There are many different ways to assess dairy and feedlot performance and profitability. In the dairy industry, milk yield per cow has been the classic performance indicator; however, new age key performance indicators such as feed conversion efficiency (FCE), FCE based upon energy-corrected milk, or income over feed costs are now the preferred performance measures.
Similarly, there are numerous particle size measures relevant to dairy or beef nutrition to help us manage forage and cow diets, and these particle size measures are also evolving with new research and development. The various particle size measures relate largely to fiber and starch, which are important to understand as carbohydrates drive dietary energy in dairy and beef rations.
The breakdown
Corn silage and snaplage kernel processing score (KPS) continues to be a leading topic among dairy and beef producers, nutritionists, forage growers, and customer forage harvesters. Case in point, a forward thinking dairy producer in Florida checked in with me just the other day to get my thoughts on processing and their farm’s measures. They are aiming for complete kernel destruction, understanding that corn silage KPS is positively related to rumen and total tract starch digestion. Leading harvesters now achieve 75% to 80% KPS when benchmarking fermented silage or snaplage.
Corn silage KPS has been related to fecal starch and corn bypassing through cattle. In years past, with cheaper corn and better margins, 2% to 3% fecal starch in dairy cows had been acceptable. However, when seeking performance gains with razor-thin margins, there is zero room for grain to pass through undigested.
The goal for fecal starch in dairy cows is now less than 1%. For beef cattle, the top 15% of samples analyzed by Rock River Laboratory are less than 3% of dry matter. Beyond corn silage KPS, corn grain mean particle size and surface area are also related to fecal starch and starch digestibility. We’ll stay focused on forage measures here, although it’s important to understand that particle size in all the grain- and starch-rich ingredients are important if you’re not hitting your fecal starch benchmarks. With this in mind, sorghum silage can also contribute substantial starch to dairy diets in drought-stressed regions or years.
Berries are challenging
Sorghum and other berry-producing warm-season grasses are substantially more water efficient, and they are gaining momentum as dairy or beef forage crops. Historically, nutritionists have discounted the starch content in these silages due to poor or zero berry processing. Corn silage kernel processors are mostly ineffective in breaking the much smaller sorghum berries. Therefore, despite the silage containing 15% to 20% starch, the starch has historically been poorly digested due to unprocessed berries in the silage.
This is now changing as novel berry processors are being developed and tested. My colleagues Mike Brouk, Jared Johnson, Juan Pineiro, Luiz Ferraretto, and Katie Raver, among others, have expected this mechanical engineering development, and they have collectively helped bring forward a research-backed berry processing score. This berry processing score is now the particle size assessment for sorghum and other berry producing silages. We’ll cover this particle size measure more in a future column, but initial studies suggest that berry processing scores at 50% to 60% are achievable with advanced machinery.
Fiber factors
Transitioning from starch to fiber, forage fiber particle size is equally important. Penn State particle size analysis, with the Penn State shaker box, continues to be one of the most valuable measures for forages. While kernel or berry processing score and grain particle size affect feed energy value, the fiber particle size affects packing density, forage mixability, and animal eating behavior and health. Structural fiber is necessary for rumen health, but fiber particle size also affects diet passage rate through the digestive tract and fiber digestibility.
I’m routinely consulted for particle size recommendations with haylage or silage, but my recommendation always sounds academic: “It depends!” While smaller particle size in grain is always better, fiber particle size goals depend on many different factors and considerations, including silo storage structure, forage maturity and fiber digestibility, whether other fibrous feeds are available, forage-to-grain ratio in the diet, feeding practices, feed management, and more. The bottom line is that forage particle size recommendations are situation dependent.
The structural fiber also interacts with fiber digestibility, and nutritionists are beginning to evaluate physically effective undigestible fiber. Rick Grant with the Miner Agricultural Research Institute in New York and his colleagues have done groundbreaking work with this newer particle size related measure. Goals for dairy diets appear to be in the 3% to 7% of dry matter range; however, this benchmark will also be dependent upon the situation and the individual dairy farm. For more insight on this, reference “The physical side of fiber” published in the April 25, 2024, issue of Hoard’s Dairyman.
In conclusion, advance your forage particle size assessment with the concepts covered here. Particle size is important for dairy and beef performance, but analyzing forage grain or fiber particle size requires the checking of a few different boxes. Much like the different dairy or beef performance benchmarks, there are a variety of particle size measures and benchmarks to ensure your forage fiber and kernel or berry processing is adequate.
This article appeared in the August/September 2024 issue of Hay & Forage Grower on page 23.
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