestible and will provide less energy to the cow compared to a forage with a lower ADF value.
• Lignin is an indigestible cell wall component that provides structural support to plants, helping them remain upright as they grow. As forages mature, lignin content increases to support the larger plant, but this effect reduces overall digestibility. This highlights the importance of harvesting forages at the proper stage of maturity to optimize yield and digestibility. Some forage varieties, such as BMR corn and low-lignin alfalfa, have been selectively bred or engineered to contain less lignin and improve digestibility.

Table 1: Effect of Maturity on the different types of fiber

	Early Harvest Less Mature	Late Harvest More Mature
Cell Wall	Thinner	Thicker
NDF	Lower	Higher
ADF	Lower	Higher
Lignin	Lower	Higher
Effective Fiber	Lower	Higher
Intake (Dry Matter)	Higher	Lower
Energy available	Higher	Lower

Insoluble and soluble Fiber

Insoluble fiber refers to three components of the plant cell wall we have already talked about—cellulose, hemicellulose, and lignin—that do not dissolve in the solution used in the Neutral Detergent Fiber (NDF) method. These components are not easy to digest by cows. However, the cell wall also contains a soluble part made up of digestible carbohydrates, such as pectins, fructans, beta-glucans, and even some resistant starches, those are what we refer as soluble fiber.