Guidelines for selecting the breeding system

Consider selection of the best  genotype for your enterprise as part of setting the enterprise direction (refer to Procedure 1 of Module 1: Setting directions.

Assess merits of a change in breed or crossbreeding compared to within-breed selection only.

Evaluate the merits of changing breeds, crossbreeding or within-breed selection alone. In general, the genetic variation within breeds is large and will allow many breeds to compete in a range of markets, so the decision about whether to move to an alternative breed or cross will be based on an assessment of whether the size of the changes needed in the traits of your current herd is so great that it will take too long to achieve by simply selecting better bulls within your existing breed and/or source of bulls. 

It is important to calculate the costs, time and effort required to implement a new breeding system to ensure that the advantages outweigh the difficulties.

Changing breeds may cause large changes in some traits and may change the relativity between traits such that a decision to change breeds will require refining the breeding objective and calculating a customised selection index using BreedObject^TM.

Options include:

• Replacing the existing herd by buying in an alternative breed. This is the quickest method, but also the most costly. Embryo transfer is also an option, although this may be cost prohibitive for most commercial operations.
• Building up to the desired breed or combination by crossing with bulls from the chosen breeds. This option is slower, but will generally be less costly and brings with it the complementary hybrid vigour that comes from crossing genotypes during the transition to the new breed or breed combination.
• Building up by buying in replacement heifers of the desired breed/cross breed. This strategy can be applied when/if restocking after drought or other significant destocking events, or more slowly each year to simply replace cull cows and mortalities.

Although ongoing advantages can be achieved by implementing a planned crossbreeding program, you also need to consider the potential disadvantages, such as:

• additional herd management associated with crossbreeding
• discounts that might be experienced when selling crossbred animals, particularly for some breeds when sold through the saleyard system or to specialised markets that specify breed composition
• time and cost required to bring the herd into ‘equilibrium’

Crossbreeding is better suited to larger herds, with more bulls and bigger lines of cattle for sale but could be a good option for smaller herds to utilise some hybrid vigour and optimise breed combinations.

After deciding on breed and whether to crossbreed, further genetic progress relies on selection of replacement bulls within the available genotypes. This is discussed in Procedure 3.

What to measure and when

Consider a change in genotype when:

• potential genetic improvement, of traits that are economically important, within breed isn’t adequate to make the changes you need for your program
• potential for marginal return on investment for an alternative breed is greater than for other investment options
• cash flow during the transition period to the new breed or cross can be maintained at acceptable levels
• before significant restocking events.

This is a strategic decision. The measures that are needed for an economic evaluation of options are described in Module 1: Setting directions.

Advantages and considerations for crossbreeding

Planned and well managed crossbreeding systems will deliver significant benefits to beef producers through hybrid vigour. Hybrid vigour, also known as heterosis, is the difference between the performance of the progeny and the average performance of the parents. In general, the more distantly the parental breeds are related, the greater the amount of heterosis that can be expected.

The main benefits result from:

• higher performance than expected for a range of traits through hybrid vigour
• combining the benefits of breeds is called 'breed complementarity'.

The main benefit of hybrid vigour occurs for traits with low heritability such as reproduction and adaptability traits. 

Table 1 illustrates the relationship between heritability and hybrid vigour regarding different categories of beef cattle traits. Reproduction and maternal traits have low heritability and response to selection will generally be slower compared to high heritability traits. At the same time, significant improvement in these traits can be made through programs that maximise hybrid vigour.

Table 1: Heritability and hybrid vigour comparison.

Quantifying the benefit of hybrid vigour

 A comprehensive crossbreeding trial undertaken by United States Department of Agriculture at the Meat Animal Research Centre highlighted the benefits achieved through a structured crossbreeding program for weaning weight per cow joined. This trial included crosses of Hereford, Angus and Shorthorn.

Compared to the purebred calves, the F₁ crossbred calves showed an 8.5% increase in weaning weight per cow mated on average. This was a direct function of hybrid vigour. While significant, a larger increase of 23.3% in calf weaning weight per cow joined was observed in the F₂ calves compared to the purebred. These calves were bred from first cross cows and obtained the additional 'boost' from maternal hybrid vigour (Figure 7).

Figure 1. Responses in weaning weight per cow mated from different crosses (Adapted from information in Gregory, KE and Cundiff, LV (1980)) 

Crossbreeding design and hybrid vigour

 The amount of hybrid vigour achieved will depend on the type of crossbreeding or composite system implemented. A composite breeding program is a crossbreeding system that is stabilised (inter-mating the crossbreds). Table 2 lists the types of crossbreeding systems, the levels hybrid vigour (both individual and maternal) retained and estimates of increases in weaning weight per cow mated.

Table 2: Crossbreeding systems and estimated levels of hybrid vigour

Selection and crossbreeding

 Crossbreeding should not be seen as an excuse for using ‘low’ performing genetics (ie bulls). Regardless of hybrid vigour, the performance of the crossbred herd will depend largely on the performance of the parent, the management level and the environment that is used.

Tool 4.02 can assist you in deciding whether crossbreeding appropriate for your enterprise.

References

• Southern Beef Technology Services Tools of the Trade - Cross Breeding fact sheet 
• NSW DPI Primefact 624 
• Gregory, KE and Cundiff, LV (1980) Crossbreeding in beef cattle: Evaluation of systems. J. Anim. Sci. 51,1224-1242.