Feeding Management on TMR Systems
Posted: June 17, 2015
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 it is sorted by the cow.
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. The larger the farm, the easier it is to have the larger number of groupings or ration changes throughout the lactation cycle.
Dry cows, in particular, are often recommended to be divided into two groups, far-off and close-up. Using a two-group TMR system for dry cows can minimize the level of metabolic and nutritional disorders observed at calving and in the postpartum period. The close-up group should be cows two or three weeks from calving, or if it is being balanced for anions and cations, three to four weeks.
To ensure proper ration formulation for growth and development, a two-group TMR system is necessary for heifers with the inclusion of one prebreeding and one postbreeding heifer group. Young heifers lack the capacity to consume very high forage diets while maintaining proper growth. It is necessary for prebreeding heifers to have an energy- and protein-dense diet.
There are other points to consider when feeding a TMR. First, the ration should be available to the cows 22 to 24 hours daily. To promote maximum feed intake it is often recommended that refusals for the fresh group remain around 2 to 4%, 1 to 3% for high groups, and 0.5 to 3% for late-lactation groups. In general, feed refusal should not exceed 3 to 4%. Feed refusals can be fed to older heifers, steers, or other beef cattle. Refusals should never be fed to prefresh or fresh cows. First-calf heifers should be placed into a higher group than their production level to compensate for growth that they will have in the first lactation. Placing first-lactation heifers in a group separate from older cows reduces competition and gives younger cows improved access to bunk and stall space. Second, if hay or grain is fed separate from the TMR, it should be limited to two to five pounds per head per day. Supplemental grain feeding to high producers may be necessary in one-group TMR systems. However, the amounts to feed will depend on the level of concentrate that is being fed in the TMR. When large quantities of feedstuffs are fed separately from the TMR, the TMR loses many of the advantages it has over conventionally fed rations. Therefore, if possible keep all or nearly all of the ingredients in the TMR to maximize performance and profit.
An excerpt from the Penn State Extension publication Total Mixed Rations for Dairy Cows: Advantages, Disadvantages, and Feeding Management.