There are numerous strategies available to optimize fermentation, starch availability and overall quality of HMC.
By Luiz Ferraretto
High-moisture corn (HMC) is an important feedstuff to aid fulfill the energy demands of a lactating cow. Maximizing its fermentation and starch availability is key to increase its energy value. There are numerous strategies available to optimize fermentation, starch availability and overall quality of HMC. These are essential for the efficient utilization of nutrients by dairy cattle. Corn kernels have two primary factors limiting starch digestion by ruminants. Pericarp, the corn hull, is highly resistant to microbial and enzymatic degradation and is the first barrier to digestion. The second is a specific type of protein called zein, which surrounds starch granules and is barely degraded in the rumen of cattle. This article will review and discuss factors that affect the nutritive value and fermentation of HMC, as well as strategies available to producers to optimize its nutritive value and fermentation. Fermentation is more than silage preservation Ensuring a good silage fermentation is key for dry matter and nutrient preservation. Compared with whole-plant corn silage, HMC has less moisture, which is important for bacteria transport in the silo, and lower levels of sugar, the primary substrate for silage fermentation. Also, in certain areas such as the Upper Midwest, HMC is harvested in the fall when the natural bacterial population is not as viable because of cool temperatures. Thus, HMC would typically ferment more slowly and to a lesser extent than whole-plant corn silage. Boosting the initial fermentation could help mitigate this issue. Silage inoculants contain bacteria that take over the fermentation process and shift silage fermentation toward a desired pattern (mainly lactic acid and some antifungal acids) for optimum preservation. This may help in situations where the natural bacterial population is unable to dominate the fermentation process. Inoculating HMC could safeguard your crop investment. But using a product designated for HMC and research-proven is advised as these would usually contain higher bacterial counts. But fermentation of feeds rich in starch goes beyond silage preservation.
Figure 1. Effect of storage length of starch digestibility. Adapted from Ferraretto et al. (2014); Journal of Dairy Science 97:3221-3227.
During fermentation enzymes that breakdown zein proteins are released. Most of these enzymes, about 60%, are from bacteria whereas 30% are enzymes found inside corn kernels and are activated by low pH. This explains why starch digestibility is often greater in HMC than dry corn. Starch digestibility spikes during initial fermentation and continues to increase gradually with prolonged storage. But the gradual increase is not as pronounced as the initial spike. Figure 1 exemplifies this phenomenon. Briefly, a commercial dataset of approximately 6,000 samples was separated by month of sample submittal. Month of samples submittal was assumed to be associated with length of storage. Research supports inventory planning for feeding HMC only after 90 to 120 days of storage. But this practice requires optimum silage management to avoid more losses during prolonged storage.
Particle size matters Feeding whole or coarsely ground HMC to reduce labor, time, and energy costs is not unusual. But these benefits come at the expense of starch digestibility. Grinding kernels thoroughly is essential for exposing starch to digestion. Corn kernels that have been extensively processed have increased surface area available for microbial attachment and enzymatic degradation increasing starch digestibility. But this effect is not only related to surface area. Recently, we studied the effects of particle size on silage fermentation and starch digestibility of HMC ensiled for a short period (up to 28 d). In that study, concentrations of lactic and acetic acids were greater in finely ground (958 µm) compared to coarsely ground (4,448 µm) HMC. This difference is related to greater exposure of kernel sugars to microbial fermentation with finely compared to coarsely ground HMC. In a follow-up study, pH was reduced, and concentrations of lactic, acetic, and total acids were greater in ensiled corn grain with broken kernels compared to that with intact kernels. Our results from both studies suggest that this is very important as the proteolytic activity (indicated by greater concentrations of soluble CP and ammonia N) was increased when ensiled corn grain was more extensively processed. Probably because more enzymes that break zein proteins were available with a more robust fermentation. Overall, research indicates finely grinding HMC improves fermentation and starch availability.
Moisture Proper moisture at harvest is another key step to increase starch availability of HMC. Starch digestibility of HMC is positively related to its moisture concentration. More mature and drier kernels have greater proportion of vitreous endosperm, which has more zein proteins. Increased vitreousness hardens the kernel hardness, increasing its resistance to grinding or mechanical processing. But reduced digestibility is also impacted by reduced water available for the growth of bacteria in the silo corn plants mature and DM concentrations (in the plant and within the kernel) increase. Reduced concentrations of organic acids, suggesting a limited fermentation, are frequently observed in dried HMC. Recently, our laboratory conducted a study to evaluate the effect of fermentation on starch digestibility without having different vitreousness. Briefly, this was accomplished by increasing DM concentrations in HMC through oven-drying at a low temperature as an alternative to a delayed harvest. A more robust fermentation, proteolysis (based on soluble CP and ammonia-N data), and ruminal in situ starch disappearance were observed when HMC was ensiled at 35% compared to 30% moisture. Summary Production of HMC is very important to the dairy industry. Understanding the factors that affect the nutritive value and fermentation of HMC is essential for optimizing its inclusion in dairy diets. Numerous management factors influence the nutritive value of HMC, including moisture content and fineness of grind. Determining the best moisture and particle size practices for each dairy requires the assessment of equipment availability, labor, time, and energy costs.
Luiz Ferraretto, Ruminant Nutrition Extension Specialist, Department of Animal & Dairy Sciences, University of Wisconsin – Madison
