Corn silage enhances the diet’s energy density while supplying effective fiber, provided particle size is adequate. This energy is influenced by the digestibility of both structural (fiber) and nonstructural (mainly starch) carbohydrates. To assess the contribution of each carbohydrate fraction, we looked at the results of more than 200,000 corn silage samples analyzed by the Dairy One Forage Laboratory between 2004 and 2020.
Out of 215,203 samples, average acid detergent fiber (ADF) was 25.4% dry matter (DM). Ranging from 21.5% to 29.3%, it had almost an 8-percentage unit spread (see table). The average neutral detergent fiber (NDF) of 212,887 samples was 43%, ranging from 37.3% to 48.7%. That’s an 11.4-percentage unit spread! What is important to know is how much of that NDF is digestible.
Current research considers 24, 30, or sometimes even 48 hours in vitro NDF digestibility (NDFD) as better predictors of forage digestibility than lignin. Since high-producing cows eat more, and their feed passage rate is accelerated, NDFD at 30 or even 24 hours has been suggested as more adequate to describe the energy available to the cow than 48-hours digestibility.
The average NDFD at 24, 30, and 48 hours was 41.7%, 52.7%, and 62.0%, respectively. The ranges on a dry matter basis were:
- 35.1% to 48.4% for 24 hours
- 47.1% to 58.4% for 30 hours
- 56.5% to 67.5% for 48 hours
Since the spread is larger between NDFD24 (13.3 percentage points) compared to NDF30 (11.3 percentage points) and NDF48 (11 percentage points), and the latter two have almost identical NDFD, we suggest using NDFD30 as a more accurate predictor of digestibility and energy of corn silage in high producing and/or early lactation dairy cows.
Continue reading this article published in Hoard’s Dairyman.
