Dairy cow ration balancing has become much more precise in the last 15 years with advances in nutrition research, ration formulation models and feed analysis methodologies. Once common terminology like crude protein and net energy of lactation are giving way to amino acids, ruminal neutral detergent fiber, starch digestibility and specific fatty acids.

Essential amino acids
    Dairy cows do not have CP requirements; they have amino acid requirements. Amino acids are the building blocks of proteins. Research and field experience have confirmed that when cows absorb essential AA in a profile that closely resembles the profile their bodies require, total essential AA requirements are reduced and protein utilization efficiency is maximized. Therefore, balancing rations for AA has allowed nutritionists to significantly reduce the amount of CP fed. Increased efficiency of protein utilization and lower CP in rations results in less waste nitrogen to the environment.
    The first goal of balancing a ration for AA is to provide enough rumen-degradable protein to maximize the efficiency of microbial protein synthesis in the rumen. The second goal is to balance rumen-undegradable protein, including bypass methionine and lysine sources, to optimize metabolizable protein, which is the true protein absorbed in the intestine. Microbial protein synthesized in the rumen, together with rumen-undegradable protein, comprise the majority of the metabolizable protein passage to the intestine. Concentrations of lysine and methionine in metabolizable protein have a great impact on protein content of milk and milk yield.

Fiber digestibility
    Dry matter intake has a huge impact on diet digestibility and, therefore, on the energy concentration of the diet. Digestible NDF and starch are the major contributors to dietary energy for lactating cows. Research in the past few years has shown that uNDF (the highly indigestible fraction of NDF) is a more robust predictor of feed digestibility than lignin. uNDF has also become a useful tool to benchmark forages in terms of potential rumen fill and DMI constraints. The difference between total NDF and the uNDF content of a ration is the amount of fiber that has the potential to be fermented in the rumen and turned into energy available to the cow. The extent of ruminal NDF degradation will be determined by the rates of digestion and passage.

Starch digestibility
    Dairy cows are fed significant quantities of starch because it is highly digestible and energy-dense. Although cows do not have a requirement for starch, it is often a key nutrient to maximize production. Some nutrition models now rely on the rate of starch digestibility (starch kd) or seven-hour in vitro starch degradability measured by commercial labs to predict the rate and extent of starch digestion. Physical and chemical factors that affect starch digestibility include type of endosperm, particle size, kernel processing, storage method, moisture content and length of fermentation.

Specific fatty acids
    Fat is another important energy source for dairy cows. As with CP, we have seen a move away from relying exclusively on the total fat content of the ration. Instead, the focus has shifted to feeding dairy cows specific FA. The composition of the fat, especially its unsaturated FA content, can have profound effects on rumen fermentation and production responses. Under certain dietary conditions, unsaturated FA can form unique intermediates in the rumen that are potent inhibitors of milkfat synthesis.
    Rumen unsaturated FA load is one tool currently used in ration formulation to help determine how much fat can be fed to lactating cows. In addition, ratios and blends of specific FA are now being evaluated.

Listen to the cows
    No doubt, feeding high-producing cows has become more precise and sophisticated with today’s tools. It has been said three rations can be delivered to dairy cows: the ration the nutritionist balances, the ration the feeder mixes for the cows, and the ration the cow may sort through and decide to eat. Work with your nutritionist and feed team to read the cows, make sure the right feed is delivered to the right group of cows in a timely and consistent manner, and strive to achieve a good-quality forage program as well as promote excellent cow comfort and management. Ultimately, the cows let us know if the ration is optimal, not the computer.
    Barry Visser is a nutritionist for Vita Plus.