Opportunity lot feeding of beef cattle, Chapter 6: The feedlot ration
Date: 11 Mar 2004
This document forms Chapter 6 of the publication Opportunity lotfeeding of beef cattle.
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Purpose of the ration
A feedlot ration should be designed to give maximum weight gains and fattening rates at the lowest cost with minimum digestive upset.
Daily feed intake
In many cases, differences in individual feed capacities probably vary more within a group of similar cattle than between different categories.
Most feedlot rations tend to be based on grain, plus dry roughage, with an average dry matter content of around 90%. Therefore, when preparing a budget, calculations can be simplified if you use an intake capacity of 3% of liveweight to calculate the actual weight of feed required. This applies to a ration that is around 90% dry matter.
However, if using a silage or green chop based ration, with an average dry matter less than 80%, or designing a ration to provide energy and crude protein requirements, calculations should be made on a dry matter basis; see 'Dry matter' and Table 6 below, Table 8 in Suitability of feedstuffs, and Table 9 in Buying feed on a feed value basis.
Table 6 provides details of daily feed capacities, metabolisable energy and crude protein requirements on a dry matter basis, for various categories and liveweights of cattle.
Dry matter refers to the amount of dry material in a given feed. Green chop consists of about 15–20% and silage about 30–40% dry matter, while grain is about 90% dry matter. Most feeds used in feedlot rations have a dry matter content of around 90%.
A beast needs between 2.7% and 3.0% of its liveweight as dry matter intake per day. Cattle in low condition may eat 3% of their body weight, while cattle with a high degree of finish have a lower capacity (Table 6).
To find how much to feed, calculate as dry material and divide by the dry matter percentage to get weight. For example, a silage consists of about 30% dry matter. If we need 3 kg of dry matter, then calculate as follows:
3 × (100 ÷ 30) = 10 kg of wet silage
Roughage is required for the satisfactory functioning of the digestive system. Generally, a ration containing 75:25 or 80:20 grain/roughage gives satisfactory weight gain at minimum risk, although rations can vary from 50:50 to 90:10.
The higher the percentage of grain in the ration, the higher weight gain potential, but the risk of digestive upsets is greatly increased when more than 80% grain is fed.
When high levels of roughage are fed — for example, in starter rations — good-quality roughage should be used. Poorer-quality roughages are acceptable when low-roughage high-grain rations are fed.
High-energy rations should be fed for maximum weight gains. Energy is measured as megajoules (MJ) of metabolisable energy (ME) per kilogram of feed.
For efficient fast-fattening, steers under 12 months of age need a ration containing about 12 MJ/kg, and yearling cattle require a ration containing about 11 MJ/ kg. Grains are rich in ME (about 13 MJ/kg) and stubbles are low (about 5 MJ/kg).
Protein is measured as crude protein (CP). Protein is essential for the health, growth and appetite of the animal. Young cattle require higher levels of protein than older cattle. A range of CP from 11% to 15%, depending on age and weight, will be required (see Table 6).
Table 6 Feed requirements of lotfed cattle
|Type||Liveweight (kg)||Daily dry matter % of liveweight||ME (MJ/kg)||CP % in ration||Daily weight gain|
Where a high proportion of grain is fed and the roughage is of good quality, there is often adequate protein in the ration. If not, the addition of 1% urea will effectively boost the protein level and aid digestion.
Rations for young cattle might be low in protein. If so, you can add a high-protein meal such as sunflower meal, linseed meal or cottonseed meal. Because young cattle require a high proportion of their protein intake from true proteins, these protein meals must be used in preference to urea to raise the protein level of the ration.
As cattle slow their growth and become more finished, intake capacity often eases slightly. Weight gain may also ease as more of the energy consumed is converted into fat (higher energy content) rather than muscle.
The preferred minimum entry weight for feedlot cattle is 250 kg (liveweight). Cattle can go on to the feedlot at lighter weights, but their protein requirements are so high that the ration becomes expensive and the time on feed is extended to achieve a marketable (although often not profitable) weight.
Other components of the feedlot ration include minerals, vitamins, salt, non-protein nitrogen and rumen modifiers.
Cattle need minerals to maintain good health. The most important are phosphorus and calcium. Grain is high in phosphorus and low in calcium, so with a high-grain ration, add calcium as ground limestone at a rate of about 1% (10 kg limestone/tonne) of the ration. This amount can be halved when lucerne hay is used as the roughage component.
Extra phosphorus is sometimes added to weaner rations, usually at the rate of 0.1% (1 kg/tonne). Sulfur is often added to rations that include urea, while zinc and cobalt often improve the action of rumen micro-organisms.
Other minerals could be needed, but deficiencies are unlikely to occur in short feeding periods (less than 100 days).
Salt is added at the rate of 0.2% (2 kg/tonne) of the ration to supply the recommended daily allowance for sodium of 0.08% (0.8 kg/tonne).
Non-protein nitrogen (NPN)
Urea is cheap and physically easy to feed. However, it is toxic in excess, and inexperienced operators should not attempt to use more than 1% in their ration. See 'Urea poisoning' in Cattle health in feedlots.
Feed at 1% by weight of the total ration. Because urea can be toxic if fed to excess, take care that this amount does not exceed 2% and that it is thoroughly mixed in the ration. Introduce it gradually, starting with 0.5% by weight (5 kg/tonne) of the total ration for the first 5 days.