Evaluating Ingredients – Energy for Dairy Cows (TDN vs. NEL) Part 6
In other parts of this blog series, energy has been an important topic. From discussing how dietary fiber and fat levels affect energy in poultry diets, as well as determining how feed form (pellet vs. mash) plays a role, and how the measurements and estimates of energy in each ingredient have to be as accurate as possible. When you want to design a formulation or feeding program, the amount of energy in the diet is always a major concern.
Recently, I wrote a blog with data on required energy in dairy diets (click on the bar graph within the blog) and how important it is to maintain high levels of milk production, to see my point. In short, if you don’t get the energy right, performance will suffer.
While it’s a challenge for all types of animal production, dairy producers have an especially difficult time due to inherent variabilities within the ingredients they use and the complexities of cattle physiology. In addition, many energy systems are used – some proprietary to companies trying to sell them products.
Two of the more common energy systems for dairy are total digestible nutrients (TDN) and net energy of lactation (NEL), both of which can be read about here. Note that TDN has been around longer, while NEL is a more detailed and challenging measurement. NEL can be estimated from TDN, so if someone gives you one of these values, you should question how it was derived.
We can use some data from a research project, designed to change the formulation in order to affect milk production, to compare these methods of energy determination.
First off, the researchers altered the NDF (structural fiber) percentage in various formulations, and this affected milk production in a linear manner:
So, with these different formulations, how did TDN and NEL change?
In this case, NEL is a better predictor of milk production than TDN. However, TDN is better than having nothing at all. In other situations, these relationships will be a little different. Overall, this points to the importance of choosing quality ingredients for dairy rations. This will help alleviate uncertainties associated with dairy formulations.