Genetic improvement is a key factor in managing a profitable dairy herd. The majority of the genetic improvement in dairy herds is achieved through genetically superior replacement heifers. Consequently, selection criteria for service sires should be updated routinely.
Net Merit (NM$) is a tool that can be used on dairy farms when making sire selection decisions. NM$, which is computed by USDA Animal Improvement Programs Laboratory, estimates lifetime profit based on incomes and expenses relevant for today's dairy producers. Traits included in NM$ are: fat (lb), protein (lb), productive life (mo), somatic cell score, udder composite, feet/leg composite, body size composite, daughter pregnancy rate, and calving ability($). (Learn more about NM$ in my previous post.) Genetic evaluations are updated three times each year in April, August and December.
The relative economic weights for fat and protein used to compute NM$ closely reflect the multiple component pricing that applies to Michigan dairy producers. The emphasis on the health and fitness traits is based on the relative value of reducing those particular problems in a herd.
The genetic merit of bulls marketed through artificial insemination (AI) organizations continues to improve with each release of updated genetic evaluations. Consequently, sire selection goals set by dairy producers a year ago may be outdated today.
The following table lists the NM$ values for various percentile ranking levels for each breed. Knowing where service sires rank relative to other active AI bulls is helpful in determining if the sires meet the herd goals. To maximize genetic improvement, it is recommended that the service sires in your herd average at or above the 80th percentile.
NM$ levels of top percentiles for AI sires by breed. April 2011 USDA Sire Summary
(Number of bulls in the current active AI population for each breed are in parentheses.)
Herds using DHI services can obtain the average NM$ and percentile ranking of service sires from the DHI-202 Herd Summary or the PCDART on-farm computer system. To ensure that a herd's replacement heifers will be genetically superior, sire selection criteria should be reviewed and updated periodically. It is important to communicate these goals with semen sales representatives also.
Net Merit $ can be used as a key selection tool to identify high ranking service sires. Use the percentile ranking information to determine where your current group of service sires rank.
Source: Kathy Lee, Michigan State University Extension