Source: Lactanet Canada
Written by: Hannah Sweett, Ph. D. and Brian Van Doormaal
Since its introduction in 1991, the Lifetime Performance Index (LPI) has been a crucial tool for dairy farmers and breeders, guiding informed selection and mating decisions. Over the years, the LPI formula has evolved alongside industry breeding objectives with the inclusion of additional traits. The latest update, in April 2025, marked the launch of a modernized LPI for seven dairy breeds, including Guernsey. Let’s delve into these recent changes so you can make the most of your breeding decisions.
Five Subindexes for Balanced Breeding
The new formula includes five subindexes for the Guernsey breed, namely Production (PI), Longevity & Type (LTI), Health & Welfare (HWI), Reproduction (RI), and Milkability (MI). Each of these subindexes are published on their own and combined into LPI while maintaining the previous LPI scale, providing several options when making selection and mating decisions. Figure 1 shows the relative weights of each subindex in the LPI formula for the Guernsey breed. The subindexes were developed in consultation with the breed associations, industry partners, and breeders by identifying the traits to be directly included as well as traits that are favorably correlated with the subindex, even if not directly included. Each subindex is defined in more detail below along with the traits included for the Guernsey breed.
Figure 1. Relative Weights of Subindexes in the Guernsey Modernized Lifetime Performance Index
The Production Index (PI) is similar to the previous Production component of the LPI with the aim of maximizing fat and protein yields thereby increasing profitability. This subindex is also positively correlated with Milk Yield, Fat Deviation, Protein Deviation and Lactation Persistency.
The Longevity & Type Index (LTI) aims to enhance herd longevity favouring functional conformation through selection for Herd Life, Mammary System, Feet & Legs and Dairy Strength.
The Health & Welfare Index (HWI) improves disease resistance with selection for Somatic Cell Score. In combination with superior management, the HWI will lead to healthier, more disease resistant cows thereby decreasing expenses.
The goal of the Reproduction Index (RI) is to achieve genetic gain for female fertility and calving performance, which is represented by Daughter Calving Ability. Selection for this subindex also yields progress for Calving Ability.
The Milkability Index (MI) is a new component of LPI with an aim to optimize milking efficiency designed to help all dairy farmers regardless of their production system. In addition to moderate weights on Milking Speed and Temperament, this subindex includes mammary traits related to desired udder and teat attributes.
Quickly Identify Animals that Standout for each Subindex
To help you compare subindex values and identify elite sires, each subindex is expressed on a standardized scale. The average proven sire is set to 500 with a standard deviation of 100, which means that two-thirds of proven sires will fall between 400 and 600. Favourable values will reach 700 or more. For each animal, the subindex values are published on the LactanetGen.ca website on their Genetic Evaluation Summary page along with the combined LPI value. This page includes histograms for each subindex that provide a quick reference to see the strengths and weaknesses for an animal.
Personalizing Your LPI
If you are looking for a more tailored approach geared toward your individual herd goals, you have the option to create your own personalized LPI (pLPI) by customizing the percentage relative emphasis on each subindex. In just three easy steps you can view your pLPI alongside the official LPI for each animal:
- Create an account on LactanetGen.ca
- In your “Preferences” page, select Guernsey as your preferred breed and then modify the subindex weights to create your pLPI.
- View your pLPI via either the Animal Query or Group Query results.
Summary
The LPI has been updated to reflect a more modern approach to balanced breeding, combining important traits into five subindexes for the Guernsey breed. You may wish to make selection decisions based on this official LPI, individual subindexes values and the histograms, or create a pLPI to prioritize subindexes that are most important to you. With LPI, you can boost genetic progress and select for a herd that is high performing, efficient, and long lasting!
