Storing wet forage sabotages silage quality

Chopping small grains in the spring is one way to bolster silage supplies for the rest of the year, but doing so can invoke a lot of questions and options. When is the best time to harvest? How long should forage wilt before it is put into storage? Does the silage need to be inoculated?

Plant maturity at harvest, wilting duration, and storage practices ultimately determine silage quality at feedout. To demonstrate this, researchers at the University of Nebraska recently collected small grain forage samples from 17 farms in the Cornhusker State after harvest and again after fermentation to quantify changes in nutrient content.

After harvest, half of the samples were 30% to 35% dry matter, which is within the target moisture range for small grains. Forty percent of samples were considered too wet, and 10% were too dry. After fermentation, the survey data shows energy loss was between zero and 17 percentage units of total digestible nutrients (TDN) across all of the samples in the study.

A team of extension educators and specialists with the University of Nebraska explain the silage that was too wet at packing had the greatest TDN loss. In fact, the wet samples had almost three times that of silage that was packed within the target moisture range. Clostridial fermentation is likely to blame.

“Silage that is packed too wet can have the wrong type of fermentation, in which clostridial bacteria use the nutrients in the forage to grow and produce butyric acid. This reduces palatability and feed value of the silage,” the authors explain.

Moreover, forage that undergoes clostridial fermentation will never be properly preserved and TDN will continue to decline during storage. So, how can farmers prevent this energy loss?

Wilting and inoculation

The key to high-quality silage is allowing small grains to wilt long enough based on plant maturity and weather conditions. For instance, more mature forage will have a higher dry matter content and require less drying. The combination of temperature, wind, and relative humidity can positively or negatively affect wilting, too.

“Based on the survey data, producers who wilted small grains that were harvested at boot, heading, or pollination stages for 16 to 24 hours appeared to be more likely to achieve targeted dry matter content,” the authors state. On the other hand, forage samples in the milk or soft dough stage only needed two hours of wilting — at most — for desirable results.

Applying inoculant can defend against rapid declines in energy loss during storage. For example, the wet forage samples in the study that were packed without an inoculant lost approximately 11.2 percentage units of TDN, whereas wet silage that was inoculated only lost 5.9 TDN units.

When survey participants applied inoculant to forage samples within the target moisture range, it had little effect on energy loss at feedout. The authors suggest this is likely because energy loss was already relatively low.

“Reaching the target dry matter range prior to packing is always best; however, silage inoculants can be useful insurance,” the authors assert. “For small grain silages, the biggest challenge is achieving a rapid drop in pH to preserve the forage. Therefore, using a homolactic acid-based inoculant is recommended.”

Amber Friedrichsen

Amber Friedrichsen served as the 2021 and 2022 Hay & Forage Grower summer editorial intern. She currently attends Iowa State University where she is majoring in agricultural communications and agronomy.