Two-breed terminal
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The two-breed terminal system is the most basic crossbreeding system.
This system crosses Breed A females with Breed T sires to produce a crossbred animal that is 50% Breed A and 50% Breed T and is known as an F1.
The crossing of two well-bred pure breeds is done to attain maximum hybrid vigour in slaughter animals. The greatest advantage of this system is the complementary effect of the breeds on each other. One pure breed cow and two bull breeds, viz. one for pure-breeding and one for crossbreeding are required. All offspring are marketed.
- The system is simplistic
- Only one breeding herd is required or needed
- Labour and management are minimised
- Progeny are highly uniform and marketable
- Replacement heifers are purchased (marketed?), which frees up labour, land, and other resources to be dedicated to other aspects of production
- This programme is appropriate for herds of all sizes because only one sire breed is used; just one breeding pasture is needed, and replacement females are purchased
Three-breed terminal
The three-breed Terminal System is merely identical to the two-breed rotational system. The only difference is that the females are crossbreds (A x B) mated with breed T bull.
Advantages of the Three-breed Terminal system:
- Only one breeding pasture is needed
- Sire identification of breeding females is easily recognized.
- Replacement females are purchased, and all calves are marketed
- Because replacement heifers are not being produced, sires can be chosen only on growth and carcass with no attention to maternal traits
- The system works for herds of all sizes
- The system results in the most hybrid vigour of any crossbreeding scheme
- This system results in 100% percent of both individual and maternal heterosis over the average of the parent breeds, which results in an increase of 24% in weight of calf weaned per cow exposed.
Three-breed Terminal system
A reliable source of quality and the same type of replacement heifers is a necessity. The age of heifers is very important regarding their puberty and readiness to mate when purchased. The cost of these replacement heifers is an important factor in the economy of this system.
Two-breed rotation
Two-breed rotation is an effective and relatively simple crossbreeding system that takes advantage of individual and maternal heterosis.
In this system, females sired by Breed A are mated to sires of Breed B, and females sired by Breed B are mated to sires of Breed A. This system requires two breeding herds and the identification of a sire for each breeding female.
Two-breed rotational system
Two bull breeds are used on two-crossbred cowherds as shown above. It is important to note that the cows in each herd as well as the bulls denoted to them remain in the same herd for their full productive life. Only heifers get transferred to alternative herds. This system is simple and easy to manage.
The identification of breeding animals can easily be managed with an ear-tagging system, through different colours and numbers for the breeding herds. The replacement heifers mated by Breeds A and B are retained. The hybrid vigour will stabilise at 67% of potential and direct heterosis with an expected 16% increase in weaner weight, after several generations.
Some considerations for the breeder:
- Resources available to raise replacement heifers, and the size of the cowherd
- Biological type is significant because females are being retained that are sired by both Breeds A and B
- Both breeds should have maternal characteristics conducive to utilisation as commercial females
- Replacement heifers are retained in this system, which requires additional land, labour, and resources
- The cost and availability of these resources need to be considered.
- Two-breed rotation requires at least one bull from each breed. Each bull is used to service 25 females annually and therefore a herd will need at least 50 breeding-age females for the system to be efficient
- The two-breed rotation can be used with fewer cows; however, bull expenses per cow will be greater
Three-breed rotation
The three-breed rotation is very similar to the two-breed rotation, except that another breed is added. This rotation uses sires of Breeds A, B, and C.
Breed A sires are mated to females sired by Breed B, Breed B sires are mated to females sired by Breed C, and Breed C sires are mated to females sired by Breed A. Replacements are retained from within the herd, and three breeding pastures are needed.
Three-breed rotational system
Advantages of the three-breed rotation system
- The primary benefit of a three-breed rotation over a two-breed rotation is the increase in hybrid vigour
- In a three-breed rotation, hybrid vigour stabilizes at 86% of potential individual and maternal hybrid vigour, and a 20% increase in weight of calf weaning weight per cow exposed over the average of the parent breeds is realized.
Disadvantages of the three-breed rotation system
- An additional (3rd) breeding pasture and breed of bull(s) must be maintained
- Management and labour requirements increase because of the additional complexity of using three breeds over two
As in the two-breed rotation, the three breeds used should be complementary, with maternal characteristics conducive to the breeding females’ role in a commercial herd.
Using the previous example of 25 cows per bull with three breeds of bulls, at least 75 breeding age females are needed to be efficient. The three-breed rotation can be used with fewer cows; however, bull expenses per cow will be greater. Lastly, the ability to locate three breeds that fit a given breeding scheme can be challenging and limit the ability to readily use three breeds.
Four breed rotation
Four-breed rotational system
The four-breed rotation is like the other rotation systems, only with four breeds of bulls utilised.
Breed A sires are mated to females sired by Breed B, Breed B sires are mated to females’ sire by Breed C, Breed C sires are mated to females sired by Breed D, and Breed D sires are mated to females sired by Breed A.
Replacements are retained from within the herd, four breeding pastures are used, and four breeds of sires must be maintained.
In a four-breed rotation, hybrid vigour stabilizes at 93% of potential individual and maternal hybrid vigour, and a 22% increase in weight of calf weaning weight per cow exposed over the average of the parent breeds is observed. This is only a slight gain from the three-breed rotation with the added cost of labour, management, and another breed of sire.
Depending upon the circumstances of the operation, the benefits may not outweigh the cost of using a four-breed rotation in place of a three-breed rotation. Also, assuming 25 breeding-age females per sire, at least 100 breeding-age females are needed for this system to be efficient.
Three-breed Roto terminal
A three-breed roto terminal system is an extension of the two-breed rotational system. It is also known as a two-breed rotation with a terminal bull system. A percentage of the breeding females are placed in the two-breed rotation, and another percentage is mated to a terminal bull C.
For example, 50 percent of herd females are in the two-breed rotation, and 50 percent are mated to a terminal sire of Breed C. The females in the two-breed rotation produce the replacement heifers, and the females in the terminal cross produce all market calves.
The roto terminal system is essentially a hybrid crossbreeding program using aspects of a terminal program and a rotational program. This system allows the breeder to produce all own replacements while making greater use of hybrid vigour in the terminal calves. Terminal sires can be selected for increased growth and carcass traits to maximize production from the cowherd. The breeds used in the two-breed rotation must still be selected for the criteria specified in the rotational programs. The downsides are that more labour, management, and breeding pastures are needed than in a two-breed rotation.
Three-breed roto terminal systemBull Rotation
Bull rotation is a common crossbreeding system. One breed of bull is used for 4 to 6 years, and then the bull breed is changed. This system can use two or more breeds depending on the goals of the producer.
This system is simple in that only one breeding pasture is used, and only one breed of bull is maintained. A relatively high level of heterosis is maintained, usually 50% or greater depending on the number of bulls used and the sequence in which bull breeds are used. Small producers often use this programme because only one breed of the sire is needed at a time.
Bull rotation crossbreeding system using two breed
Bull rotation crossbreeding system using three breeds
The biggest concern when using bull rotation is inbreeding. If a bull’s daughters are retained as replacements, action needs to be taken to prevent inbreeding. This often means replacing the herd bull or adding breeding pastures and separating females from their bulls.