The nutritional value of feed ingredients has traditionally been explained in terms of their energy, fibre, mineral and protein content. These are intrinsic characteristics of the particular feed ingredient that can be measured and these values are then used in feed formulations. In practical reality various feed ingredients interact to produce a biological response but this is usually ignored in modern feed formulations (Hanigan, 2005; Dijkstra et al., 2007).
However, in modern animal nutrition there are many feed ingredients where the energy, fibre, mineral or protein contents are not measurable or not significant. Some examples are antioxidants, enzymes, and organic acids. These feed ingredients do not satisfy a conventional nutrient requirement nevertheless they give a biological response. In practical reality, it is the response to feed ingredients which is important in supporting animal growth and productivity.
Therefore, in modern animal nutrition, fulfilling conventional nutrient requirements is only part of a successful programme. What is more important nowadays is the response to feed ingredients in terms of production level and product composition, excretion of nutrients to the environment, and nutrition related disorders. Response to feed ingredients is the crucial factor in assessing nutritional programmes.
In poultry and pig nutrition for example, enzymes such as amylase, phytase, protease and xylanase have been used as feed ingredients for many years. The beneficial results in terms of animal performance from the addition of enzymes to the feed led to the development of the concept of Effective Energy to explain these effects. An Effective Energy value is ascribed to the feed enzymes. Clearly enzymes have no intrinsic energy content but in a feed mixture they allow better utilisation of feed ingredients and therefore have an Effective Energy value. Phytases release phosphorus from the feed ingredients and therefore allow feed phosphorus levels to be reduced so in reality phytases have an Effective Phosphorus value.
The Effective Energy concept changes feed ingredient evaluation from a requirement to a response. This is of practical significance because it is the response of the animal to the feed ingredient that is the ultimate indicator of nutritional value.
The Effective Energy value of enzymes for use in monogastric nutrition is now well accepted but the concept has not been widely used in ruminant nutrition. Given the complexity of the rumen fermentation processes which ultimately lead to the production of volatile fatty acids (VFA) and microbial protein for the ruminant animal, enzyme supplementation is not a common strategy.
Nevertheless, in ruminant nutrition, practical feed evaluation systems also need to recognise the Effective Energy value of feed ingredients which can integrate feed ingredient interactions, feed intake and the influence of rumen microflora on nutrient availability. The Effective Energy concept is a valuable tool to improve the assessment of feed ingredients for dairy cow nutrition.
The utilization of feed ingredients in ruminants basically depends upon fermentation of plant constituents in the feed. Both the production of microbial cells and the nutritive value of the end-products of the fermentation are of great importance (Isaacson et al., 1975). Energy intake is a primary limitation on milk yield for high producing dairy cows and it is the interaction of feed ingredients with the rumen microflora that determine the efficiency of energy supply to the cow. This is in fact a response system.
Another important factor influencing the Effective Energy intake in dairy cows is the possible effect feed ingredients may have on feed intake. For example, fat in dairy cow rations can inhibit fibre digestion (Allen, 2000) and this is a major loss in feeding value to the cow as fibre is a very significant component of a TMR. Therefore, feeding fats directly or as calcium soaps are likely to reduce the Effective Energy value of the feed even though the theoretical energy value may be increased. There was a consistent reduction in dry matter intake when calcium soaps were fed from 1-8% of dry matter (Allen, 2000; Weiss and Wyatt, 2004).
An illustration of the Effective Energy concept in dairy cows is in the evaluation of a specialised feed ingredient such as Glycal Forte®. This is a calcium and glycerol complex which can modify rumen activity and supply some energy to the cow. As we will show in the next article Glycal Forte®, through its ability to effectively manage the rumen has an Effective Energy far greater than its chemical composition would suggest. This is a perfect example of a feed ingredient which generates a valuable response in the animal by interacting with other feed ingredients.
REFERENCES
Allen, M. S. (2000). Effects of diet on short-term regulation of feed intake by lactating dairy cattle. Journal of Dairy Science, 83: 1598–1624.
Dijkstra, J., Kebreab, E., Mills, J.A.N., Pellikaan, W.F., López, S., Bannink, A. and France, J., 2007. Predicting the profile of nutrients available for absorption: from nutrient requirement to animal response and environmental impact. Animal, 1: 99–111.
Hanigan, M.D., 2005. Quantitative aspects of ruminant splanchnic metabolism as related to predicting animal performance. Animal Science, 80: 23–32.
Isaacson, H. R., Hinds, F. C., Bryant, M. P. and Owens, F. N. (1975). Efficiency of energy utilization by mixed rumen bacteria in continuous culture. Journal of Dairy Science, 58: 1645-1659.
Weiss, W. P. and Wyatt, D. J. (2004). Digestible energy values of diets with different fat supplements when fed to lactating dairy cows. Journal of Dairy Science, 87: 1446–1454.
