For adequate sampling procedure, it is essential to use proper sampling equipment to ensure the collection of a representative sample (Gonçalves et al., 2016).
The most common sampling equipment for bulk feeds or feed ingredients is the slotted grain probe (Figure 1), which can be manual or automated. The slotted grain probe should be long enough to reach the bottom of the bulk carrier to obtain a representative sample from top to bottom. Samples should be collected from at least 10 evenly-spaced locations in the bulk carrier (Figure 2) to be representative of the entire load of feed or feed ingredient (AAFCO, 2017).
Alternatively, a pelican sampler (Figure 3) is also commonly used to steam cut samples during loading or unloading of bulk feeds or feed ingredients. Samples should be collected at least 10 times at regular intervals during loading or unloading (AAFCO, 2017).
In either sampling procedure, the sample size should be at least 1 lb and preferentially 2 lb (AAFCO, 2017).
The sampling equipment for bagged feeds or ingredients is the bag trier (Figure 4). The bag trier should be inserted diagonally in one corner to reach the opposite corner of the bag (Figure 5). At least 10 bags should be collected from the lot, with random selection of bags at varying locations in the lot. The sample size should be at least 1 lb and preferentially 2 lb per bag (AAFCO, 2017).
The sampling procedure of liquid ingredients, such as fats, oils, and amino acids, can be performed from bulk, tanks or barrels, or during unloading. The sampling equipment for liquid ingredients in bulk is the bomb sampler and in tanks or barrels is the drum thief sampler. In both cases, liquid ingredients should be stirred before sampling to ensure a proper distribution of nutrients. At least 500 ml or 1 pint of liquid ingredients should be collected from the container (AAFCO, 2017).
Samples of complete feed are collected from feeders by probe or hand-grab sampling. Samples collected with a probe have less variability and require fewer number of samples (Jones et al., 2018). Samples should be collected from at least 6 feeders with probe and 9 feeders by hand. Approximately 1 to 2 lb of feed should be collected per feeder and mixed in a composite sample. Creating a composite sample by mixing feed from the sampled feeders is recommended to minimize variability and reduce the number of samples for analysis (Jones et al., 2018).
Figure 1. Slotted grain probe (Herrman, 2001)
Figure 2. Sampling locations in bulk carriers (AAFCO, 2017)
Figure 3. Pelican probe (Herrman, 2001)
Figure 4. Bag trier (Herrman, 2001)
Figure 5. Bag sampling technique (AAFCO, 2017)
Preparation of samples for analysis
Sample preparation involves reduction of samples to a suitable size for analysis (Gonçalves et al., 2016). First, composite samples of feeds or ingredients should be mixed thoroughly. Then, samples are split with a riffle divider (Figure 6) or by the quartering method (Figure 7). The process should yield two samples of approximately 500 g or 1 lb each: one to be submitted for analysis and a second one to be retained as a backup (Herrman, 2001).
Samples for analysis should be placed in plastic or paper bags for submission. Plastic bags are conventionally used, but paper bags are preferred for high-moisture or mold-contaminated samples to prevent condensation of moisture and proliferation of mold growth. Samples should be identified with sample number, date, and content (Herrman, 2001). Labels should not be placed within the bag in contact with the sample (AAFCO, 2017).Retained samples should be placed in plastic bags, labeled, and immediately frozen for storage. Retained samples should be kept for a predetermined period of time. Usually, the minimum is until feed is consumed by the animals or as long as potential liability exists, e.g. until marketing (Herrman, 2001).
Figure 7. Quartering method (Herrman, 2001)