One of the most common questions asked by seedstock breeders is “what size herd do you need to obtain effective results from TACE?”
There is no minimum herd size requirement for herds wishing to participate in the TransTasman Angus Cattle Evaluation (TACE), however the nature of the TACE analysis means that there are a number of
additional considerations that small herds need to make to ensure they obtain effective results from TACE.
In particular, small herds need to pay careful attention to two main concepts, being contemporary group formation and the creation of genetic linkage.
Although the TACE analysis is underpinned by a very sophisticated analytical model, the basic mechanism by which it works is to directly compare the performance of an animal with the performance of other “similar” animals within the same contemporary group.
Put simply a contemporary group can be described as animals from the same herd, of a similar age and run under the same conditions i.e. animals that have had the same opportunity to perform.
For most performance traits, calves will be analysed in the same contemporary group if they:
Were bred in the same herd Are of the same sex Are of the same birth number (i.e. twins are not compared to single calves)
Small herds must try and ensure there are at least two animals that meet the above criteria if their performance records are to be analysed effectively by TACE. When there is only one animal represented in a contemporary group, there are no other “similar” animals to which its performance can be directly compared and thus the performance submitted for the animal will not be used in the TACE analysis, rendering it ineffective.
As illustrated in Figure 1, the effectiveness of an individual animal’s performance record increases as more animals are represented within each contemporary group. The general aim for all small herds should be to maximise contemporary group size as much as possible.
Genetic linkage gives the TACE analysis the ability to compare the performance of animals from different contemporary groups. This is particularly important for animals running under different conditions in different herds, but also relates to the comparison of animals running in different contemporary groups within a herd. For example, animals born in the same herd but born in different years.
For TACE to compare animals from different contemporary groups, be it in the same herd or in different herds, each contemporary group must have some performance recorded progeny from common animals (typically common sires) so that the performance recorded animals in each group are genetically linked.
As a simple example of genetic linkage, consider the scenario outlined in Figures 2 and 3 where 3 different mobs of calves are compared.
There are environmental differences between the groups – Contemporary Group 1 (CG1) has relatively poor nutrition, Contemporary Group 3 (CG3) is average and Contemporary Group 2 (CG2) is relatively good. All of the progeny in each group are by different sires (Kevin, Tony and Harold), with a common link sire (Malcolm) existing in each contemporary group.
While it is not possible to directly compare the performance of the calves in the different groups due to the environmental differences, the link sire makes it possible to compare the progeny of the different sires represented in each group by acting as a benchmark in each group.
When compared to the link sire Malcolm, Harold in contemporary group 3 can be considered to have the highest genetic value for 400 day weight performance, followed by Kevin in group 1, followed by Tony in group 2. Graphically, these differences are shown in Figure 3.
For the purpose of this exercise, all sires are assumed to be joined to cows of equal genetic merit, although in practice, TACE accounts for any genetic differences that exist between the dams.
Management Strategies for Small Herds
Taking into consideration the concepts of contemporary group formation and genetic linkage, it becomes obvious that small herds, if not managed with these concepts in mind, may struggle to maximise the effectiveness of their performance recording.
Because of their low animal numbers, small herds tend to have high numbers of single animal contemporary groups and may struggle to create genetic linkage, thereby reducing the effectiveness of their performance recording.
There are however a variety of management strategies small herds can implement to increase the effectiveness of their performance recording.