"To maintain a 365-day calving interval, rebreeding has to occur by 82 days after calving," said Warren Rusche, SDSU Extension Cow/Calf Field Specialist. "Cows need to recover from calving and start cycling again during that time period while providing enough milk for their growing calves."
These extensive demands after calving impose significantly higher nutrient requirements on cows, Rusche explained.
"Depending on her potential for milk production, a cow could require as much as 40 to 50 percent more energy and protein compared to the last two months of gestation," he said. "Her needs for nutrients such as vitamin A, calcium and phosphorus are much greater as well."
A major obstacle cattle producers' face in meeting cows' needs during early lactation is the biological priority for nutrients.
"The first priority for any animal is to meet first their maintenance needs. The next priority in the case of 2- and 3-year old cows would be their requirements for growth," Rusche said.
Providing milk for her calf, Rusche said is the third priority.
"Finally, if her nutrient intake is high enough she'll breed. All four priorities need to be satisfied or there will be no calf to sell next year," he said.
Another factor to keep in mind is weather conditions.
"Now that spring is here, cold stress due to the absolute air temperature becomes less of a concern. However, spring moisture can create its own challenges," Rusche said.
He explained that a hair coat that is completely soaked loses all its insulation value. Under those conditions, the energy requirements increase by an additional 2 percent for every degree that the wind chill temperatures drop below 59 degrees Fahrenheit.
"Furthermore, as little as 2 inches of mud can increase the maintenance requirements of beef cattle by 10 percent," he said.
So how can ranchers meet the needs of cows in the most cost-effective manner? The answer, Rusche said, depends somewhat on when calving season begins.
"If the start of calving season is timed so that peak grass production coincides with early lactation, forage resources might very well be sufficient to meet her needs without relying very heavily on harvested feedstuffs," he said.
Those feed savings are one of the greatest advantages of delaying calving to match up with grass production in a given environment.
Rusche said that if a ranch management system involves calving earlier in the year, then the nutritional plan needs to take into account the cow's higher requirements during early lactation.
"Ideally, the feedstuffs have been tested so that the highest quality forages are saved for this timeframe and the proper supplements are provided if needed," he said.
Another challenge producers need to keep in mind, is the way nutrients are partitioned by the cow's organism which makes it difficult to feed her enough after calving to increase body condition.
"The typical response by the cow when more energy is fed is to first increase milk production before adding body reserves," he said.
Rusche said this is a big reason the standard recommendation is to feed cows or heifers to attain a body condition score of 5 or 6 by calving time.