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Plaas Media’s 2021 Santam Agriculture National Silage Competition once again produced interesting data. The competition, which is in its eighth year, boasted a total of 103 entries consisting of 72 maize, 18 oats and seven forage sorghum silages, as well as six silage bales. The latter were entries in a test category and are therefore not included in this discussion.
A dedicated team undertook the mammoth task of sampling and analysing the entries. This team consisted of Plaas Media’s Deidré Louw as logistics co-ordinator, supported by Rochelle George, administrative manager; Richardt Venter of Agsci Unlimited as project co-ordinator; and postgraduate animal science students Gerrit Putter and JG Els from the University of the Free State, Timothy Chilemba from the University of Pretoria, and Henlo Smit from the Stellenbosch University.
Dr Elrisa Taljaard and her expert team at Labworld tested the samples. Prof Robin Meeske of the Western Cape Department of Agriculture’s Outeniqua Research Farm conducted the data analyses.
The composition of the 2021 competition’s maize, oats and forage sorghum silage entries is summarised in Table 1.
Stage of ensiling
The optimum dry matter (DM) content for maize silage is 35%. In previous years many of the maize silage entries were ensiled too early (25 to 30%), which resulted in a reduced yield, lower starch as well as lower energy content.
In the 2021 competition, only 9,7% of the maize silage entries had a DM content of less than 30%. A total of 67% of the maize silages’ dry matter percentage (DM %) was between 30 and 40%. Some good progress has therefore been made with regard to the correct stage of ensiling for maize silage (Figure 1). The DM % of the oats and forage sorghum silages was also spot on.
The crude protein content of the forage sorghum silage was much lower than that of the maize and oats silages. The energy value and starch content of the maize silage, on the other hand, were significantly higher than that of the oats and forage sorghum silages. However, the maize silage’s starch content varied greatly, with the starch content of many maize silages still below 33%.
Grain filling is the biggest determinant of energy value. Producers cannot be satisfied with maize silage that contains less than 30% starch. The fibre content (neutral detergent fibre or NDF %) of maize silage was much lower than that of oats and forage sorghum silage. Attempts should be made to reduce the NDF % of oats silage to below 55%.
The acidity (pH) of silage is one of the most essential and easily measurable properties of silage. All silages had an average pH of below 4, indicative of good preservation. Substandard top-layer preservation and top-layer losses are indicated by an increase in silage pH.
There were several entries of which the pH of the top 10cm was the same as the pH of the sample taken at 20 to 40cm. This is associated with excellent top-layer compaction and sealing of the bunker.
However, the top 10cm of all the entries had a significantly higher pH than the average pH of the silage sample at 20 to 40cm. Top-layer preservation should receive more attention so as to limit losses. If silage deteriorates slightly, the pH will rise.
Lactic acid had the greatest impact on the drop in pH, with levels ranging from 4 to 6% across all silages.
Acetic acid improves the aerobic stability of silage as it inhibits yeasts and fungi. Acetic acid levels of 1 to 2% are sufficient for this. Since acetic acid has a sharp, acidic odour, it can impair silage palatability and intake if acetic acid levels were to rise above 2%.
Butyric acid is the volatile acid that gives silage a rancid smell and taste. It is produced by Clostridia tyrobutyricum which multiplies under anaerobic conditions in silage (for as long as the pH remains above 5,5). Thus, if silage does contain butyric acid, it means that the pH has dropped too slowly during ensiling. A drastic drop in the pH of maize silage from 6 to below 4 usually occurs within 24 to 48 hours. None of the maize silage entries contained any butyric acid.
In contrast, the oats silages in particular contained significant levels of butyric acid. It is therefore a good idea to apply an effective homofermentative inoculant to oats during ensiling. This will ensure that the limited sugars in the oats are efficiently utilised to produce mainly lactic acid.
Exposure stability: Maize silage
Most maize silages were well preserved. However, the aerobic stability of maize silage remains a major challenge. Approximately one-third of the maize silages was unstable after five days of oxygen exposure, and the pH rose by 1. Of the 72 maize silages, 44 were inoculated during ensiling and 28 were not.
Of the maize silages treated with an inoculant, 84% were stable under exposure and 16% unstable. Of the maize silages ensiled without an inoculant, only 29% were stable and 71% unstable. Applying an effective inoculant to maize silage has in many cases improved its aerobic stability.
The easiest way to determine silage stability is to remove some silage from the bunker and verify its pH. Place some of the silage in a bucket with holes in the sides and let it stand for five days. Measure the pH again and if it has risen, for example from 4 to 5 after exposure to oxygen, the silage can be deemed unstable.
Yeasts and fungi feed on lactic acid and sugars, resulting in silage that heats up and a rising pH. In addition to the decrease in nutritional value, silage intake is also impaired, which in turn limits milk production. Another risk is that mycotoxins produced by fungi have an adverse effect on animal health.
An increase of only 0,2 in the pH during oxygen exposure lowers the mark awarded to the silage in the competition. There were quite a few silages that showed no increase in pH after five days of oxygen exposure, and were therefore stable.
Oats and forage sorghum stability
In the oats category there were 18 entries of which 17 were inoculated before being ensiled. Only one oats silage entry was aerobically unstable, although it was also inoculated before being ensiled.
Since the sugars in oats are limited, efficient utilisation of sugars by homofermentative lactic acid bacteria needs to occur for preservation to be successful. Administering a heterofermentative inoculant may impair preservation as it is less efficient at utilising sugars.
If the sugars are depleted before the pH has dropped to an acceptable level, silage preservation will not be sufficient. It is therefore crucial to choose the right type of inoculant to apply to oats during ensiling.
Of the seven forage sorghum silages, six were ensiled using an inoculant, although all the silages were stable after oxygen exposure.
Good compaction is essential to keep oxygen from penetrating the silage bunker. The compaction of maize silage in a bunker should be 240kg DM/m3. The average compaction of the maize silage bunker entries was adequate. However, there were quite a few bunkers that were not as well compacted. Top layer compaction should receive more attention as it can improve on many of the farms.
The compaction of the maize silage in silo bags was only 72% of that of the maize silage bunkers. The compaction of silage in silo bags remains important to keep costs as low as possible and to limit oxygen penetration during silage feed-out.
As always, the aim of the competition is to encourage producers to improve the quality and palatability, as well as the nutritional value of their silage. In addition, it should also be stable when exposed to oxygen. Water and oxygen remain the two biggest enemies of silage and must be excluded at all costs.
The application of a heterofermentative inoculant to maize silage contributes to improved aerobic stability. Oats silage can be improved considerably by increasing the rate at which pH decreases and preservation takes place when applying a homofermentative inoculant.
The nutritional value of the forage sorghum silages was significantly lower than that of the maize silages. Any room for improvement should be fully utilised. – Prof Robin Meeske, Western Cape Department of Agriculture (Outeniqua Research Farm), and Richardt Venter, AgSci Unlimited
For more information, send an email to Prof Robin Meeske at firstname.lastname@example.org.