What’s new in forage research?
|By Luiz Ferraretto|
Forage research continues to evolve and unlock answers to current dairy cattle feeding questions.
The author is an assistant professor and ruminant nutrition extension specialist at the University of Wisconsin-Madison.
Forages are the main ingredients used in dairy cattle diets. Producing high-quality forages is vital for dairy profitability and sustainability. As such, many research trials about this topic are presented yearly during the annual meeting of the American Dairy Science Association, and this year was no different. The objective of this article is to describe and discuss some of the forage research presented. For full disclosure, these are only a few of the many research trials presented and were hand-picked to represent different areas within forage research.
Picking a method for forage analysis: Regardless of your role within the forage industry, you’ve probably had to submit samples for nutrient analysis or made decisions based on those results. Many farmers and nutritionists submit samples for analysis routinely. But when it comes to forage analysis, turnaround time, costs, and the reliability of the methodology used are all key factors in determining how to analyze forage samples. It is undeniable that analyzing forage samples via near-infrared spectroscopy (NIRS) is faster and cheaper than by wet chemistry methods. However, forage growers, dairy producers, and nutritionists always wonder “Is NIRS analysis as accurate as wet chemistry?” or “Can we rely on NIRS analysis for this specific crop or conditions?”
Researchers from Canada conducted a three-year study trying to answer these questions for first-cut legume-grass silage. Briefly, 202 samples were collected from Canadian dairy farms between 2018 and 2020, and subsamples were sent to a commercial laboratory for NIRS and wet chemistry analyses. No differences between methods were observed for crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and fat, but ash was slightly higher (1.6 percentage units) for wet chemistry than NIRS. The authors concluded that NIRS is sufficiently accurate for nutrient analysis of first-cut legume-grass silage.
Keep in mind that regardless of which method you pick, analyzing samples with the same method and laboratory allows for an apples-to-apples comparison and ensures the decision-making process is based on accurate information.
Industry struggles with sorghum silage processing: Sorghum silage has been growing in popularity and is being fed by more and more dairy operations. But losing grain in the feces has been one of the biggest, if not the main, challenge faced by producers. A survey collected 53 sorghum silage samples from commercial farms between January and February of 2022. Samples were analyzed for berry processing score (the equivalent assay to kernel processing score widely used for corn silage but adapted for sorghum) and nutrient composition. Berry processing score (percent of starch passing through a 2.36-mm sieve) averaged 20% and ranged from 7.2% to 54.8%. These values highlight berry processing has been minimal in commercial operations. Although we cannot determine which factors are associated with these results, the most common factors impairing processing are maturity at harvest, harvester settings, and lack of monitoring.
Sorghum berry size is another factor compromising processing in sorghum silage. Because berries are small, even forage harvesters set with adequate chop length and kernel processors (based on corn silage standards) struggle to achieve high berry processing scores.
Research conducted in West Texas evaluated processing and starch digestibility of two sorghum hybrids, one with larger berry size and another with smaller berry size. Even though berry processing was slightly lower for the larger berry hybrid, starch concentration and digestibility were identical. Because berries were much larger for the larger berry hybrid, as expected, these results suggest perhaps larger berries were broken into more pieces to reach a similar score and starch digestibility. More research is required to better understand if larger berries will help achieve adequate processing.
Fiber digestibility and particle size: Despite being available for several years, the undigestible NDF (uNDF) assay remains the new kid on the block regarding forage research and analysis. This method measures the amount of NDF undigested after a certain period (240 hours is the most common) of incubation in rumen fluid and is often used as a replacement for lignin.
Researchers from New York compiled data from seven feeding trials for a total of 22 diets to determine the relationship between uNDF and performance. Forages included in those diets were corn silage, haycrop silage, timothy hay, and wheat straw. Increasing amounts of uNDF in the diet moderately lowered intake and energy-corrected milk production. But predictions of intake and energy-corrected milk were improved when physically effective fiber was combined with uNDF and used in predictions, highlighting the importance of fiber particle size in dairy rations.
A study from Brazil evaluated the physical effectiveness of corn silage particles. Researchers sieved corn silage through a Penn State Particle Separator (19 millimeters [mm], 8mm, and pan) and added particles coarser than 19 mm, between 8 and 19 mm, and finer than 8 mm to a basal diet. This study revealed particles between 8 and 19 mm were more effective at stimulating an adequate rumen environment than other fractions. This is because cows sorted against particles coarser than 19 mm. When formulating diets based on the 19 mm screen, evaluating sorting routinely is recommended. This study also confirmed the effectiveness of corn silage particles finer than 8 mm, but these particles were still less effective than coarser particles.
Corn silage chop height affects fermentation: Raising chop height is a well-known harvesting practice to achieve greater nutritional value at the expense of yield. When forage inventory permits, increasing chop height reduces lignin, NDF, and uNDF concentrations while lowering starch concentration and NDF digestibility. But raising the chop height also reduces moisture, which could affect fermentation.
Two studies evaluated this effect. The first study, conducted in Illinois, harvested brown midrib corn silage at 12 or 22 inches of chop height. Even though increasing chop height improved nutritive value, the lower cut silage had improved fermentation. A similar study, conducted in Wisconsin, compared conventional corn silage harvested at 10 or 25 inches in height. Nutritive value improved with higher chop, but total acids concentration was reduced. Both studies also evaluated different microbial inoculants and observed improved fermentation with inoculation.
Combined, these studies underscored that increasing chop height remains a great tool to improve nutritive value of corn silage when forage inventories permit. However, fermentation will be slightly less pronounced compared with lower cut silage and the use of a research-proven microbial inoculant is advised.
This article appeared in the November 2022 issue of Hay & Forage Grower on pages 20-21.
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