Quick Calculation of Lifetime Net Merit

Superceded by 2003 update

Net merit as a measure of lifetime profit (AIPL NM$1 (11-00)) includes many supporting formulas that are not really necessary to calculate Net Merit (NM$). A quicker and easier way is described below.

The following formula and example can be used to verify calculations. A NM$ of +311 with 77% REL resulted for an example Holstein animal with the PTA and REL listed in the table below.

311 = (0.018*1000) + (2.14*40) + (4.76*30) + (28*1.0) + (-154*(3.00-3.10)) + (-14*-1.0) + (29*0.5) + (15*-0.5)

Note that the breed average SCS (3.10) must be subtracted from PTAscs. A Fluid Merit (FM$) of +312 and Cheese Merit (CM$) of +314 resulted from similar calculations except that economic values for FM$ and CM$ were substituted.

Net Merit measures lifetime profit. The range of values is about 3 times as large as for the profit per lactation reported prior to August 2000. Base changes for the individual traits included in NM$ totalled $61, so a theoretical conversion between the new August 2000 NM$ formula and the previous NM$ formula used until May 2000 is provided by

new NM$ = 3 times (previous NM$ - 61)

Reliability of Net Merit is computed officially from the reliabilities of all traits using a quadratic function, but can be approximated very simply. Because numbers of daughters for most traits are similar except for productive life (PL), reliability of NM$ can be approximated from the reliability of yield times .8 plus the reliability of PL times .2. An approximate reliability of 76% for NM$ is calculated as

76% = (80%).8 + (60%).2

Average first-lactation SCS for cows born in 1995 were: