September 5, 2017 at 3:32 p.m.

Forage digestibility variations affect performance

David Weakly, Ph.D.,<br /><!-- 1upcrlf -->Forage Genetics International
David Weakly, Ph.D.,<br /><!-- 1upcrlf -->Forage Genetics International

By by Ruth Klossner- | Comments: 0 | Leave a comment

SIOUX FALLS, S.D. - David Weakley, Ph.D., Director of Dairy Forage Nutrition Research for Forage Genetics International, addressed feed efficiency and milk production issues at the Central Plains Dairy Expo in Sioux Falls, S.D., March 28 and 29. His presentation, "Using Rumen Digestibility Data to Improve Intake, Feed Efficiency, or Diet Costs for Lactating Cows," described new tools available to nutritionists and dairy producers to improve cow performance and better utilize forages.
In opening his presentation, Weakley noted that efficiency of nutrient conversion is vital to the dairy industry. He said, "How do we maintain the demand for meat and milk with a fixed land base and competition for grains?"
To do so, animal production systems must become more efficient, getting the same amount of production with fewer acres or animals, or get increased production with the same number of animals and acres. They must do it with less starchy grains (corn, milo, small grains, etc.) and more forage in the diet.
Increasing production is one way to make cows more efficient. To get 10 pounds more milk per cow, for example, producers can increase energy density, increase dry matter intake (DMI), or both.
Weakley said that uncontrolled on-farm variations in forages, starch, and protein can compromise milk production and lower efficiency. Those variations can account for 65 percent of on-farm variations in fat corrected milk. They must be understood, measured, and controlled to ensure predictable performance.
Dry matter intake and digestibility in dairy cows are influenced in great part by the consequences of ruminal digestibility of starch and fiber. Too much starch digested in the rumen can cause a shift in energy partitioning towards body fat deposition, decreased DMI, and reduce neutral detergent fiber (NDF) digestibility.
Ruminal starch digestion can be influenced by a variety of factors, among them grain source, moisture content, grain processing, endosperm type, level of grain in the diet, and total dietary dry matter. Those factors influence dietary crude starch recommendations.
However, formulating to crude starch and fiber dietary standards does not account for variation in ruminal digestibility, potentially leading to differences in cow performance. Rather, a method for rapid testing of ruminal digestibility of ingredients, combined with formulating to dietary targets, can improve feed efficiency and animal performance.
Forage Genetics, International's program, Calibrate® Technologies, looks at neutral detergent fiber (NDF), which represents the cell wall content of forages in the diet. This, along with the starch content of ingredients and their in vitro ruminal digestion (GPN and FPN) are measured in the Calibrate® Technologies In Vitro Lab.
The variation in the NDF digestibility of forages can affect milk production by affecting intake.
"The traditional way most nutritionists try to account for that variability is to measure the crude NDF content of all forages and formulate combinations of those ingredients to meet a dietary standard for either NDF or forage NDF," Weakley said. "Unfortunately, that doesn't take into account the digestibility of those forages. We developed a system to measure those differences in digestibility and compare them to formulation targets in the diet. It's the amount and digestibility of the NDF that's important, as this influences its contribution to rumen fill, intake, and total diet digestibility."
Testing has shown a tremendous variation in the starch and ruminal digestibility (GPN) for various feed ingredients. GPN ranges from 1 (slow or low) to 11 (fast or high ruminal starch digestion). Ground dry shelled corn ranges from 1 to 6, high moisture corn from 2 to 10, and corn silage from 5 to 11. Likewise, percent starch varies greatly. Corn grain ranges from 63 to 75 percent. In addition, it was found that there is no relationship between starch and GPN in corn grain samples. Furthermore, the GPN for corn silage increases slightly over time from harvest, but that rate varies by year, according to the research.
Ruminal starch degradability varies month-to-month and year-to-year and can negatively affect production. Measuring and stabilizing this source of variation offers opportunities to improve dry matter intake, improve milk components, and reduce the level of corn in the diet.
Forage fiber digestibility drives intake. As NDFD increases, dry matter intake potentially increases. Weakley pointed out a literature survey by Oba and Allen, 1999, that found that a one-unit increase of in vitro digestibility of NDF was associated with a 0.37 lb/day increase in dry matter intake (DMI) and a 0.55 lb/day increase in four percent fat corrected milk yield per cow. Studies have also shown that greater DMI responses are observed with early lactation, higher producing cows that are more bulk fill limited. The responses are less noticeable with lower producing cows.
Using forage NDF digestibility factors, diets can be optimized to increase DMI and milk production or to increase digestibility and feed efficiency.
Studies of 28-hour in vitro ruminal digestion (FPN) at the Calibrate® Technologies In Vitro Lab found tremendous variations in NDF and its digestibility (FPN) for various forages. FPN ranges from 60 (slow or low) to 180 (fast or high ruminal NDF digestion).
Corn silage ranged from 135 to 165, wheat silage from 115 to 170, sorghum silage from 130 to 160, alfalfa hay from 115 to 150, and cottonseed hulls from 60 to 75. Corn stalks had a higher digestibility than one might expect-115 to 140.
Wheat silage, which Weakley called the "star of digestibility," has a relatively wider distribution in digestibility, but is generally higher than most other forages.
Studies found that one way to increase total NDF digestibility was to include three percent straw in place of alfalfa hay in diets with inadequate NDF fill. The straw slowed the passage rate through the rumen, allowing for more complete digestion.
The presentation concluded with a summary of the value of the Calibrate® program to dairymen. Those values include ingredient cost savings (substituting high cost ingredients with lower cost ingredients), milk composition diagnosis, absence of Sub-Acute Ruminal Acidosis, informed/improved economic evaluations, input management (hybrid selection, harvest management, and storage management), increasing dietary energy safely, inventory management, increasing dry matter intake (DMI) and production, increasing feed efficiency, and increasing dietary forage levels.
Weakley's presentation was sponsored by Land O'Lakes.[[In-content Ad]]


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