Extension Dairy Professor Jud Heinrichs explains this is accomplished by feeding a nutritionally balanced ration at all times, allowing cows to consume as close to their actual energy requirements as possible and maintaining the physical or roughage characteristics, which we now refer to as feed particle size, required for proper rumen function.
Good feeding management practices must be followed to successfully implement a TMR system and achieve maximum performance from cows.
Forages should be chopped properly before ensiling. Most forage particles in silage and haylage should range from 3/8 to 3/4 inch in length. Forage particles that are very fine, or grain that is too coarse or whole, should be avoided in the ration. Cows generally sort against long particles due to their less palatable nature and sort for finer particles in the ration. This behavior can lead to metabolic problems such as subacute ruminal acidosis (SARA). Cows consuming the finer particles of the ration are reducing their particle size consumption and, in effect, their NDF intake. These sorted diets contain more fermentable carbohydrates and less effective fiber than the formulated ration. Effectively, a sorted TMR is not a balanced TMR, and much of the time, effort, and expense involved in making the TMR is lost when the cow sorts it.
It is imperative to develop rations based on current forage analysis reports. Current recommendations are to take the average of at least two separate and independent forage analyses from the same lab before building a TMR. Make ration adjustments when a change in forage is observed; again, this should be based on more than one sample and forage analysis. The dry matter of ensiled material should also be checked frequently. A change in dry matter can alter the TMR drastically, and these changes usually are more long term and progressive. Accuracy of the scales and mixing system is critical to a TMR system, and a regular maintenance schedule should be planned and carried out.
Determining the actual dry matter intake of cows often helps to indicate problems with forage quality and dry matter content. Cows should be within 5% of the expected dry matter intake. If actual dry matter intake exceeds 5% of the expected, that ration should be reformulated. Extremely low intakes may indicate that forage quality and/or dry matter contents have changed and may be a limiting factor to intake.
The number of animal groups to have in a TMR system is determined by the existing herd size and layout of the barns and loafing areas. An ideal TMR system for an entire farm could have seven main groups: high, medium, and low production lactating cows, far-off and close-up dry cows, and prebreeding and postbreeding heifers. In addition, many herds separate a first-lactation cow group from older cows for all or part of the first lactation. On many farms this group is critical, especially if other cow groups are overcrowded; first lactation cows most often respond well if they are undercrowded in terms of feed bunk and resting space per animal. Depending on farm size, having this many separate groups may be unrealistic, yet larger farms may have multiple pens for each group.
When working with a one- or two-group TMR system, there is less flexibility to formulate rations to meet specific needs. For instance, the lower-producing cows receive the same forage as the higher-producing cows, which may not allow for optimal use of various forages. In a three-group system, low-group cows can usually be fed cheaper forage to reduce costs. Using a one-group TMR system usually results in higher feed costs because more expensive ingredients such as undegradable protein sources, fats, and certain feed additives are fed to cows in later stages of lactation. These cows should be fed a ration with higher levels of forage than a one-group TMR would provide.
Lower producing cows may become over conditioned in a one-group TMR system. Many of the problems of the one-group system can be avoided by using two groups, especially if one of them is fed according to above average group production. Obviously, cow movement and changing social orders within pens is another factor to be considered when deciding the best number of groups for a farm operation. There is no one perfect answer for all systems and some farms will vary the number of TMR groups from year to year to best match other situations and priorities on the farm.
Source – psu.edu