Changing calving dates
By Kris Ringwall
NDSU Extension Service Beef Specialist
When discussing major changes in the beef cow operation, calving date and cow size quickly come to life. The easiest to change is calving date.
Caution and considerable thought need to be used because, once changed, an early calving date is not easy to get back. Through the years of looking at calving intervals, most herds can come close to averaging a 365-day calving interval. Seldom do herds come in under 365 days. The majority come within two to three days in excess of 365 days.
Older cows usually leave the herd due to age or structural issues before they work their way out of a herd due to late calving. An example would be a cow with an average calving interval of 368 days. If she produces nine calves, her 10th calf would be projected to be born 30 days later than her first calf nine years ago. This means that changing the calving date is a big deal, and to err when one changes the calving date is even a bigger deal.
Many producers are looking seriously to change their calving date. The common indicator is a gradual delay in turning the bulls out and then gauging how the delay affected the herd. Changing the calving date shifts the entire cow nutritional plan and how nutritional needs are met.
The important, but sometimes missed, point is that the nutritional plan will shift in time but not change the requirements. The daily nutrient requirements of a cow are based on cow production and size, not time of year.
There are adjustments due to weather, but nutritional requirements remain. The land mass or production unit does not change significantly from one year to the next unless a major change in management has occurred. The production of grass can be tracked historically.
Lee Manske, range scientist at the Dickinson Research Extension Center, says nutritional values for grass from early May to the end of the grazing season in October have a very defined pattern. If one was to use crude protein as an indicator of value, the percentage of crude protein starts high. It usually is more than 17 percent in May and slowly decreases during the grazing season to less than 5 percent by midfall.
So, how do we match the calving time of the cow with the natural value of the grass? If one looks at the typical crude protein requirement of cows following calving, the value is 8-plus percent (depending on the size of the cow) for lower production expectations to 11 to 12-plus percent for greater calf production expectations. These values can increase by almost 1 percent by the time peak milk production kicks in during the second month of lactation, and then the values decrease to a low of around 6 percent at weaning.
There are two schools of thought. Producers have the natural or Mother Nature's way of producing protein that starts high in May and bottoms out in October. This is location-dependent. Every producer needs to get access to the numbers for his or her own location and environment.
The second thought is the nutritional requirements of the cow. These requirements are not dependent on location, but they are on cow type and expected production.
If one overlays these two thoughts, the natural tendency is to match or align the two concepts. Peak nutritional requirements should meet peak grassland production opportunities.
Peak lactation requirements are one month after calving, so it makes sense to have those cows that have month-old calves on a high-protein pasture in May. The pastures will decrease in protein production, depending on the grazing system, but that decrease will coincide with the gradual decline in protein requirements of the cow and calf.
It makes sense, then, that historical calving time in the northern Plains is March and April. The urge still is to change and move to a later calving date. However, the move is not because of nutritional needs but for labor reasons.