Breeding
Changes to PLI
By Marco Winters
Aug 15, 2007 - 6:32:09 AM

Profitable Lifetime Index (£PLI ) - Guernsey breed

PLI – the National breeding index enables selection for improved net margin per cow lifetime and has been updated in August 2007. The Profitable Lifetime Index for coloured breeds has just under 50% weight on production and just over 50% weight on ‘fitness’ traits.

Predicted genetic response to selection on the new PLI indicates that alongside increased production, Lifespan will increase, SCC will decrease, Feet and Legs and Udder traits will improve.

Traditionally we also talk about the relative weight of various traits in the PLI index. Although it has to be pointed out that this doesn’t necessarily reflect the effect of selection on the index, it does give the user an idea of relative importance.

The chart below gives a representation of proportional weights of traits in PLI, and a breakdown of PIN. A general comment to the reported weights is that although 11.4% of the new PLI index is on direct selection for type traits, it has a considerably higher impact through the indirect contribution it has on Lifespan. For example, the Lifespan PTA of a typical first crop proof is nearly 60% based on type data, because at that time no actual survival data exists and type is used as a predictor (together with Family information and SCC).

Calculation of £PLI

For bulls with Locomotion proof available - (i.e. most bulls with UK daughters)

= ( -0.027 * Milk + 0.8 * Fat + 1.71 * Protein + 25.4 * LS + -0.19 * SCC + 1.10 * Locomotion + 2.79 * Udder) * 3.3

For bulls with only a Foot and leg proof and no Locomotion proof - (i.e. most imported sires)

= ( -0.027 * Milk + 0.8 * Fat + 1.71 * Protein + 25.4 * LS + -0.19 * SCC + 1.76 * F&L + 2.79 * Udder) * 3.3

Use of £PLI

The primary use of £PLI is to simplify selection for economic merit. It is produced for all breeds separately and should be used as an initial screen to identify which bulls to use within breeds and to select cows within the herd from which replacements should be bred. Once this initial selection of top PLI animals is made other genetic factors of importance can be considered.

For a list of top bulls available in the breed please follow click here.