Cross breeding systems for beef cattle
From Breeding for Profit by John Bertram et.al , Department of Primary Industries and Fisheries
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Cross breeding systems
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There are five basic crossbreeding systems available to the commercial beef producer.
Two breed cross
The two breed cross system produces first cross, or F1, offspring. In this system, the progeny resulting from the cross of two breeds are usually all sold for slaughter or to another commercial breeder. This system is frequently used in northern New South Wales where there are specific F1 sales.
The system is most useful for situations in which females of a specific breed are well adapted to a given environment. An example is Bos indicus bred females in north, central and coastal Queensland. These adapted females can be mated to a sire of another breed, resulting in heterosis for traits such as growth, improved carcass, feed conversion efficiency and vigour. See Figure 1.
Figure 1: Two breed cross occurs where breed A and breed B are two purebreeds and the F1 progeny (AB) contains equal parts of the two breeds.
Backcross
In a backcross system, all male calves produced of the first cross are sold for slaughter. Female F1 crossbred progeny are mated to males of one of the parental breeds and all offspring are sold for slaughter. This breeding system takes full advantage of heterosis for maternal traits such as fertility of the cow, and milking / mothering ability (as the mother expresses 100% of possible heterosis) and half of the possible heterosis for growth. See Figure 2.
Figure 2: The backcross is obtained where all the females from a two breed cross are mated to a purebred bull of either of the original breeds. All the backcross progeny are marketed.
This approach is most useful where adaptation to a specific environment is required from a particular maternal breed but where characteristics from the other parental breed are desired for carcase or growth traits. The crossbred F1 female would also have satisfactory environmental adaptation.
Continual backcrossing is the system used by producers to upgrade or change from one breed to another without having to buy purebred cows, such as in development of Brahman herds in Queensland.
Three breed cross
Three breed cross requires the input of three separate breeds. Along similar principles as with backcross, all first cross male progeny are sold. First cross females are joined with bulls of a third unrelated breed, instead of with one of the parent breeds as in the backcross. All progeny of F1 dams are sold for slaughter. See Figure 3.
This system takes advantage of both maternal and individual heterosis, and of the complementarity of three breeds. An example would be the a case where the first two breeds are chosen to achieve maternal heterosis and adaptation to an environment, while the third breed (terminal sire breed) produces the most acceptable turnoff animals. This use of the F1 female is generally considered to produce the greatest lift in productivity, but it is influenced by the quality of pure breds that are maintained to breed the F1 females.
Figure 3: The three breed cross is obtained when all the females from a two breed cross are mated to a bull of a third, unrelated breed. All the three breed cross progeny are marketed.
Rotational cross
Rotational crossbreeding, sometimes referred to as sequence breeding, is when males of two or more breeds are mated to crossbred females. Over a number of years, each breed will have contributed its strengths and weaknesses equally.
Variation seen in the progeny in early years of a rotational crossbreeding program may make it more difficult to consistently meet a specific market requirement in this production system. When the breeds used are similar, consistency of performance is less likely to be a problem, although levels of heterosis will also be lower if breeds or breed groupings are relatively closely related.
Levels of heterosis achieved in rotational crossbreeding depend on the number of breeds involved. Once stabilised after many crosses, with a number of breeds (n) contributing equally, the level of retained heterosis heterosis may be expressed as:
(2n–2) / (2n–1)
Rotational crosses express more heterosis than composites which use the same number of breeds. This increased heterosis in rotational systems is a result of close to maximum heterosis being achieved in each cross with the purebreed.
All animals in the herd benefit from hybrid vigour for both growth and maternal traits in rotational crossbreeding. When three or more breeds are used, hybrid vigour levels of 86% or greater may be achieved. These compare very favourably with self replacing terminal cross systems in which only about half the progeny show hybrid vigour for growth and only a third of progeny benefit from hybrid vigour in their dam. See Figure 4.
In rotational crossbreeding, replacement females are generated for the enterprise from the mating program. All females are potentially available for selection as replacements, whereas in self replacing terminal cross systems, about a third of the heifers are not available for selection. This means a reduced possibility for genetic improvement through heifer selection, placing that pressure on bull selection.
Figure 4: Starting at 50/50%, the rotation stabilises at 65/35% or 35/65%, giving 65% from the last sire line used.
Because in rotational crossbreeding the mating involves several groups of females of different breed combinations with bulls of different breeds, this system has specific management requirements.
Composite breed
Development of a composite or synthetic breed results from the crossing of two or more existing breeds. There are many examples of this in Queensland: Santa Gertrudis, Droughtmaster, Braford, Charbray, Brangus and Belmont Red.
The primary advantage of forming composite breeds is that after the initial crosses are made, management requirements are the same as for straight breeding. Should a market signal indicate a change to the characteristics of the composite, there is opportunity to change direction by incorporating another breed or crossbreed.
The initial choice of breeds must be based on those which have desirable traits for a particular environment and for the target market.
The percentage of heterosis increases as more breeds contribute in the initial mating program. While the heterosis will not be as high as that achieved with a rotational cross breeding program with the same number of breeds, the management requirements will be reduced.
Figure 5: One simple approach to a composite breed
Heterosis = (number of breeds in the cross - 1) ÷ number of breeds in the composite
For instance, if there are 3 breeds in a given composite, the amount of retained heterosis would be expected to be (3-1) ÷ 3 or 2/3 or 67%.
Inbreeding is not usually significant when numbers are greater than 200 or 300 breeders. However, in smaller herds inbreeding can be a problem. In the extreme case where a herd uses only one bull all heterosis is lost after approximately eight generations or 40 years.
Comparing crossbreeding systems
The relationship between the various mating systems, percent of maximum heterosis retained and percentage increase in weight of calf weaned per cow exposed is shown in Table 1.
Table 1: Percentage of maximum heterosis expected in progeny
Mating system |
Maximum Heterosis retained |
Superiority over parent breeds |
||
|
Individual |
Maternal |
Increased weight of calf weight weaned /cow exposed |
Increased value of calf weight weaned / cow exposed at $1.30 / kg liveweight gain |
|
% |
% |
% |
$ |
2 breed cross: |
|
|
|
|
3 breed cross: |
|
|
|
|
Rotational |
33 |
67 |
12.7 |
25.00 |
Composite crossbreed: |
50 |
50 |
11.6 |
22.50 |
*This breeding system refers to Bos taurus x Bos taurus or Sanga x Bos taurus crosses after about seven (7) different matings.
Input of purebreeds
All crossbreeding systems require the continuing input of purebred animals. Regular crossing provides stud breeders with a substantial incentive to maintain and improve their straightbred populations, particularly in relation to objective performance criteria.
Acknowledgements
Other authors of Breeding for Profit:
Dr Mick Carrick |
Rod Thompson |
Dr Dick Holroyd |
Dr Mick Tierney |
Morris Lake |
Russell Tyler |
Warren Lehman |
Mick Sullivan |
Kay Taylor |
Rick Whittle |
Edited and adapted from Breeding for Profit by Officers of the Department of Primary Industries and Fisheries
Further information
See the Beef Genetic Improvement Project (BGIP) booklets: Breeding for Profit and Bull Selection.
Contact the DPI&F Call Centre on 13 25 23 (Queensland residents) or +61 7 3404 6999 (non-Queensland residents) between 8am and 6pm weekdays, or email callweb@dpi.qld.gov.au
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last reviewed 27 June 2005
