The mechanics of profitable dairying
A lot of information is available on everyday roughages such as maize silage. Optimum cutting times and ways of ensuring the best quality have been well researched and documented. However, there are a few roughage sources in South Africa about which much less is known, although they are a vital part of the dairy unit in certain regions. Small grain silage is a roughage source that is readily available and widely used in large parts of the Western Cape. Small grain, mainly include oats and barley, is often key to success in this area.
Editorial as published in The Dairy Mail – October 2017
We need to understand that although small grain silage has a lot in common with other silage types, not all rules apply. For the purposes of this article, results of 93 samples of grain silage from the Cape region were pooled. Samples were analysed using LaboExpert in association with BLGG, a world-renowned roughage research company. Data were not statistically analysed for this purpose, but trends emerged that point to the important issues. Small grain silage has a lot in common with other silage types, but the rules differ.
The influence of starch content
Starch content is important in maize silage. Increasing the starch content has a virtually direct influence on the energy of the total roughage, mainly because of the large quantities involved. Maize silage starch levels can easily exceed of 35%. This does not apply to small grain silage, where the starch content does not usually exceed 8%.
In the sample pool used, only 17% of small grain silages analysed had a starch content higher than 8%. Because of the lower starch content, the total energy supplied by small grain silage is much lower. Therefore, unlike in the case of maize silage, starch content should not be one of the main determinants of the correct time to harvest.
Figure 1 The influence of starch content on energy level of small grain silage
Figure 1 shows the relationship between starch and energy, and although there is a relationship, it is very small. It should be pointed out that the handful of silages with a starch content above 8% did all have above-average energy levels. Nevertheless, the same level of energy was obtained with lower starch levels as well, owing to various other factors. So, that leads us to ask: What are the other drivers of higher energy small grain silages?
Using dry matter content of the crop to determine time to cut could be relevant, but choosing the best cutting time on the basis of silage samples does not work, as the norm is to cut the crop and let it lie for a time period before ensiling it. In maize silage this is not done so using DM content to determine best time to cut is relevant there. This lag period in small grain silages skews any relationship based on dry matter and using this as an indicator here would produce the wrong results.
As in the case of maize silage, the digestible organic matter content of the roughage does seem to have a huge impact on the energy available to the animals from small grain silage. The close relationship between the digestible organic matter and the energy available from the roughage as indicated in Figure 2 clearly proves the importance of doing everything possible to improve the digestible organic matter content small grain silage.
Figure 2 The relationship between Digestible organic matter and energy available from roughage.
There are several factors that do result in a higher digestible organic matter. Of these probably the fibre content of the roughage is one of the biggest role players. The relationship between digestible organic matter and crude fibre content and although not as strong as the relationship between digestible organic matter and energy, there is still a fairly visible inverse correlation. This indicates that by decreasing the crude fibre levels of your small grain silage you will increase the digestible organic matter and thus increase the overall energy content of your silage.
One could also argue that increasing starch would increase the digestible organic matter of small grain silage, and this would be true if the starch percentage were much higher. But at the low general levels of starch in these silages, increasing starch has little effect on improving digestible organic matter and energy, as previously pointed out.
The best approach
So, what is best approach to making small grain silage? Decreasing indigestible fibre would be key. This means cutting the crop at a younger stage and not necessarily waiting for starch levels to increase. Waiting for higher starch levels will increase the maturity of the plants and again lead to lower digestibility after a certain point. Cutting at a younger stage does mean less available starch but significantly decreases the fibre and indigestible fraction of the plant. The benefits of a more digestible product are higher energy available for milk production, the need less concentrate feed, higher yields and better cow health. An additional benefit to cutting at a less mature state is improved crude protein content of the silage. The negative aspect of cutting at a younger stage is reduced tonnage. This could however, be turned to good account if done correctly under irrigation, as cutting young enough could stimulate regrowth, leading to increased tonnage. Farmers should take care when cutting younger crops not to ensile when the product is too wet as this can make it difficult to preserve the silage. Good ensiling practice should still be applied and the dry matter target in the final product should be between 30% and 35%.
Profitable dairying is the main consideration and if small grain silage is a large part of your business unit then it should be important to you to take all factors in consideration.
