Producers should let the condition of their cattle and forage dictate when to wean calves, two North Dakota State University Extension Service specialists say.

“Cow herd management is oftentimes a great art of matching a cow’s changing requirements to an ever-changing forage resource base,” says beef cattle specialist Carl Dahlen. “A recurring theme through the years is the variability in moisture accumulation and the coincident variability in forage growth. In cases of limited forage availability and declining forage quality, cow body condition and calf growth can be impacted.”

But only 17 percent of producers use forage availability and the physical condition of cows as the most important factors in determining when to wean.

“For the health of pastures and the long-term productivity of breeding females, producers should consider the condition of forages and the cattle when making decisions about when to wean,” Dahlen says.

The 2013 growing season was unusual for pasture production and quality across North Dakota. Much of the western region received above-average moisture throughout the summer, while the central and eastern portions received excessive moisture early, then limited rain in July and August. These moisture patterns create two different scenarios that result in differing forage quality issues, according to rangeland management specialist Kevin Sedivec.

On average, forage production on North Dakota’s rangeland was at or above normal throughout much of the state. Eighty percent of the state’s forage grows from late May through early July. Most of the state received sufficient moisture in May and June to grow grass.

“However, if you were the unfortunate livestock producer who did not receive much rain in July and August, you will have quantity and quality issues,” Sedivec says.

The May and June moisture created ample standing growth. However, as the moisture became deficient, green regrowth was limited, and what is left is mature growth that is low in quality. These producers also will lack the 20 percent growth that occurs from late August through late September (regrowth that occurs with late-summer moisture and cooler weather).

In the end, cattle grazing low-quality, mature plant material that lacks regrowth will suffer from protein, vitamin and mineral deficiency, the specialists say. In addition, overgrazing pastures in the fall may reduce pasture yields during the next growing season.

“For those ranchers who received moisture throughout the summer, quantity and quality will be adequate until a killing freeze,” Sedivec says. “Once we receive a killing freeze, quantity still will be fine, but quality will deteriorate within two weeks following the event.”

In a mature cow, body condition score and plane of nutrition just prior to breeding often are highlighted as having a major impact on reproductive success, Dahlen says. However, management around the time of weaning also can be a major driver of a reproductive event that can occur more than six months in the future.

Producing milk for a calf requires a lot of energy, and once weaning occurs, a mature cow’s nutrient requirements are the lowest they will be all year. A majority of fetal growth occurs during the third trimester of gestation and, thus, cow nutrient requirements begin to increase during late gestation.

“If heavy lactation or poor pasture growth has cows in low body condition, weaning calves prior to the third trimester of pregnancy may allow cows to put on body condition without supplemental feeding,” Dahlen says.

As cows get further along in gestation, thin cows will need to consume more calories to gain weight prior to calving. The additional calories required to gain condition later in gestation translate to greater expense for producers to get cows into proper condition at the time of calving.

“Calving in good body condition is very important because most cows lose additional body condition after calving,” Dalen says. “Gaining body condition after calving is difficult because of additional energy demands of milk production and repairing the body from the trauma of calving. Cows that are thin at calving may never reach the point where they have sufficient body condition to become pregnant during the next breeding season.”

Characteristics of pastures being grazed and the condition of cattle grazing pastures can be major drivers of overall herd productivity, Sedivec says. If either is in a declining state, producers should take proactive steps to alleviate strain on the system and salvage future productivity.

NDSU Agriculture Communication - Sept. 18, 2013