Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University
The primary goal of processing grain is to enhance nutrient digestion, optimize animal production, and ultimately increase profitability. We can grind, ensile, and steam flake grain to improve nutrient digestion but not all grain processing leads to identical digestibility characteristics or performance results. Some processes lead to more rapid starch degradation than others which change site of digestion and the downstream metabolic processes involved in putting milk into the bulk tank. Thus, selecting which grain processing approach suits you depends on the details: the whole diet, the cows its being fed to, and what the goal for that group is. Selecting the best grain processing method also requires understanding some details of each processing method.
1. Grinding
The simplest way to process grain is to reduce its particle size by grinding. Reducing particle size of grain can be achieved using a hammer or a roller mill. Each has advantages and disadvantages. One primary difference that will be apparent at the farm is that roller mills produce a more uniform particle size than hammer mills. Whether this is important for production outcomes from livestock consuming ground grain is not known.
Reducing particle size of grain increases the surface area that is accessible to microbes and enzymes which should enhance digestibility of the grain. Reducing particle size certainly increases the digestibility of corn grain analyzed in a laboratory. For example, as the particle size is reduced, both 7 and 16 h ruminal starch degradability increase (Goeser and Shaver, 2020).
When feeding corn grain of different particle sizes to a cow, we can expect some changes as well (Ferraretto et al., 2013). Dry matter and starch digestibility increase as particle size is reduced from 4,000 to <1,500 μm, but increased digestibility was not observed for reductions beyond 1,500 μm (Figure 1). In this meta-analysis, milk yield and milk component yields were similar for each particle size group, but milk urea nitrogen (MUN) was reduced as particle size of corn grain was reduced.
Figure 1. Effect of particle size on total track digestibility of starch (Ferraretto et al., 2013).
More recently, a team in Canada observed that reducing corn grain particle size from 1,080 to 730 μm increased digestibility, but there were not differences in milk or energy-corrected milk yields. They observed that milk protein yield was 40 to 80 g/day greater when feeding corn grain at 840 μm particle size compared to 730 or 1,080 μm particle size. This experiment did have abnormally low milk component concentrations so take the results with a grain of salt (Ahmadi et al., 2020). Particle size investigations may need to be conducted with higher milk component producing cows to be more translatable to current production norms.
Ideal Particle Size?
Many dairy farms are feeding grain that is much smaller than was previously investigated by researchers. We need to update our research of corn grain particle sizes to investigate how grain particle sizes of <1,000 μm affect animal performance. The particle size of corn grain should certainly be less than 1,500 μm, with some data suggesting that 800 μm was optimal for milk protein production. Additional reductions in particle size may be beneficial, but there are not concrete peer-reviewed data to suggest that.
2. Ensiling
We can also ensile grain as “high-moisture” to enhance the digestibility and change characteristics of the feed. For this article, I will be specifically focusing on high moisture corn.
The corn kernel dry matter should be between 28 and 32% when harvesting for high moisture corn. Corn grain harvested too wet may cause instability or heating at feed-out while too dry of kernels would reduce starch digestibility and increase risk of improper fermentation.
High moisture corn increases the rate of starch degradability compared to dry corn which usually results in an increase in ruminal starch degradability. In one example, in vitro 7-h starch degradability for dry ground corn was 44% but 62% for high moisture corn (Albornoz and Allen, 2018). Other factors also contribute to the increase in degradability, such as corn maturity. The increased degradability of high moisture corn is also reflected when feeding cattle. In a study with steers, ruminal starch degradability was 90% for cattle fed high moisture corn, whereas ruminal starch degradability was 78% when dry ground corn was fed (Galyean et al., 1976). If ensiled properly, high moisture corn can increase starch degraded in the rumen.
The increased rumen degradability presents risk, too. With more rapid starch degradability and more rumen fermentation, there is a risk for ruminal acidosis and milk fat depression. Less total diet starch should be fed if dairy cows are being supplied high moisture corn that was properly harvested and ensiled. Dairy cows consuming high moisture corn had reduced feed intake, milk yield, and milk fat yield compared to dry ground corn in a diet with 28% starch (Albornoz and Allen, 2018).
One final consideration to keep track of when feeding high moisture corn is storage time. As storage time increases, the degradability of the corn will increase (Gomes et al., 2020). A newly ensiled high moisture corn will feed differently than one that has been in a silo for a year. The diet should shift accordingly by reducing the rumen fermentable starch supplied in the ration.
3. Steam Flaking
Another option for processing corn grain is through steam flaking. Steam flaking is a process by which corn grain is subject to steam then passed through a set of rollers to flatten the kernel. This process disrupts the starch-protein matrix and thus increases starch degradability of the grain.
Steam flaking increases the ruminal degradability of starch compared to dry rolling or grinding corn grain. It does not increase ruminal starch degradability as much as ensiling the corn grain as high moisture corn. The ruminal starch degradability was 83% for steam-flaked corn compared to 90% for high moisture and 78% for dry rolled corn (Galyean et al., 1976). In a recent study in Canada, feeding steam flaked corn resulted in similar feed intake and component milk yields compared to feeding dry ground corn that ranged from 730 to 1,080 μm (Ahmadi et al., 2020).
Take-Homes
Be strategic when selecting your starch source and processing method. If you simply want to maximize ruminal starch digestibility, then high moisture ensiling of grain at proper moisture may be most promising. Feeding such highly fermentable starch comes with risks of ruminal acidosis and milk fat depression. If you’re feeding more fermentable starches, like high moisture corn, you probably should reduce the total diet starch and increase dietary NDF or forage NDF compared to if you’re feeding dry ground corn.
If you’re feeding dry ground corn, it must be less than 1,500 μm. Most feed mills will meet this expectation, but due diligence is always a good idea. Further reductions in particle size may be beneficial, but the peer-reviewed data need to catch up to provide a clearer recommendation.
One last note - if you’re changing starch sources in the diet by switching the processing, then you need to pay attention to your cows. Keep close attention to feed intake, milk yield, milk fat concentration, MUN, and rumination (if you have a monitoring system). Based on these factors, you may need to make dietary adjustments like increasing NDF, forage NDF, or reducing starch and rumen fermentable starch.
References
Ahmadi, F., G.R. Ghorbani, A. Sadeghi-Sefidmazgi, M. Heydari, H. Rafiee, and K.A. Beauchemin. 2020. Performance and feeding behavior of dairy cows fed high-concentrate diets containing steam-flaked or ground corn varying in particle size. J. Dairy Sci. 103(4):3191-3203. https://doi.org/10.3168/jds.2019-17344
Albornoz, R.I. and M.S. Allen. 2018. Highly fermentable starch at different diet starch concentrations decreased feed intake and milk yield of cows in the early postpartum period. J. Dairy Sci. 101(10):8902-8915. https://doi.org/10.3168/jds.2018-14843
Ferraretto, L.F., P.M. Crump, and R.D. Shaver. 2013. Effect of cereal grain type and corn grain harvesting and processing methods on intake, digestion, and milk production by dairy cows through a meta-analysis. J. Dairy Sci. 96(1):533-550. https://doi.org/10.3168/jds.2012-5932
Galyean, M., D. Wagner, and R. Johnson. 1976. Site and extent of starch digestion in steers fed processed corn rations. J. Anim. Sci. 43(5):1088-1094.
Goeser, J.P. and R.D. Shaver. 2020. Commercial ground corn grain samples vary in particle size metrics and in situ rumen starch digestibility. Applied Animal Science 36(5):610-614. https://doi.org/10.15232/aas.2020-01981
Gomes, A.L.M., A.V.I. Bueno, F.A. Jacovaci, G. Donadel, L.F. Ferraretto, L.G. Nussio, C.C. Jobim, and J.L.P. Daniel. 2020. Effects of processing, moisture, and storage length on the fermentation profile, particle size, and ruminal disappearance of reconstituted corn grain. J. Anim. Sci. 98(11). 10.1093/jas/skaa332