Calculating indexes

To calculate a genetic index (often known as a proof), information is drawn from a variety of sources to produce the best possible estimate of an animal’s genetic worth. This includes information on the animal’s own performance, where appropriate, and on that of other family members.

An animal’s performance is a combination of genetics and environment, so allowances are made for age, lactation number, stage of lactation, herd performance and season. The most important component of a bull’s proof is his daughters’ performance. For a cow, the most important component, initially, is her own performance. If a bull or cow is too young to have any daughter or performance information of its own, its genetic index is usually calculated from its own genotype (or gene set), measured from codes along each strand of its DNA.

Traditionally, an estimated genetic index for young animals has been called a pedigree index (or parent average), as information was based on the animal’s family or pedigree. However, these terms are used less since the advent of genomic indexes.

In all young animal indexes, their family and genomic information become progressively less important as the animal accumulates its own performance information (or from its progeny).

Information included in genetic indexes comes from:

• Milk records organisations – production and cell count information
• Breed societies – type and locomotion information
• A combination of the two – fertility and longevity

Calculating genetic indexes for production or production-related traits usually takes information from five lactations. Calculating genetic indexes for type or type-related traits typically relies on details of heifer classifications.