The feed value of silage varies as it is moved through the bunker, bag or pile. This is why regular forage analysis is important. However, the accuracy of forage analysis is dependent on two factors:
- The method of sampling, which is the producer’s call. Keep in mind that the sample taken for analysis is very small compared to the harvest volume. Therefore, the method of sampling is crucial for the analysis to be meaningful.
- The method of analysis. Generally speaking, wet chemistry is more accurate than dry near-infrared reflectance (NIR) spectroscopy, which is more accurate than wet NIR.
Here are some tips on how to sample different types of silage for analysis.
Sampling a pile or open bunker
Core samples of the closed bunker or pile will give an early indication of the quality of the silage, but will not reflect what the animals are actually eating. In order to understand the animal’s nutritional intake, it is necessary to analyze the open silo.
- Draw an imaginary ‘W’ on the face of the silage and take nine to 12 samples across the face of the bunker or drive-over pile (See picture). Avoid any moldy areas.
- Samples should be taken as small core samples, 10 cm behind the face of the silo.
- Mix the samples together thoroughly.
- The final sample should be around 0.5 kg. If it is too large, use the quartering method:
- Tip the sample onto a clean surface and mix to ensure homogeneity
- Use a clean board to halve the sample equally. If the piles are approximately 0.5 kg, each carefully place all of one pile material into a clean bag.
- If the sample is still too large, carefully quarter the remaining samples by dividing across the pile at right angles to give four separate piles. Aim to collect one pile of approximately 0.5 kg and carefully add all of the material to a clean plastic bag.
- Roll the bag to remove as much air as possible, using a vacuum sealer if possible.
- Place the sample inside another plastic bag and label clearly.
- Samples should be submitted to the laboratory urgently (do not send on a Friday as this will delay analysis).
Variable bunkers or piles
Some bunkers can vary significantly in their composition during feedout, due to layered forages within the bunker or pile, different cuts of forage or variability in feed value between fields harvested at the same time.
This means that regular feed analysis should be undertaken on forage that is representative of what the animals are being fed at the time in order to ensure a balanced diet and achieve the desired milk output and/or weight gain. When milk output drops, it is always advisable to re-assess the feed value of the forage.
Sampling of bales
Bales should not be stored stacked as the net and wrap around each bale is meant only for the weight and pressure of a single bale.
Stacking of bales leads to changing of shape, displacement of plastic and, ultimately, a different feed value between bales placed at different levels. If space is insufficient, bales should be piled on their ends and a maximum of two high.
To sample bales, take three core samples and homogenize by mixing. Bales from each level of a stack should be sampled.
Silage is a single part of the dairy or beef diet and accurate knowledge of all the components of the ration is important to ensure optimal feeding. To learn more about how to read silage reports see our next article coming in february.