The following article discusses research conducted at the Prairie Swine Centre and on a commercial farm evaluating the impact of feeding diets with increasing digestible energy content. Although we can estimate the energy content of the diets using published values for each ingredient we have based our results on the DE content which we measured. This involves determining the caloric content of the feed in a lab and measuring feed intake in the barn. We also must determine caloric output, – collecting faeces and determining the caloric content of what is excreted. Although this may sound like fun, it is actually quite time-consuming and expensive, – so why don’t we just use the published values?
The following graphs show data from several digestibility experiments. The top graph is from grow-finish experiments. If the measured values equaled the formulated, then the data would follow the line. The difference between the formulated and the measured ranged from 17 kcal to 175 kcal. This can be a significant difference, however, the difference appears random, and therefore, using the measured values would not bias our results in one direction. Conversely, as can be seen in the lower graph, when weanling pigs are used, not only are the measured different from the formulated, but the measured is always less, therefore, if we didn’t actually measure digestibility our estimated values would not only be variable, but would be consistently too high.
The variability in the diet DE content observed in both the grower and weanling pigs is due to the natural variability in the DE content of various grains (ie. see COS ). The bias observed with the weanling pigs is because published DE values are based on grower pigs. Because of anatomical and development differences, digestibility in the younger pigs is always lower.
As can be seen in the following article, a difference in DE content of only 100 kcal can significantly impact feed costs and net returns. Therefore our research will continue to be based on actual, rather than formulated DE values, and collecting and grinding faeces will be part of our day!