What do the letters TDN stand for when evaluating a dairy ration?

The correct answer is Total Digestible Nutrients, commonly abbreviated as TDN. This term is crucial in evaluating the nutritional value of a dairy ration because it represents the sum of all the digestible nutrients in the feed, expressed as a percentage of the total feed intake on a dry matter basis.

TDN encompasses the digestible fiber, protein, carbohydrates, and fats within the feed, providing a comprehensive measure of the energy available from that feed for the dairy cattle. This information is essential for formulating balanced diets that meet the energy requirements for maintenance, growth, and milk production in dairy cattle. Using TDN allows nutritionists and farmers to assess whether feed offers sufficient energy to support the animals' health and productivity.

Other terms such as Total Daily Nutrition, Transportable Dairy Nutrients, and Total Dietary Needs do not reflect the industry-standard terminology used in evaluating energy content in dairy rations and therefore do not accurately represent the concept of nutrient digestibility as TDN does.