4 - Modify trait emphasis in line with individual requirements
The process of developing a breeding objective is an essential and very sound genetic improvement principle. Even taking the easiest and most practical approach of using an index developed by a breed society (and therefore the objective developed during the development of that index) will be a sound first step in designing a breeding program. However, in all breeding programs there will be individual requirements brought about by differences in the production environment, markets and personal preferences.
A few examples that may require modification of trait emphasis are:
- the desire to minimise calving difficulty because of inability to handle calving difficulties or the unwillingness to do so (due to extensive enterprise or difficult topography for example)
- the desire to breed towards a polled herd
- the desire to improve cattle temperament
- the need to meet market specifications of higher yield or different maturity types
- personal estimations of future market requirements (bulls selected today won’t produce sale progeny for at least 18 months and in most cases 2-3 years).
Requirements such as these can easily be catered for within the bulls that are high ranking on an index. Bulls may achieve high index values for different reasons so applying an independent cut-off on individual traits will only marginally reduce progress towards a profit objective. As an example, the bulls represented in Table 4 would allow selection of high indexing but quite varying birth weight.
Table 4: Five young Angus bulls with similar index value but showing variation in other traits.
|Bull A||Bull B||Bull C||Bull D||Bull E||Bull F||Breed average|
|Calving Ease Dir (%)||2.4||-3.6||2.7||0.3||-2.6||2.5||0|
|Calving Ease Dtrs (%)||1.7||0.8||0.8||1||0.6||0.9||0.4|
|Gestation Length (days)||-5||-0.5||-3.5||-1.4||-2.8||-3.2||-2.6|
|Birth Wt. (kg)||1.9||6.3||3.6||3.2||7.3||1.7||4.5|
|200 Day Wt. (kg)||40||45||42||40||52||34||37|
|400 Day Wt. (kg)||86||79||90||80||94||88||69|
|600 Day Wt. (kg)||112||104||107||101||115||105||88|
|Mat. Cow Wt. (kg)||85||73||71||73||91||76||81|
|Scrotal Size (cm)||1.2||0.4||1.8||1.7||1.2||2.3||1.3|
|Days to Calving (days)||-4.3||-1.8||-3.2||-3.4||-2.8||-4.2||-2.6|
|Eye Muscle Area (cm2)||9.4||12.9||9.6||11.4||11.2||9.9||3|
|Rump Fat (mm)||1.2||0.8||0.5||2.2||0.3||0.4||-0.1|
|Retail Beef Yield (%)||0.4||1.6||0.6||0.7||1.3||1||0.2|
|Long Fed CAAB Index||159||158||158||158||157||157||90|
There are also traits that are important to the breeding enterprise for which there are no EBVs and therefore aren’t included in the index. An example of these are the structural traits such as teats and udders. There is little option other than imposing independent culling on these traits.
Another decision point for control of the individual traits and for inbreeding is when allocating bulls to the mating groups.
When allocating bulls to mating groups, reduce the risk of inbreeding and dystocia and match traits if required by:
- mating bulls with the highest EBV for calving ease to heifers but remember that half of the genetics for calving ease comes from the maternal grand sire so reducing calving ease may take more than one generation. Even older cows shouldn’t be mated to extremely high birth weight bulls because if you keep heifers resulting from that mating, they will carry genes for high birthweight
- possibly mating bulls from a breed with a lower mature size to heifers (especially effective in a crossbreeding program where differences in mature size and hybrid vigour can cause increased birth weights and therefore increased calving difficulties)
- matching strengths and weaknesses of cow groups by allocating different sires. An example may be earlier maturing (low frame size) cows mated to later maturing bulls or vice versa if maturity type is important to your objective
- minimising inbreeding through preventing the mating of bulls with their daughters or with cows that have a common parent (half-brothers and half-sisters).
What to measure and when
- Calving ease EBV for bulls allocated to weaner heifers or birth weight EBVs when calving ease EBVs are not available.
- Male parentage of all cows in the herd. This may only be done in age groups if individual identification is not recorded.
- Monitor growth rates, turn-off age and turn-off fatness (see Module 7: Meeting market specifications).
- Monitor feedback from kill sheets and note any unwarranted trends that may need correction (see Module 7: Meeting market specifications).