Energy In, Performance Out
Animals are driven to seek and consume food energy every day – this makes it possible for normal activities, such as growing and walking, to happen. Food energy is also critical in supporting “higher-performance” activities. When athletes engage in rigorous physical activity, their energy needs increase because of the extra work being done by their muscles.
The same is true for “higher-performance” livestock animals, such as dairy cows. As the chart below clearly shows, to allow dairy cows to produce more milk, more food energy (shown as megacalories per day) must be supplied. Also shown is that larger cows require more energy at the same performance level, simply to maintain normal functions.
When considering that food energy is the largest cost of feeding livestock, on an absolute basis, two things become obvious:
- Diets should be formulated to meet, but not exceed, the energy requirement.
- Extracting energy from an ingredient is imperative (considering the economics of doing the extracting, of course).
So far, this all seems fairly simple. However, consider the following:
- Reducing the extrusion temperature by 50oC has been shown to reduce the energy in soybeans available to poultry by about 7%.
- So, processing without quality controls is asking for variation in energy values.
- Experiments with animals to determine energy data are expensive and time-consuming, and so, nutritionists will formulate diets using prediction equations or table values, which may not reflect what is happening in the animal, or what is happening with a process.
- Age of the animal, stage of production, individual animal variation, environmental factors – all affect energy needs and must be considered.
- It must be clear how data is expressed and used – is the moisture content of the ingredient considered (dry matter vs. as-fed basis)? How is the energy value expressed (Gross energy versus metabolizable energy)? What energy use by animals cannot be accounted for accurately, or at all, and how is this uncertainty dealt with?
An example can be seen by going back to the chart on energy requirements of dairy cattle (above), and comparing these predicted energy requirements to published data on actual energy levels in the diet and milk production (Broderick, 2003). The prediction from the chart underestimated energy requirements, from 2.2 megacalories per day (at 69 lbs. milk production per day), to 0.32 megacalories per day (at 81 lbs. milk production per day). In this case, using a prediction energy equation would have limited milk production – although keep in mind that some estimations were used to formulate the diets, too.
In conclusion, using ingredients to supply energy to animals is an art, as well as a science. In the beginning, gather as much information as you can, and then, the animals will tell you a lot once you start feeding them.
See also:Broderick, G.A. 2003. Effect of varying dietary protein and energy levels on the production of lactating dairy cows. J. Dairy Sci. 86:1370-1381.