Maternal Productivity Index

Scientists at Agriculture Canada’s Lethbridge Research Centre have developed a “maternal productivity index” or MPI, for Hereford bulls. The MPI combines the factors of fertility, productive herd life, maintenance costs and genetic potential for growth into a single measure.

Until now, bull buyers have had to consider a wide range of genetic factors when looking for a Hereford bull that will produce cows with good mothering ability. When the MPI is implemented, it will reduce the guesswork and will allow fairly straightforward decision-making. For example, a bull with an MPI of 125 is better than a bull with an MPI of 115. The 125 bull is going to produce heifers that are going to stay around longer, and be better-producing females.

Until now, most measurements of genetic traits have focused on production improvement in offspring, such as growth rates and carcass quality. The complex MPI calculation incorporates weaning weight, cow weight and “stayability.”

Weaning weight provides information on calf growth and a cow’s milk production. Cow weight is an indicator of the cow’s maintenance costs. Stayability measures the probability of a cow weaning at least three calves during her lifetime.

The MPI was developed as a flexible index that can incorporate other traits over time if deemed appropriate. But according to two pilot projects, it is working fine as is.

The MPI measurements will become a standard part of genetic evaluations conducted each fall before the bull buying season. But it will be only one of the many factors a buyer has to consider when purchasing a sire. The bull still has to have four legs, pass the semen test, be interested in females and have the desired structural features.

It would be interesting to see whether the MPI could be adapted and used for elk bulls. Ed.