Estimated reading time: 8 minutes
There are three key reasons why maize silage is an excellent feed for high-producing livestock: High dry matter production or total biomass yield, high starch percentage, and good fibre digestibility. These points formed the foundation of Dr Bill Mahanna’s presentation during his recent South African roadshow.
Neutral detergent fiber digestibility (NDFD), he said, is a crucial measure of forage quality and energy density. While neutral detergent fiber (NDF) measures the total amount of fibre in a feed, NDFD measures what percentage of that fibre is digestible. Higher NDFD allows for higher dry-matter intake (DMI) and increased energy consumption, because the fibre disappears from the rumen faster.
Dr Mahanna, global nutrition science manager at Pioneer Seeds in the United States, focussed on ten key take‑home messages for producers during his talks.
Take-home message one
His first and perhaps most surprising message was that when selecting silage genetics, you should speak to your agronomist or seed salesperson first, and only then consult your nutritionist. Even better, he said, is to meet them together and include the contractor who will be making your silage.
The most important factors to consider before nutritional traits, are basic agronomic traits such as maturity, stress emergence, drought tolerance, adaptation to high populations, plant height and disease resistance. These traits ensure yield stability and late-season plant health.
The key, he stressed, is late-season plant health.
“Late-season plant health implies maintaining fibre digestibility, yielding more starch and biomass and allowing for a wider, more flexible harvest window. Late-season plant health is influenced by hybrid genetics, the use of fungicides and soil fertility, especially nitrogen fertility.”
Dr Mahanna pointed out that being able to postpone the cutting date of healthy maize plants leads to significant gains. For every 1% increase in silage dry matter (DM), which is about one day, the plants will accumulate between 0,6% and 1% more starch. Converting this to a dry grain equivalent, it could be a gain of about 308kg/ha per day, or 0,67 MT/ha at 35% DM of silage.
Increasing the harvest dry matter (DM) from 32% to 37% by delaying cutting for 5–7 days because the plants remained healthy, can lead to significant gains. According to Dr Mahanna, this can result in approximately 1,556kg/ha of additional dry grain equivalent, 3% more starch, and 3,7t/ha more yield at 35% DM. Although this delay may cause a 1% reduction in fibre digestibility, he noted that this small decrease is not biologically meaningful in the context of the cow’s overall diet.
He stressed that late‑season plant health is critical, as plants affected by late‑season diseases experience a substantial drop in fibre digestibility.
Turning to the nutritional traits to focus in selecting silage genetics, he said that dry matter yield and starch content are the most important. Dry matter yield is influenced not only by grain content, but also by the plant height at the ear.
He explained that when it comes to starch content, grain accounts for close to 50% of silage dry matter and for over 65% of the energy in corn silage. This, however, is influenced significantly by harvest maturity of the kernel – for example, harvesting at one‑third milk line versus three‑quarters milk line can make a significant difference.
It is also notable that fibre digestibility and crude protein are not on the list of most important nutritional traits. It is all about starch.
“Do you realise how much energy a cow expends in a day?” he asked, “A Holstein annually producing 12,700kg of milk at 4,2% fat performs the metabolic equivalent of a human running 16 marathons every single day. So, she needs a lot of energy!”
Take-home message two
Despite the nutritionist’s desire, don’t focus on fibre digestibility when selecting hybrid genetics, but pay lots of attention to the growing environment of the plant.
What determines fibre digestibility? The growing environment during the vegetative stage affects corn plant height, biomass yield and NDFD. Dryer conditions cause shorter plants and higher NDFD. Wet conditions, on the other hand, cause taller plants and lower NDFD. After silking, the growing environment primarily affects grain yield and thus the starch content and energy density of the resulting corn silage.
Two things that destroy NDFD, he said, are excess moisture during the vegetative stage and a lack of plant health close to harvest. What is also very important to bear in mind is that fibre digestibility does not change significantly during storage. Whatever the NDFD was at harvest is what it will be when feeding the silage. Ruminal starch digestibility, however, will increase over time in fermented storage.
Fibre digestibility is also strongly affected by differences in soil type across a field, including factors such as water‑holding capacity and nitrogen profile. These soil‑related variations cause much larger differences in fibre digestibility than the genetic differences between cultivars or hybrids. However, this field‑based variation can be reduced through proper facing and thorough blending of the silage.
According to Dr Mahanna, growing environment is the main influencer of fibre digestibility, not genetics. It has three times more influence on NDFD than genetics.
For this reason, irrigated maize tends to be lower in NDFD. Higher chopping hight might be a good strategy to increase fibre digestibility. Furthermore, the moisture the maize plant receives is seven times more influential on fibre digestibility that heat units.
Take-home message three
Don’t focus on starch digestibility when selecting hybrid genetics.
Take-home message four
Pay close attention to the “farming” side of maize silage production. Tillage practices and planting accuracy is just as important for silage as for grain production. Some of the issues to pay attention to include compaction layers, planter performance (seed to soil contact), planting too shallow resulting in nodal roots not developing properly, and poor planter setup resulting in late emerging plants.
Take-home message five
Plant at proper populations to optimize both starch and biomass yield. A 2017 study examined two standard hybrids across seven different fields at 55 000; 70 000; 85 000; and 100 000 plants per hectare. The study demonstrated that planting density increased yield and, while reducing stalk diameter, did not significantly reduce the 30-hour ruminal in vitroNDFD of the resulting silage.
Lower plant populations do not meaningfully improve fibre digestibility, but they do reduce yield. For example, reducing the population from 70 000 to 55 000 plants per hectare can decrease yield by as much as 1,7 MT/ha.
A key factor to keep in mind is that some hybrids can tolerate the stress of higher planting densities much better than others.
Take-home message six
Do not harvest healthy maize plants too early. Use both kernel maturity and whole‑plant moisture as indicators for the correct harvest time. Harvesting closer to the three‑quarter milk line allows you to capture more starch without causing a significant reduction in fibre digestibility in healthy plants. While NDF digestibility decreases only slightly in well‑maintained plants, their starch content can increase by up to one percentage point per day.
Take-home message seven
During wet growing seasons, consider strategies such as raising the chopping height to improve fibre digestibility. Aim to allocate the silage with the highest NDFD to transition cows and high‑producing cows.
High chopping (increasing the chop height from 17cm to 50cm) is particularly effective in boosting NDFD under wet conditions. Although this method reduces yield, every 15cm increase in chop height results in one percentage point increase in starch content, one percentage point increase in NDFD, but about 2,2t/ha reduction in yield at 30% dry matter.
However, the yield lost is mainly less‑digestible fibre from the lower stalk internodes, not from the leaves, ear, or the more digestible upper stalk portions.
Take-home message eight
Closely monitor chop length and kernel processing at time of harvest.
There is no ideal chop length for maize silage. It depends on the inclusion level of all the other forages in the ration. Maize silage is typically chopped at 19mm to ensure adequate ‘effective’ fibre levels.
Research indicates that particle size seems to influence eating time more than rumination time and suggest maize silage be chopped from 16-22mm and no longer.
Very long particles in the diet will prolong eating time without providing any greater rumination stimulation because cows tend to chew to a relatively uniform particle size (8mm screen on pen state particle size separator) before swallowing.
Kernel processing is a critical factor in producing high-quality silage. This determines how much starch the cows are able to utilise. When chopping at 19-22mm and harvesting more mature kernels to capture more starch, it is important to have the kernels adequately processed or it will end up in the manure.
The best field test to control the efficiency of kernel processing is a one-litre cup. During chopping, fill the cup four times or more a day and inspect the contents. If you see more than two to four half or whole kernels in this volume of silage, chopper adjustments may be called for. The ideal is two whole kernels or less. Between two and four kernels is adequate, but more than four kernels are inadequate.
Historically, processors were set with a roller differential of 10–20% but increasing this to 40–50% significantly improves the processor’s ability to effectively damage kernels.
Take-home message nine
Protect your seed investment with proper ensiling, inoculation, covering and feed-out management. Compaction density and moisture are important to prevent air porosity, which fuels yeast and other spoilage organisms. Use inoculants and proper covering to stop yeast and make sure your face management is first class.
Take-home message ten
Technical help is available from Pioneer’s agronomists and the Pioneer Global Nutritional Sciences Team. – Izak Hofmeyr, Plaas Media
For more information, contact Dr Bill Mahanna at bill.mahanna@pioneer.com or HW Beeken, Pioneer field agronomist for KZN at 082 698 8117.
