Source: Lactanet
by: Hannah Sweett, Ph. D. and Brian Van Doormaal
To improve producer understanding of the Lifetime Performance Index (LPI), Lactanet has removed the mathematical formula nature of our annual communications, replacing it with visual aids (see below). For each breed, proof correlations with LPI are published as an important measure of its relationship to each trait and the LPI subindexes. Based on the genetic gain for LPI achieved in recent years within each breed, the trait correlations with LPI have been translated into estimates of genetic response over the next five years that can be expected on a trait-by-trait basis when producers apply average selection intensity for LPI to achieve their breeding objectives. Higher intensity on LPI selection would result in a greater genetic response.
Key Points to Remember:
- The relative weight of each subindex in LPI, and the relative emphasis of each trait directly included in each subindex, are presented in the “%” column in the chart for each breed below.
- Just because a specific trait is not directly included in a subindex, doesn’t mean you won’t make genetic progress for the trait when selecting for LPI. The correlation between a trait and LPI (column title of “LPI Corr”), provides an excellent indication of how much genetic gain you can achieve.
- Genetic correlations range from -1.00 to +1.00 with values near zero meaning no practical genetic response should be expected.
- In the “5-Yr” column, the LPI correlation value for each trait is converted into the expected genetic progress in the typical herd over the next five years expressed in proof units (Production traits in kilograms, type traits in Estimated Breed Values (EBV), and all other traits in Relative Breeding Values (RBV)).
An Example
For the Production Index (PI) in the Holstein breed, a 60:40 ratio on Fat Yield versus Protein Yield results in a correlation with LPI of 0.81 and 0.74, respectively. In other words, every 1 standard deviation gain from selection for LPI will result in a correlated response of a 0.81 standard deviation gain for Fat Yield and 0.74 for Protein Yield. In addition to these traits, a correlation with LPI also exists for Milk Yield, Fat Deviation, Protein Deviation, and Lactation Persistency despite them not being directly included in the PI subindex. This 60:40 ratio on Fat Yield and Protein Yield translates to an expected 5-year genetic gain of 534 kg for Milk, 42 kg for Fat and 28 kg for Protein in the average Canadian Holstein herd. As another example, selection for LPI in the Holstein breed is expected to give 3.4 RBV points genetic gain for Herd Life over the next five years as well as progress of roughly three EBV points for each of Conformation, Mammary System and Feet & Legs.
Click here for a PDF of the chart below.
