Extension Education: optimal Cow Size for Wyoming Cattle

Throughout the years, cattle producers have grappled with understanding the optimal cow size for maximizing productivity of their operations. 

Todåay, the average mature cow size in the U.S. is about 1,400 pounds, whereas the average mature cow weight in 1975 was about 1,045 pounds. 

Research has established, as cow weight increases, feed efficiency and reproductive efficiency decrease. Research has also shown as cow weight increases, dry matter intake also increases.

This article reviews some of the considerations cattle producers should keep in mind with increasing mature cow weights.

What has changed in the last 40 years?

A big factor is cattle producers today have had access to ever-improving genetic information. 

Over time, cattle have been selected heavily on growth traits such as weaning weight and yearling weight. Selecting sires with emphasis on expected progeny differences which improve growth characteristics can be effective ways to sell heavier calves at weaning. 

However, if heifer calves are also being retained as replacements, it could mean retention of growthier females into the cow herd. It’s then common for older and growthier heifers to be retained because those are the ones with a better chance of getting bred and rebred. 

If replacement heifers are retained in an operation, emphasis on maternal traits such as milk and maternal weight are not always a primary concern. 

Additionally, a large portion of cattle producers in the Intermountain West graze cattle on public lands and are charged on a per head or per animal unit month basis, rather than accounting for actual body size.  

A study at Utah State University compared economic differences of mature cow weights – 1,000; 1,200 and 1,400 pounds – grazed at various resource bases common in the Intermountain West. 

The results of the study showed when body weight was accounted for with grazing intensity, the smaller cows were the most efficient group and yielded the highest number of net returns across all resource bases. 

Further, larger numbers of small cows could be maintained compared to medium and large groups on the same resources. 

However, when grazing was managed on a per-head basis, as is common, the larger cow group generated the largest returns. These findings suggest grazing on a per-head basis may contribute to selection of larger cattle over time.

Cow size and pasture resources

For many operations, grazing plans and carrying capacities have been long established. However, mature cow weights are not always recorded, and weight increases can go unnoticed. This can lead to an operation which runs the same number of cows on the same pasture resources grandpa did. 

However, the needs of larger cows today aren’t the same as needs of smaller cows from the previous generations. Larger cows require more feed and more inputs. 

With increasing cow sizes over time, producers may need to consider efforts to improve grazing efficiency to support increased forage consumption, including additional feed and supplement inputs to maintain larger cows or reduce their carrying capacity to account for body weight changes and the pasture resources available. 

Tracking mature cow weights and establishing a baseline cow size would be a good first step in making sure pasture resources match grazing intensity. 

Preg check or vaccination times might be good opportunities to also record cow weights. If access to scales is a challenge, averaging pounds from sale receipts on cull cows can also be helpful. 

Cow size and reproductive efficiency

Larger cows have been known to have less longevity compared to smaller cows.

Oklahoma researchers found 1,400-pound mature cows have up to one less calf in their lifetime compared to 1,100-pound cows. 

Smaller cows have also been known to grow their calves more efficiently as their calves gain weight faster relative to dam weight compared to calves from large dams.

Additionally, larger cows require additional nutrients for maintenance and milk production. Therefore, if the environment is left unchanged and stocking rates are not adjusted accordingly, this could lead to overgrazing and/or thin cows and calves that don’t perform as well over time.

If retaining heifers, the use of moderate-sized sires with maternal traits may be a good tactic in mitigating increasing cow size. Purchasing replacement heifers with ideal maternal characteristics might also be a good strategy.

Summary 

Understanding how cow size affects production is an important part of the management puzzle. Balancing maternal and terminal traits is difficult but necessary, especially if cattle producers plan to retain their own replacement heifers. 

Cattle producers should consider maternal traits along with production traits when selecting breeding combinations in the future. 

If mature cow size increases over time, producers should be aware of it and account for changes within their management plans.   

Chance Marshall is a University of Wyoming Extension educator based in Fremont County. He can be reached at 307-332-2363 or cmarsha1@uwyo.edu.