5 - Implement sound culling, management and marketing policies that complement the genetic improvement programs
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 be lowly heritable but 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 may not be a problem if you are producing store or feeder animals, which will receive adequate nutrition to fatten at other supply chain stages.
One of the most important nutritional considerations is the time just prior to mating (conception) and calving. It is important that breeding cows are on a rising plane of nutrition at conception so that they are able to support the developing foetus. Cows also have their greatest nutritional demand during lactation, which usually coincides with the time of conception, if you aim for your cows to have a calf every year. Therefore in principle, the period of calving and mating should coincide with the time of the year of reliable high quality feed (see Module 2: Managing your feedbase).
The chosen market should also be considered as a variable in the enterprise mix. Strategic decisions on 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.
As a case study example; herds that already have high calving rates (greater than 85%), a program of selecting heifers by short joining (6 weeks) at a young age (15 months) will select for heifers with early age at puberty. Then if culling empty cows on pregnancy testing for the second calf, the cows that remain in the herd will be those that are 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 only make small genetic improvement but will improve the herd productivity for these traits. Selecting for repeatability of a trait (i.e. selecting young animals for traits that will be repeated at older ages) is important when also selecting sires with higher fertility EBVs (shorter, more negative days to calving and higher more positive scrotal size).
Calving ease may be used as a second case study; heritability is again low and the trait is very complex. A single pronged approach will be unlikely to result in large changes while a multi-pronged approach 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 such as:
- calving rate
- calves born in first cycle
- compliance to market specifications (weight, fat, marbling specification)
- 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
Breeding objective: the goal of the breeding program and the traits that need to be improved to contribute to the overall enterprise objective, which is presumed to be primarily economic gain.
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 $EBV.
BreedObject™: a software package that can calculate a ‘dollar index’ value for animals specific to the breeding objective for a herd.
Estimated breeding value (EBV): the estimate of an animal’s breeding value or ‘genetic worth’ for a particular trait. The estimation can be based on (phenotypes of) the animal itself and/or its relatives, for the same and/or different traits to the trait of interest. This is made possible by knowing the genetic relationships between animals and the genetic correlations between and 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.