Beef Cattle Longevity Traits
3.4.1 General
Longevity is an essential part of any breeding goal, reflecting the ability of an animal to cope successfully with the environmental conditions that arise in the production system. The length of the life of an animal can be calculated from its life history data as any survival trait may be defined as the length of time between two events. Longevity may be measured, from birth or from onset of production to the date of measurement of the specific trait for the last time in an animal’s life.
Life history data which are essential for longevity traits (see elsewhere in these guidelines) are birth date, calving dates and date of disposal. In addition for the calculation of longevity traits the cause of disposal needs to be recorded.
3.4.2 Calculated longevity traits
The trait generally suggested to describe the longevity of an animal is the productive life span (or also sometimes referred to as productive herd life). Length of productive life is the period of time between the start of production and the end of productive life. As detailed in these guidelines, this trait may be calculated if the recommendations for recording life history data are followed. The endpoints for the calculation of the length of productive life need to be defined. Typically the productive life of a cow starts at her first calving and ends with her death. In using this data in a genetic evaluation, however, two problems have to be taken into account.
Firstly, incomplete records have to be considered in calculating the length of productive life where a different endpoint than the death of an animal is available. Examples are longevity data of animals which are still alive or which were sold for commercial use. To exclude incomplete records from the evaluation or consider them as dead would lead to biased results. One way to deal with this problem is to use indirect longevity indicators such as whether a cow is still alive at a certain age (‘Stayability’). This method is however associated with a great loss of information. Therefore, it is suggested, that incomplete data are treated as censored and special statistical tools are designed for coping with such data used in analysis. For the latter case, the correct code for cause of disposal is mandatory.
Secondly, for genetic evaluation the ‘functional longevity’ should be the trait of interest, i.e. longevity corrected for performance. In this context, culling for low productivity is disregarded since performance is used as a different selection criterion. Only culling for health problems or other non-production causes is taken into account. As for dairy cattle, the performance being corrected for may be milk yield assessed by weaning weight or a weight at a fixed age.
In many cases, early predictors of productive herd life is used for breeding value predictions in young animals. These predictors are usually associated with linear type traits, body measurements and production records.
