Ask cow-calf operators why they calve when they do and you'll get a wide array of answers. Everything from, “I want a big calf at weaning” to “I don't want to nursemaid cows when the corn needs to be planted.”

Occasionally, someone may respond with, “This time of year fits my grass the best.” I'm not saying this is the right answer, but it may come the closest to roping in the biggest economic factor in cow-calf production — managing feed costs.

In much of the U.S., winter-feed costs are the most expensive element in the cow business. The 60 days post-calving are when cows have their highest nutritional demand, both in quantity and quality. Those two factors make a good case for why time of calving is critical to economic success.

For a cow with low to average milking ability, energy requirement increases 30% to 50% at peak lactation compared to maintenance. As we've bred more milking ability into our cows, nutrient requirements for lactation have likewise increased.

A modern, high milk-producing cow may have nearly double the energy requirement she had at maintenance. That translates to double the feed costs at peak lactation, which is why matching calving time and peak forage availability is so important.

On most farms and ranches, pasture or range is the cheapest source of energy and protein to put in a cow. Meeting as much of the peak nutritional need associated with lactation through grazing is usually a good first step toward profitability.

Matching Calving And Grass Cycles

So what does it really mean to match calving and grass cycles? First off, nowhere in the U.S. is forage supply constant all 12 months of the year. Even an area with a mild climate has peaks and valleys in forage supply. Conversely, there are areas that have good grass for only a few months each year.

Often, the cost of keeping pastures growing in less favorable times can be quite expensive. Since the peaks and valleys are generally fairly predictable, timing calving to capitalize on the forage peaks is our goal.

The most important economic trait of a beef cow is reproductive efficiency. Thus, the real target of our grass management is to get cows bred back.

To maintain a 12-month calving cycle, a cow needs to rebreed about 90 days after she calves. We know that cows need to be gaining in condition to be fertile and breed back quickly, so the real issue for calving season is how consistently can we breed a cow cost-effectively in that time frame?

The two main factors affecting cow condition are availability of appropriate quality pasture and environmental conditions. That means the optimum calving season will vary by geographic location. Let's look at some examples and discuss the pros and cons of different calving seasons.

I'm going to start close to home and look at endophyte-infected tall fescue in the hot, humid, lower Midwestern-upper South environment. Traditional calving time has been February-March, probably due to competition with crop farming later in the spring and the organization of feeder calf sales for October-November.

Late-winter calving puts breeding in May-June when tall fescue is most toxic and temperatures are steadily rising. The result is a lot of open cows — unless they're supplemented or very well-adapted genetically. Frequently, the hay being fed to these cows was baled off those same toxic fescue fields and is too low in quality to meet the lactation energy demand. As a result, cows are already losing condition coming out of winter.

Contrast that with fall calving in an infected-fescue environment. September-October calving occurs in fall when fescue regrowth is the highest quality of the year and when very few of the highly toxic stems and seed heads are likely. Breeding occurs in December-January when stockpiled fescue can be of adequate quality to support both lactation and cow body condition.

In addition, temperatures are conducive to getting cows settled in a timely manner. In a recent study, we found the cost of wintering fall calving cows on stockpiled tall fescue to be one- fourth that of wintering matching pairs on hay and creep feed. Plus, the stockpiled pasture provided superior cow and calf gain and similar conception rates.

That's a pretty good case for fall calving being a better alternative. Throw in the better marketing options for a spring-weaned calf compared to a fall-weaned calf, and fall calving looks even better.

A Look At A Western Range Scenario

Let's look at a western range scenario with a good grass season of only a few months from May to August and a long winter on either dry range or expensive hay. If our goal is to have cows in good condition and gaining weight for breeding, calving to the first blades of green grass in late spring may be a good approach. Calving a little later in late spring or early summer, allowing cows to gain weight on the range flush, can also work as long as grass supply lasts through breeding season.

The worst scenario in this environment would be fall calving with seven months of hard winter and poor-quality feed.

What about regions like the Gulf States where winter annuals make up an important part of the forage supply?

With Bermuda grass as a ready supply of summer pasture and heat-tolerant cattle, calving in late winter on the tail end of winter annuals, then going to Bermuda for the summer, may not be a bad deal. Backgrounding the weaned calves on fresh winter annual forage and roughing cows on stockpiled Bermuda can make a pretty cost-effective pasture program.

Regardless of location, the same basic principles govern fundamental profitability in the cow business. Maximizing the use of low-cost pasture and range to ensure that cows get bred in a timely fashion is still the first key to success.

This principle underscores the importance of knowing the production and quality profiles of the different forage resources on your farm or ranch. If you have a handle on that resource, it's much easier to make sound decisions about the best time to calve in your environment.

Jim Gerrish is a research assistant professor with the University of Missouri Forage Systems Research Center in Linneus.