The American Angus Association provides various selection tools to assist cattle producers in making informed breeding decisions. Two of these tools, the Maternal Weaned Calf Value ($M) and the Weaned Calf Value ($W), focus on the same stage of the production cycle — commercial cow-calf profitability. 

Both breeding objectives are defined as targeting a commercial cow herd replacing 20% of their females annually with heifers retained from their own supply. The remaining cull females and all male progeny are sold as feeder calves after weaning.

The introduction of $M represented a significant evolution in how the Association approached maternal indexes. In 2018, the Association, alongside Angus Genetics Inc. (AGI) and under direction of the Breed Improvement Committee, began revising and incorporating more traits into its indexes to provide the most robust profitability predictions possible. The result was $M, which offered a more comprehensive and economically relevant tool compared to the traditional $W.

Comparison between $M and $W

While the breeding objectives remain the same, $M includes a broader range of economically relevant traits, offering a more well-rounded assessment of profitability in a cow-calf operation. 

$W strictly focuses on four traits — birth weight, weaning weight, maternal milk and mature cow size — and $M replaces birth weight with calving ease. Additionally, $M includes traits for heifer pregnancy, foot conformation and docility, while still incorporating weaning weight, maternal milk and mature cow size. This broader range of traits leads to reranking individuals when comparing the two indexes. 

Profitability for both indexes is focused on the total pounds of weaned calf. Like any profit function, the revenue from these pounds is linked to the costs involved. These costs cover feed resources for maintaining and breeding females, replacing breeding-age females, and any other direct costs of the calf up until weaning age.

The biggest difference producers notice between the two $Values is the focus on cost reduction for the cow-calf operation. 

Figure 1 shows response to selection graphs for both $M and $W. For $W, there is a strong emphasis on increasing weaning weight, maternal milk and mature cow size. 

Though focusing solely on these traits will increase overall pounds of weaned calves, it doesn’t account for diminishing returns on maternal milk and only slightly addresses mature size related to feed costs.

In contrast, $M places greater emphasis on reducing the cost of the cow-calf operation, including feed resources. 

In a 10-year selection period, $M aims to reduce costs by limiting cow size, introducing diminishing returns on maternal milk and emphasizing other maternal traits while maintaining current weaning weight levels. Mature weight is crucial for cost savings in cow-calf operations because larger cows have higher maintenance energy needs. Cows with higher requirements need more calories just to maintain themselves.  

Top $M performers and MW EPDs

Figure 2 shows the top 200 registration sires all ranking in the top 25% for $M. The top 25% $M performers are compared against their mature weight (MW) expected progeny differences (EPDs).

While there is a relationship between $M and MW EPDs, the top 25% of $M performers have MW EPDs that vary widely — some are above average, some are below. For example, the second-highest $M bull in the top 200 has an above-average MW EPD.