There is extensive research to demonstrate the benefit of nutrient absorption enhancers in traditional broiler diets with moderate to high levels of added fat. The enhanced digestion and absorption of nutrients has been widely shown to allow substantial diet reformulation and offer significant feed cost savings. However, increasingly we are seeing the use of diets with little, or no added oil are becoming more common, so what is the benefit of nutrient absorption enhancers in diets without added fat?
Chickens subject to heat stress, must preserve a thermal balance between their internal metabolic heat production and body heat loss to the environment. Only if the core body temperature of the bird remains under control, can optimum growth and feed conversion be achieved. The heat production of birds depends on the digestion of feed. Feeding an optimal digestible ration requires significantly less energy for the birds to digest and utilise, compared to that of a poorly digestible formulation. Additionally, the digestion of certain nutrients generates less body heat (heat increment) than others. For example, lipids produce significantly less heat per calorie of feed energy while being digested, compared to proteins. Additionally, protein turnover accounts for 9 to 12% of basal energy expenditure whereas in contrast, fat turnover only accounts for 2 to 4% because of its lower turnover rate (Baldwin et al., 1980). Hence, increasing the fat content of the diet (whilst maintaining the same total dietary energy level) helps to reduce body heat produced.
Table 1 – Energy values of starch, crude protein, and crude fat according to energy systems and generation of body heat (Noblet, J. and Van Milgen, J., 2004.)
In parenthesis, energy values as percentage of starch. Crude protein and crude fat are assumed to be 90 % digestible; the starch is 100 % digestible.
Therefore, it is necessary to adjust the feed formulation during heat stress, to ensure maximum digestibility and optimal supply of all essential nutrients, controlling the incremental heat production, ultimately providing the best support for maximum bird performance.
