When farmers decide to use by-product as a feed for the cows, it is crucial to ensure the quality is up to standard. The main reason why there is variation in terms of nutrient content is because of the differences in variety of grain used for processing, fertility of soil where the crop is grown, manufacturing plant, storage conditions and processing method.
A study has been done to examine the nutrient content of by-product feeds available to California dairy farmers. The results are summarised in Table 1 (DePeters et al., 2000) shown below. The variation in terms of nutrient concentration in the feed is represented as coefficient of variation (CV) and the unit is in percentage. The lower the CV value, the less variation there is for the specific feed. In general, minerals have higher CV compared to other types of feed. There are certain types of by-products that will have higher variation due to the the different processes used in the industry. Some examples are fiber and fat concentrations of hominy feed.
Table 1. Variation in the nutrient content of select by-product feeds.
During the last decade, processing methods used by manufacturers have changed dramatically. These days, the processor is able to remove the primary product (such as starch, oil and so on.), producing by-products that have different nutrient profile compared to those listed in many references. For example, processing methods that used to produce ethanol now produce distillers dried grains with solubles (DDGS) with a different nutrient content than what was available previously.
Processing technology is constantly being improved everyday for the extraction of primary ingredients. Scientists and researchers are also working on decreasing the amount of nutrients such as phosphorus in by-products. This is so that their use in animal feeds will improve the whole-farm nutrient balance and maintain water quality. Some processing technology that researchers are currently working on will allow production of custom by-products for feeding in the future. For these reasons, dairy farmers should always sample each feedstuff on a regular basis to keep track of the variation or any changes in nutrient content that will impact the nutrient content of diet for the cows