A Further Evaluation of Cow Productivity Index

Written by: Matt Woolfolk, ASA Director of Performance Programs

Hopefully, by the time this issue reaches your inbox, you have seen the changes to our selection index offering implemented in Digital Beef. If it’s your prerogative, you’ve taken the time to study how the changes to the $Feedlot formula are reflected in your herd, as well as the addition of the Cow Productivity Index (CPI). As the new index on the page, there’s undoubtedly questions about how it works. This article will walk through some of that aiming to give you a better understanding of CPI.

Let’s start with the breeding objective that defines CPI and, thus, the traits that get included in the model. This index mirrors the production scenario in which Shorthorn genetics are going to be most often utilized in the commercial sector: to produce own replacement heifers and steers that are a payday for their producer as feeder calves. As seedstock producers, we have been told over and over that the commercial cattleman wants cattle that don’t cause them problems, most recently by panel members Brian McCulloh, Dale Stith, and Jim Akers at Summer Symposium. Either that mantra is truly so important that it must be repeated, or we aren’t doing a very good job of it, so they must keep telling us. The goal of CPI is to help identify those genetics that we might classify as less apt to cause problems: calve on their own, raise a good calf to the weaning pen, keep doing it year after year without getting bigger cows than a rancher might want.

With that in mind, the traits that fit this index according to the economic model are described below:

Calving Ease Direct (CED) – It’s no secret that the first key to having a profitable calf is getting it into this world safe and alive. The CED EPD is a prioritized part of CPI for that reason. We don’t want calving issues, and neither do our customers.

Weaning Weight (WW) – The end marketing point utilized in the building of CPI is selling calves by the pound as weaned feeders. Obviously, that makes weaning growth genetics a significant component of CPI.

Yearling Weight (YW) – The YW EPD is included in CPI as the indicator trait of mature cow size and is weighted negatively in the index. While a genetic tool for cow weight is in the works at IGS (our genetic evaluation service provider), it is not available for use in our evaluations yet. Genetic studies have shown the correlation between yearling weight and mature weight to range from 75 to 85%. Of note, our BMI formulation has been put together in this same way since its inception, with YW being a negatively weighted part of that index as an indicator for moderating mature cow size as well.

Milk – Cows need to be able to produce enough milk to raise a healthy calf. While our hardest EPD to track, MILK is an important EPD in maternal selection. Too little MILK can leave you disappointed in your cows’ production. We also know that too much MILK can be an issue if you do not have the environmental resources to support heavier milking cows. The MILK EPD is included in a positive weighting in CPI.

Calving Ease Maternal (CEM) – If the goal is producing daughters that can go to work as productive cows, then they need to be able to have their first calf with no troubles. With that in mind, CEM is a part of CPI, albeit the least emphasized of the incorporated traits.

Stayability (STAY) – Longevity is a key to profitability for a cow. The longer she produces, the better chance she becomes a moneymaker for you. STAY is our genetic measure of the likelihood of staying in production longer, meaning a higher STAY EPD is predicting a higher chance of hanging around the herd. The STAY EPD is a significant component to CPI’s formulation.

Several times, I have been asked about why specific traits were not included in CPI or weren’t weighted differently. I reference a chat I had with Dr. Troy Rowan as he performed a third-party analysis of CPI where we talked about a “desired gains” index: putting things into an index to make the outcome what we want it to be, without it necessarily fitting the economic models geneticists use to build the index. Instead, Dr. Rowan advocates for selecting for specific EPDs that might not fit into the index alongside of index selection to make genetic progress. If you want to improve marbling or ribeye or any trait with an EPD while still looking at CPI, you can certainly do that by studying that data in conjunction with the CPI index.

A presentation from Dr. Matt Spangler of University of Nebraska during this summer’s BIF Symposium analyzed this topic well, and I encourage you to look it up on www.beefimprovement.org if you are one of those folks who is lucky enough to have free time. His topic was discussing the challenges of selection indexes for producers who don’t market cattle on a carcass quality grid (many indexes utilize this as an endpoint in the index models). In his presentation, Spangler laid out two scenarios and created indexes for them, with the objective in both of keeping replacement females: a “sell steers at weaning index” with EPD selection thresholds for carcass traits (EPDs not included in the index), and a “sell steers on the grid” index with no extra selection pressure for carcass (carcass EPDs were included in index).

The results of his trial were that the index that marketed cattle on the grid pointed him in the right direction for maternally oriented cattle but referred to it as “sub-optimal”. His test was better able to identify them via his sell at weaning index with selection pressures on carcass traits to. With my curiosity now peaked, I applied some of his tactics to our test population of sires for CPI. The chart to the right shows the average CPI for the top 50 bulls that also meet an EPD selection threshold. So, the top left value in the chart would be the average CPI of the top 50 CPI bulls in our test group that also are average or better for their MARB EPD. The top right box makes a stricter selection, cutting the MARB candidates to the top 25%. The same process is carried out for the other 3 EPDs on the table.

As expected, the more intense we make our selection criteria, we potentially sacrifice genetic merit as valued by the index. However, if we are willing to give up a little to apply that selection pressure on other traits, bulls that excel for CPI, carcass, and/or growth are out there to use.

There’s a lot to unpack any time that a new selection tool is introduced, and CPI is no different. Educating yourself on the available tools will always be important. Knowledge is power, and with knowledge of the tools that best suit your operation, your power to breed and improve Shorthorn cattle increases.