Skip to Content

The Weekly News Source for Wyoming's Ranchers, Farmers and AgriBusiness Community

Reproductive wrecks

by Wyoming Livestock Roundup

In a cow/calf herd, multiple factors affect pregnancy rates, and many of those factors need to be considered to prevent potential challenges.

According to Cheryl Waldner, Western College of Veterinary Medicine (WCVM) professor in large animal clinical sciences, “The bottom line for cow/calf herds is to get cows cycling at the start of breeding season and increase conception rates to ensure herd fertility.”

During a Beef Cattle Research Council (BCRC) webinar titled, “Preventing reproductive wrecks,” on Jan. 23, Waldner discussed body condition, nutritional deficiencies, reproductive tract infections and bull performance as factors of cow performance.  

Body condition 

In terms of cow/calf herd nutrition, body condition is a major management tool for producers, noted Waldner. She explained the Canadian body condition score ranges from one to five, with one being thin cattle and five being fat cattle.

“Producers may ask,  How does body condition relate to the cows and pregnancy rates?’” she stated.

Looking at a 2002 study with individual animal data collected from 30,000 cattle, Waldner noted cows with a body condition score of two compared to those with a three were between 3.5 and 4.2 times more likely to be open.

“The facts make a pretty compelling case for the relationship between body condition and pregnancy rates,” Waldner mentioned.

She added body condition should be analyzed particularly right before calving and in the breeding season.

“When comparing a cow with a body score of less than three to a cow that’s at least a three, with no change in body score after calving, the thin cow’s chances of being open the next fall increase 1.5 times,” Waldner stated.

In short, there is strong evidence pregnancy rates are influenced by body condition, which is certainly something for producers to keep in mind for their cow/calf herds, according to Waldner.

Thinner cows are also more likely to abort calves, she noted, adding, “Cattle with a body score of less than 2.5 before calving are more likely to have difficult births, and cows with a body score less than three are more likely to have stillborn calves.”

Nutritional impacts

Waldner mentioned one nutrient significantly associated with pregnancy rates is copper.

In a 2007 community pasture study, blood samples were taken from cows before breeding season, and results showed two- and three-year-old cows with low copper levels had increased open rates, she noted.

“There is a significant association between copper and pregnancy rates,” added Waldner. “In 2014, blood samples from 2,000 cattle indicated 43 percent of those cows were copper deficient.”

Molybdenum, another trace mineral, is also a problem because it ties up copper to the point it can’t be utilized, she mentioned.

“Cattle pick up molybdenum primarily from feed and soil,” she added. “Other minerals to watch for that tie up copper are iron and sulfate.”

“When looking at the role of nutrition, body condition is the problem hiding under the surface, but nutrition, including minerals, impacts all parts of reproductive performance and should be monitored,” Waldner stated.


Reproductive issues mainly affect cows and heifers, but bulls are an easier place to check for and prevent potential problems.

“Along with breeding soundness evaluations, bulls should be tested for venereal diseases like trichomoniasis and vibriosis to avoid infecting cowherds,” Waldren stated.

She pointed out veterinarians usually take samples from bulls during breeding soundness evaluations and then send the samples to a lab or process them at their clinics.


“Do bulls actually test positive on the trichomoniasis and vibriosis tests?” asked Waldren. “Fortunately, the trichomoniasis test is 96 percent accurate.”

“Unfortunately, vibriosis is more difficult to deal with in testing,” she added, mentioning there’s a test that looks for bacterial vibriosis DNA using samples taken for trichomoniasis. 

“The test for vibriosis is about 85 percent accurate, but vibriosis is very sensitive to temperature, so cold weather decreases the chance of accurately detecting the disease,” she stated.

When producers try to decide whether to test for 

Back to top