Animal Health & Welfare

The majority of traits differ in the extent to which genetics, as opposed to the environment, influence the measurement observed (i.e. they differ in heritability). Whilst most traits have a heritability of around 0.30 (i.e. 30% of the differences observed are due to differences in genetics), the value for calving ease is fairly low (0.12).

Because 88% of the variation between animals in calving ease is due to environmental influences such as management, feeding and season of calving, it makes it even more difficult to obtain accurate genetic evaluations for it. This can only be done effectively using BLUP (best linear unbiased prediction).  Edinburgh Genetic Evaluation Services at SAC will soon be using BLUP to calculate estimated breeding values (EBVs) for calving ease for several of the major beef breeds.

When using BLUP to calculate the calving ease EBVs, information from a number of different sources are considered to help effectively separate the effects of the environment and genetics to ensure fair comparisons can be made between animals. These sources include: the animal's own performance records for calving ease, its contemporaries in the same herd, those of relatives across different herds and also the animal and relative's genetic merit for other recorded traits (e.g. birth weight, 200 day weight, 400 day weight, gestation length, muscle score and muscle depth).

Because its heritability is low, the accuracy of an EBV for calving ease is also low if only the measurements on the animal itself are considered. However, much better accuracy can be obtained by also considering the information provided by all of these other sources. Whilst the value of information on relatives is quite obvious, it is also important to recognise that most of the other traits recorded have some degree of genetic relationship (correlation) with calving ease. As a result, records collected on them also provide an important source of information for calculating the calving ease EBVs.

[For a more thorough overview of BLUP, we recommend Simm(1998) 'Genetic Improvement of Cattle and Sheep' - as cited in the reference list]