To be profitable dairy producers need cows that calve easily, produce large quantities of high quality milk, and are healthy, fertile and long lived. USDA's index, Net Merit Dollars (NM$), is an economic index developed to breed exactly that kind of cow. NM$, last revised in 2010, currently puts 35% of the emphasis on production: 19% on PTA fat pounds. and 16% on PTA protein pounds. Health traits make up 48% of the index with productive life at 22%, somatic cell score at 10%, daughter pregnancy rate (DPR) at 11%, and calving ability (calving ease and stillbirths) at 5%. Udder composite is at 7%, and feed and leg composite at 4%. There is a negative weight of 6% on body size in the index because everything else being equal, smaller cows are more feed efficient.
Genetic progress by breed
The dairy industry continues to make genetic progress. Table 1 shows the genetic change comparing cows born in 2010 versus those born in 2005 for selected NM$ and individual traits. The table illustrates that the genetics of an average Holstein calf born in 2010 will return $324 more profit compared to 2005 genetics.
Holsteins have made relatively more genetic progress than the other breeds. The most probable reason for this is that Holsteins have had a huge advantage in numbers of young sires progeny tested during this time. Increased genetic progress because of genomics may increase Holsteins' advantage further in the future. Yearly progress for milk, fat and protein has been impressive and steady for the past 40 years. Progress in the health traits (SCS and DPR) from 2005 to 2010 has been a little slow. A reason for the slow progress for DPR is that national genetic evaluations for DPR were not available until 2003. It has taken a few years to even get high PTA DPR young sires into the progeny testing system. Also, breed association indexes, such as Holstein Association's TPI, put less emphasis on the health traits than found in NM$.
Holsteins increased by only 0.43 for DPR while Jerseys actually show a slight decrease of -0.08. This is not to say that Holsteins are more fertile than Jerseys. Holsteins started at a much lower level. The average Jersey born in 2010 has a genetic value of 29.2% for DPR while Holsteins are at only 25.2%. Holsteins need to make a lot more genetic progress for DPR before they begin to catch up to the fertility of Jerseys.
Even though there has been negative weight on body size in the index since 2000, the upward genetic trend for body size has been difficult to slow. Dairy producers who want bigger two-year-olds at first freshening should concentrate on improving heifer nutrition and management rather than selecting for high PTA stature.