As I’m writing this at the end of June, some corn is still being planted in the Midwest. There’s been lots of speculation as to what to expect from the late planted crop – much of it dire. The truth is; we won’t know how the Midwest corn will feed until the crop is made. Experts cite that the growing season and timing of a killing frost will determine the outcome.
However, it’s relatively safe to predict that forage will be in short supply on many dairies. I’m acutely aware of the challenges of balancing diets with less than ideal forage supply and lower quality from years of feeding cows in Florida.
FOCUS ON NDF
Remember, cows do not have a forage requirement; they have an NDF requirement. Many diets in Florida are 30 to 40% forage dry matter but still have adequate NDF to keep the rumen healthy and maintain good production and butterfat. We feed more non-forage fiber sources to fill the gap. This includes ingredients like citrus pulp, soyhulls, gluten feed, whole cottonseed, wet brewers and distillers dried grains. It’s not an ideal situation. I’d rather have lots of high quality corn silage and alfalfa, yet it does work.
We also tend to feed higher sugar, lower starch diets, which in my opinion benefits butterfat. These diets take more tweaking and require frequent monitoring of the byproducts. The key is to try to reduce variability and maintain as consistent a TMR as possible.
WEATHER IMPACTS DIGESTIBILITY
I am reading predictions that late planted corn for silage will be higher in NDF digestibility, while others say it will be lower in NDF digestibility and lower in starch. The growing environment is three times more influential on fiber digestibility than the genetics, according to Dr. Fred Owens. The growing environment during the vegetative state is what determines NDF digestibility.
The environment after tasseling will have minimal impact on fiber digestibility, however it will affect starch deposition, according to Dr. Bill Mahanna. Work out of Cornell indicates that the moisture that the plant receives during the vegetative state, coupled with the soil type – sandy versus heavy clay based, is much more influential than temperature on NDF digestibility. Lots of rain will reduce NDF digestibility, while drought conditions tend to increase digestibility.
This goes back to what Dr. VanSoest and Dr. Mertens have been telling us for years. It’s well documented that while irrigation will increase yields, it does reduce fiber digestibility. Starch content will vary, but starch digestibility is less likely to be affected by growing conditions and more affected by kernel maturity at harvest, degree of processing and length of time ensiled.
Our Florida corn silage will vary in 30-hour NDF digestibility from about 50% for corn grown during hot and wet conditions to 60% for corn grown during hot and dry conditions; both low for Midwest standards. However, starch digestibility is similar to what I see in the Midwest, no matter what the growing conditions were.
By the time you read this, you will know what the weather was during the vegetative stage of your corn silage development. This should give you some indication as to how it will feed. Along with tonnage, it will be important to test the corn going into fermentation for NDF digestibility and starch content. Ruminal starch digestibility will improve with fermentation, but fiber digestibility won’t change much. This will give you an indication of how much additional corn and/or byproducts you will need to purchase to fill any gaps in starch or digestible fiber requirements for your herd.