What Is Line Breeding in Beef Cattle

junho 05, 2022 Postar um comentário

Crossbreeding is the mating of two or more breeds to produce crossbred progeny. Crossbreeding is undertaken to:

Utilise the desired attributes of 2 or more breeds
Produce progeny better suited to target markets while maintaining ecology adaption
Ameliorate productivity quicker in traits which are tiresome to modify within a breed i.due east. environmental adaption, fertility and carcase traits
Accept advantage of the product improvements which ascend from heterosis (hybrid vigour) when breeds are crossed.

Combining the attributes of two or more breeds

The beginning pace is to clearly define the production levels in your current herd for all the economically important traits in your herd.

The next step is to make up one's mind what production levels are needed for each of those economically important traits, to run across the requirements of the market you lot are aiming for.

By looking at where you are and where you need to be, you can make up one's mind the advisable breeding objectives for your herd. Identifying breeding objectives is central to planned cattle breeding. Generally, these objectives can be met either by selecting inside the electric current herd or by introducing new breeds into the herd. The introduction of new breeds merely provides a 'breakthrough leap' in irresolute the genetics of the herd (encounter Breed option). However an ongoing pick plan is yet required to continue to brand genetic improvements.

Taking advantage of heterosis

Heterosis is the production advantage that can be obtained from crossing breeds, or strains, which are genetically various. The new combinations of genetic material tin can lead to production advantages over and above the average of the two parent breeds or strains. To be of economic advantage, the new production levels demand to be above those of either parent strain or breed – otherwise you are better off sticking with the superior parent line.

Heterosis tends to exist greater for traits – such as fettle or fertility traits – which are less likely to answer to conventional selection. For example, the level of heterosis doable for fertility traits is likely to be double that which might be obtained for growth or carcase traits.

Steps in establishing a crossbreeding program

Steps that demand to exist followed in setting up a cantankerous breeding program.

Define your electric current situation in relation to markets, breeds, nutrition, environment and direction.
Define the direction and diet levels it is possible to reach in your environment.
Define what market, or markets, you are aiming for and determine convenance objectives.
Determine which breed types will perform best in relation to your desired product traits.
Set up out a long-term breeding programme – the last crossbreeding system may have up to ten years or more than to accomplish.
Stick to your plan once information technology has been established.

Crossbreeding systems

There are five basic crossbreeding systems available to the commercial beef producer.

Two breed cross

The two breed cross system produces commencement cross, or F1, progeny. In this system, the progeny resulting from the cantankerous of 2 breeds are ordinarily all sold for slaughter or to another commercial breeder. This system is often used in northern New South Wales where at that place are specific F1 sales.

The system is well-nigh useful for situations in which females of a specific breed are well adjusted to a given environment. An example is Bos indicus bred females in n, 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 carcase, feed conversion efficiency and vigour.

Figure 1. Two breed cantankerous occurs where breed A and breed B are two purebreds and the F1 progeny (AB) contains equal parts of the two breeds.

Backcross

In a backcross system, all male calves produced from the first cantankerous are sold for slaughter. Female F1 crossbred progeny are mated to males of one of the parental breeds and all progeny are sold for slaughter. This breeding system takes full advantage of heterosis for maternal traits such equally fertility of the cow, and milking/mothering ability (as the mother expresses 100% of possible heterosis) and half of the possible heterosis for growth.

This approach is near useful where adaptation to a specific surroundings is required from a particular maternal breed simply where characteristics from the other parental breed are desired for carcase or growth traits. The crossbred F1 female would also take satisfactory environmental adaptation.

Continual backcrossing is the arrangement used by producers to upgrade or change from one breed to another without having to buy purebred cows, such as in evolution of Brahman herds in Queensland.

Iii breed cross

3 brood cross requires the input of iii divide breeds. Along similar principles every bit with backcross, all first cross male person progeny are sold. Outset 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.

This system takes advantage of both maternal and private heterosis, and of the complementarity of three breeds. An example would be the a case where the first two breeds are chosen to attain maternal heterosis and adaptation to an surround, while the third breed (terminal sire brood) produces the most acceptable turnoff animals. This employ of the F1 female is more often than not considered to produce the greatest lift in productivity, merely information technology is influenced past the quality of the purebreds maintained to breed the F1 females.

Figure 3. The three breed cross is obtained when all the females from a 2 breed cross are mated to a balderdash of a third, unrelated breed. All the three breed cross progeny are marketed.

Rotational cross

Rotational crossbreeding, sometimes referred to as sequence convenance, is when males of ii or more breeds are mated to crossbred females. Over a number of years, each breed volition have contributed its strengths and weaknesses equally.

Variation seen in the progeny in early years of a rotational crossbreeding program may brand information technology more difficult to consistently see a specific market requirement in this product system. When the breeds used are similar, consistency of operation is less probable 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. One time stabilised after many crosses, with a number of breeds (n) contributing equally, the level of retained heterosis may exist expressed every bit:

(2n–2) / (2n–1)

Rotational crosses express more heterosis than composites which utilize the aforementioned number of breeds. This increased heterosis in rotational systems is a result of close to maximum heterosis beingness achieved in each cross with the purebreed.

All animals in the herd benefit from heterosis for both growth and maternal traits in rotational crossbreeding. When 3 or more than breeds are used, heterosis levels of 86% or greater may be achieved. These compare very favourably with self-replacing concluding cross systems in which just well-nigh half the progeny testify heterosis for growth and only a third of progeny benefit from heterosis in their dam.

In rotational crossbreeding, replacement females are generated for the enterprise from the mating programme. All females are potentially available for selection as replacements, whereas in self replacing terminal cantankerous systems, well-nigh a third of the heifers are non bachelor for pick. This means a reduced possibility for genetic improvement through heifer selection, placing that pressure on balderdash 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

Evolution of a composite or synthetic brood 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 subsequently the initial crosses are made, management requirements are the aforementioned equally for direct breeding. Should a market signal betoken a change to the characteristics of the blended, there is opportunity to change direction past incorporating another breed or crossbreed.

The initial choice of breeds must exist based on those which have desirable traits for a particular environment and for the target market.

The per centum of heterosis increases as more breeds contribute in the initial mating program. While the heterosis will non be as high as that accomplished with a rotational crossbreeding program with the aforementioned number of breeds, the management requirements will be reduced.

Figure v. I unproblematic approach to a composite brood

For case, if at that place are three breeds in a given composite, the amount of retained heterosis would be expected to be (three-ane) ÷ three or ii-thirds or 67%.

Inbreeding is not unremarkably significant when numbers are greater than 200 or 300 breeders. Nevertheless, in smaller herds inbreeding can be a trouble. In the extreme instance where a herd uses only i bull all heterosis is lost after approximately eight generations or 40 years.

Comparison crossbreeding systems

The relationship between the various mating systems, per cent of maximum heterosis retained and percentage increment in weight of calf weaned per cow exposed is shown in the table below.

Table 1. Percent of maximum heterosis expected in progeny

Mating arrangement	Maximum heterosis retained		Superiority over parent breeds
	Individual (%)	Maternal (%)	Increased weight of calf weight weaned / moo-cow exposed (%)	Increased value of calf weight weaned / cow exposed at $1.30/kg liveweight gain (%)
two brood cross
A x B	100	0	8.5	sixteen.50
3 breed cross
(A x B) ten C	100	100	23.3	45
Rotational crosses*
2 breed	33	67	12.7	25
iii breed	86	86	20	twoscore
four breed	93	93	21.7	42
Composite crossbreed
2 breed	50	l	eleven.half-dozen	22.five
three brood	67	67	15.6	30.v
4 brood	75	75	17.v	34
5 breed	80	fourscore	18.six	36
vi breed	83	83	19.three	37.5

*This convenance organization refers to Bos taurus x Bos taurus or Sanga ten Bos taurus crosses after near seven different matings.

Input of purebreeds

All crossbreeding systems crave the continuing input of purebred animals. The numbers of animals required to attain this should non be nether-estimated.

Regular crossing provides stud breeders with a substantial incentive to maintain and improve their straightbred populations, particularly in relation to objective performance criteria.

Further data

Breeding for profit (PDF, 1.37MB)

Source: adapted from 'Breeding for turn a profit', compiled by John Bertram, et al. 2009.

Reviewed and updated by Mick Sullivan, February 2021.

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Source: https://futurebeef.com.au/resources/crossbreeding-systems-for-beef-cattle/

Denny Wheint