Diet formulations

Because of changes in the price and availability of feeds, lot-feeders need to be able to alter the ingredients or ingredient levels in the diet. Demands on feedlot cattle for production and economic performance require that a balanced, nutritious diet be fed. Formulation of the diet depends on the beast’s nutrient requirements for a desired level of performance, the nutrient content of feeds and the price and availability of the feed. Generally, commercial lot-feeders engage a nutritional consultant to formulate diets based on available commodities.

Diets

The majority of cattle feedlots feed high grain diets normally with roughage and with a number of additives fed as a premix. A grain/roughage diet can generally be fed at 75:25 to 80:20, giving satisfactory weight gains at minimum risk, although this ratio can vary from 50:50 to 90:10. After the initial induction into the feedlot, the ration gradually changes, increasing the amount of grain and decreasing the amount of roughage. Currently, nil-roughage feeding systems are rare, but may be used for self feeders. They are generally not recommended.

Starter diets

Roughage has an important role in the introductory period. Grain must be increased slowly and roughage correspondingly decreased so that the gastro-intestinal tract has an opportunity to adapt to the increased grain (starch) content of the diet.

Table 1. A suggested starting program

Processing

In most cases, grains and roughages (hays) need to be processed. Processed grain increases the metabolisable energy (ME) content and, therefore, the liveweight gain and feed conversion efficiency. Processing roughages aids in the handling, mixing and stability of diets.

Formulation

Initially, the ingredients to be used in the feedlot ration must be selected. This depends largely on what lot-feeders have on-hand, the availability of ingredients and current prices.

Secondly, an estimate of the likely inclusion of each ingredient must be made. Normal feedlot rations contain about 4% additives (which are premixed), 10% roughage and 86% grain. Vegetable protein meals may replace some of the grain in the case of low protein grains, especially for young cattle. Molasses can replace some of the grain, which improves the palatability of the diet and reduces dust.

Nutrient content

The nutrient content of the formulated diet needs to be determined and should meet the nutrient requirements for a desired level of cattle performance. The nutrient content of a formulated feedlot diet will be a summation of the nutrient content of each individual ingredient.

Metabolisable energy and crude protein are the major nutrient components of a formulated ration, with mineral and vitamins making up the remaining components of the complete ration. Important minerals and vitamins to consider when formulating a feedlot ration include phosphorus, calcium, sulphur, potassium, sodium, vitamin A and E and other trace elements.

To assess the crude protein level of a formulated ration, specific calculations are made to attain the combined contribution from all ingredients within the ration. These calculations can be computed for all the important nutrients in the diet and these levels then compared to the beast’s requirements for a desired level of performance. Adjustments may need to be made to the ration to exactly meet the requirements.

The general formula for each feed is:

Nutrient contributed = feed nutrient content x % in the diet divided by 100.

Premix ingredients (additives) are usually batched separately in feed bays or silos and then added to the diet. Opportunity lot-feeders usually buy commercial premixed additives which avoids having to mix their own additives. It is important to know the nutrient content of these commercial premixes (sometimes called `concentrates’) to make sure the requirements of cattle are met.

The calcium to phosphorus ratio should range from 1:1 to 2:1 and the urea content should not exceed 1%. Non protein nitrogen (for example, urea) should not make up any more than 33% of the total crude protein in the diet.

The following (Table 2) is an example sorghum based diet, outlining the amount required for each commodity to 1,000kg of ration.

Table 2. Example sorghum diet composition (dry matter basis)

¹Blended oil mix is blend of natural fats, triglycerides, providing the animal with a pure source of metabolisable energy.

The following table further outlines the composition of the sorghum based diet, including the percentage of crude protein content.

Table 3. Calculation of protein (%) in example sorghum diet

Written by Sarah-Jane Forster, formerly Queensland Government.

Further information

Contact the Department of Agriculture and Fisheries Customer Service Centre on 13 25 23, or email info@daf.qld.gov.au.