5-Culling policies

Implement sound culling, management and marketing policies to complement the genetic improvement program

For some traits, it may be more cost-effective to make improvement by culling non-performers or by management. Repeatability can be as important as heritability for traits that are repeated annually, such as calving success and weaning weight of the calf. Fertility traits tend to have lower heritability but are economically important in most breeding programs. In some enterprises, it is more efficient to improve fertility by culling non-performers, or by improving nutrition or management.

Management influences – especially nutrition – can overcome some genetic deficiencies. For example, lower fattening ability is not a problem if nutrition is adequate, such as in feedlot finishing.

One of the most important nutritional considerations is the time of calving. In principle, timing for mating should coincide with timing for reliable high quality feed (see Module 3: Pasture utilisation).

The chosen market should also be considered as a variable in the enterprise mix. Strategic decisions about which market to target should be made based on sound economic considerations. Chasing a high priced market may be a false economy if major changes to the breeding program are required.

For example, herds with high calving rates (greater than 85%) and a breeding program of selecting heifers by short joining (6 weeks) at a young age (15 months) will select for heifers with early age at puberty. If empty cows are culled after pregnancy testing for the second calf, the remaining cows in the herd will have short post-partum anoestrus. Both early age at puberty and short post-partum anoestrus are associated with improved lifetime reproductive performance. A culling procedure based on these principles will make only a small genetic improvement but it will improve the repeatability of these traits. Selecting for repeatability of a trait (ie selecting young animals for traits that will be repeated at older ages) is likely to improve profit more than just selecting for sires with higher fertility EBVs (ie days to calving, scrotal size).

Calving ease may be used as a second example. Again, heritability is low and the trait is very complex. A single-pronged approach will be unlikely to result in large changes, but multiple approaches including genetics, culling and nutrition can be very rewarding.

Maximum returns will result from integrating genetic improvement programs, culling and management.

What to measure and when

  • Performance level of economically important traits
    • calving rate
    • calves born in first cycle
    • compliance to market specifications (weight, fat, marbling)
  • Nutrition and climatic conditions
    • decisions to change should not be made in extremes, such as droughts or extremely good seasons
  • Age and weight at sale.

Commonly used genetics terms

Estimated breeding value (EBV) – an estimate of an animal’s genetic worth for a particular trait. The estimation can be based on the animal's own phenotypes or its' relatives, for the same or different traits to the trait of interest. This is made possible by knowing the genetic relationships between animals and the genetic correlations between the heritabilities of traits. The bull and cow each contribute a random sample of their genes to their offspring, half from each, meaning that half of the EBV of each parent is the contribution to their progeny.

Breeding objective – relates the goal of the breeding program to the traits that need to be improved to contribute to the overall enterprise objective (presumably economic gain, for the most part).

Selection index – a single EBV that describes how well animals suit a particular purpose (objective). It is a weighted combination of all available EBVs into a single dollar index value ($EBV).

BreedObject™ – a software package that can calculate a dollar index ($Index) value for animals specific to the breeding objective for your herd.