The CDCB health traits will be added to the Lifetime Net Merit (NM$) formula starting in August. They will be combined into a health trait sub-index called HTH$, which will not be published separately.
You can find the relative value (%) for the traits in HTH$ in Table 1. DA, MAST, and METR represent over 80% of the index, due mainly to the higher costs and heritabilities associated with those traits.
The correlations between HTH$ and the other traits in the NM$ formula are in Table 2. HTH$ is moderately to highly correlated with the health traits that were already included in the formula (PL, DPR, SCS, HCR, CCR, and LIV). The heritability of HTH$ is low (0.01) as are many of the health traits.
A comparison of the 2017 and 2018 NM$ formulas is in Table 3 below. The addition of HTH$ to NM$ results in slightly less weight on some of the traits already in the formula. In addition to new health traits in the index, NM$ now puts slightly more emphasis on the yield traits. SCS emphasis decreases because indirect correlated health costs are now allocated directly to HTH$.
The Fat to Protein ratio shifts to favor fat more, as the price paid for Fat is increasing and the price paid for Protein is decreasing (see Table 4 below).
Emphasis on SCS decreases since MAST is now directly included through the HTH$ index. PL emphasis also decreases slightly because later lactations are less valuable now that replacement heifer prices are lower.
Table 5 shows the expected genetic progress per trait for the 2017 and 2018 NM$ formulas.
The new 2018 formula will result in more progress for Fat, Protein, and FLC, and less progress for PL, DPR, CA$, and HCR.
The correlation between the 2017 and 2018 NM$ indexes are very high. For current industry genomic Holstein bulls the correlation is 0.998, and for current active, proven Holstein bulls, the correlation is 0.999.
Of the current top 100 NM$ genomic bulls, 88 remain in the top 100 NM$ using the 2018 formula.
Of the current top 100 NM$ active, proven bulls, 95 remain in the top 100 with the new formula.
Ever-changing industry indexes serve as a reminder that your own farm’s customized genetic plan is as important as ever. When you set your emphasis on the production, health, and conformation traits that matter to your own bottom line – and stick to the plan you set – you’ll continue to maximize the progress you make in the direction of your own farm’s goals – even when other indexes change.
Holstein values are weights (expressed as percentages) from composite formula calculated by Holstein Association USA (2017) and, therefore, do not sum to 100.