Total merit indexes like NTM (Nordic Total Merit), JPI, TPI NM$ index, PLI, BPI among others are important genetic selection tools. The indexes differ by the traits covered and by the weight allocated to the specific traits.
Let’s look at the traits included in JPI and NTM and compare the weights of different traits for Jersey.
NTM places 53% of the total weight on health and reproduction traits, while JPI puts only 27%. NTM has some traits that are not covered by JPI being: Hoof health (2%), General health (6%), Calving direct (2%), Youngstock survival, calf survival in the early and late rearing periods (4%).
Daughter fertility has similar weights in JPI and NTM, both being at 11% weight while Udder health and Calving maternal have higher weight in NTM. It is important to note that Udder health index in NTM is based on the registrations of clinical mastitis – direct selection, while JPI has SCS as an indirect selection tool. JPI has higher weight on longevity, as JPI does not have most of the health traits that are included in NTM, so Longevity is used as indirect selection tool for better health in JPI.
As for production, JPI has higher weight on Production 53%, while NTM has lower weight on Production traits - 35%