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Balancing Rations for Dairy Cattle

08 October 2012

When balancing rations for dairy cattle, several input variables are important for predicting the nutrient requirements and the predicted outcome of the diet, writes Shane Gadberry from the University of Arkansas.

Minimal factors necessary to predict the nutrient requirements of the cows being milked include:

  • Stage of production and average days in milk
  • Body weight
  • Milk yield

The intake of dairy cows is primarily predicted from body weight; however, actual intake should be used when available.

Once nutrient requirements are established, those values are balanced against the nutrient composition of available feedstuffs. Many dairies rely on hay, silage and byproduct feedstuffs for meeting nutritional requirements. For many, this is where the greatest error occurs in feed formulation and management. Forages are quite variable in nutrient composition. Corn silage in Arkansas has a normal range (mean ± 1 standard deviation) of 57 to 72 percent total digestible nutrients, and this normal range makes up 68 percent of the samples analyzed. Book values can lead to overestimation of energy, resulting in cattle not performing as expected, or underestimation of energy, creating inadequate levels of dietary fiber. Too often, dairy producers want to blame the mixed feed portion of the diet and the feed mill for poor milk production, but they themselves haven’t taken the time to have their forages analyzed for nutrient composition.

With the drought of 2012, some dairies may look to alternative roughage sources, such as crop residues. Crop residues will often be lower in protein and energy compared to average quality Arkansas hay. Use of these residues will be limited to avoid negatively affecting milk production. The limited inclusion rate may result in these alternative roughage sources being difficult to store and blend. More importantly, crops are treated with pesticides, and some pesticides state on the label “do not feed to livestock” or something similar. Other labels may have a time restriction between application and haying or grazing. It is important to visit with the farmer offering the crop residue to find out chemical applications and use restrictions.

Another important aspect in diet management is moisture analysis of feeds, especially high-moisture feeds such as silage and wet brewer’s or distiller’s grains. Error in moisture results in formulation error. If the silage is actually drier than the formulated dry matter content, energy may be less than predicted and fiber greater than predicted; however, if silage is wetter, reduced fiber and higher energy may result. Wet feeds need to be sampled and stored in a manner that minimizes evaporative moisture losses between sampling and lab analysis. Arkansas corn silage dry matter content has a normal range of 26 to 49 percent with an average of 38 percent. By comparison, the Dairy One database for corn silage averages 34 percent dry matter with a normal range of 24 to 44 percent.

Forage and silage samples can be analyzed through the University of Arkansas Agricultural Diagnostics Laboratory. Samples are submitted through the local county Extension office. The lab is also capable of testing grains for feed value. For other feedstuff and diet analysis such as byproduct feeds, oil seeds or total mixed ration analysis, commercial labs such as Dairy One, Dairyland or SDK are better options.

Today’s ration evaluation software programs go beyond balancing nutrient inputs against the requirements for the cow. By including milk price and feed costs, these programs calculate feed cost per unit of milk and income over feed costs. This tool is helpful at examining different ingredients and their costs to target least-cost milk production. Software programs also calculate fecal and urinary output of nitrogen and phosphorus for nutrient management considerations.

In addition to formulating for protein, energy, mineral and vitamin requirements, rations may also be fortified with specialized fats, ionophores, buffers, yeasts and other rumen environment modifiers and anionic salts for milk fever management. The best information pertaining to these products will be based on unbiased university research. If an additive doesn’t result in significant improvements in reproductive rates, milk production or feed conversion, there is likely no economic benefit.

While it is common for feed companies to provide consulting nutrition work, the University of Arkansas Animal Science Department can also assist with diet evaluation. The Spartan Dairy 3 program is currently being used by Dr. Shane Gadberry, Animal Science Extension, to assist with dairy diet evaluation. Contact your local county Extension office if you need assistance in this area or need recommendations on feedstuff testing and test results interpretation.

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