Pregnancy rates are the most important economic trait in cattle operations
In a Nov. 23, 2020 North Dakota State University (NDSU) Extension newsletter, NDSU Extension Veterinarian and Livestock Stewardship Specialist Dr. Gerald Stokka notes if producers had to assess the success of their cow herd based on a single statistic every year, it should be pregnancy rates.
“Beef cow pregnancy rates are important numbers to track because reproduction is the most important economic trait in a beef cow herd,” he states.
Dr. Jason Sawyer and Dr. Rick Machen of the King Ranch Institute of Ranch Management (KRIRM) agree, noting reproductive rates are the foundation of reproductive function on cow/calf operations.
“Obviously, if cows do not become pregnant, then no calves are produced for revenue generation the following year. Revenue from culled cows is not a result of production. It is the liquidation of an asset which must be replaced – usually at a higher price – if production is to continue,” they explain in the Spring 2020 KRIRM Newsletter.
“Pregnant cows must successfully produce a live calf, and live calves must be weaned and sold before production revenue is generated. It is intuitive improvements in reproductive success, or the prevention of reproductive failure, drive cow/calf enterprise productivity,” they add.
Misguided solutions
In order to reduce the rate of open cows on an operation, Stokka points out many producers use misguided solutions which actually don’t address the fundamental reason for low pregnancy rates, such as changing vaccination protocols.
“Meaningful discussion to find solutions requires a systematic approach to practical management recommendations,” he says, noting it is important for producers to provide veterinarians with information related to production on their operation.
This includes calving dates, pregnancy checking information by fetal age, cow body condition scores (BCS), cow age, cow BCS by age, cow age by pasture information, bull age, cows exposed per bull and length of the breeding season.
Additionally, they should provide information on biosecurity of the herd related to purchases, exposure to the main herd and exposures to neighboring cattle.
Calving season analysis
In addition to working closely with veterinarians to improve reproductive rates on their operation, Stokka recommends producers follow a six-step analysis to investigate where the fundamental issue lies.
The first three steps look at issues related to calving season.
First, Stokka says producers need to evaluate what time of year they calve their cows.
He notes cows which calve during late winter into early spring require more nutritional energy to breed back for the next breeding season. Comparatively, cows which calve late in the spring or early in the summer may experience a decrease in forage quality in late July and August, which can impact fertility.
Next, Stokka encourages producers to look at their calving season distribution and determine when the majority of their calves are born.
“Is it the first 21 days, the first 45 days, the last 30 days or scattered throughout the calving season?” he asks. “This information provides some evidence of inadequate bull power, which may be related to dominant bulls, lame bulls, injured bulls or inadequate BCS and cow nutrition during the breeding season.”
Stokka notes a large number of cows determined to be pregnant late in the breeding season may be an indication of reproductive disease such a vibrio or trichomoniasis.
The third step on the list is to determine the number of calves born related to the number of cows determined to be bred during pregnancy checking. According to Stokka, this number helps producers indicate fetal loss due to abortions – noticed or unnoticed – and stillbirths.
This number may also serve as an indication of fetal infections including bovine viral diarrhea, infectious bovine rhinotracheitis, leptospirosis, neospora, fungal infections and other possible pathogens. Additionally, fetal losses can be due to high nitrates in forage resources, Stokka notes.
Parent age and BCS
Steps four and five in Stokka’s six-step analysis look at cow BCS and the age of both cows and bulls.
Stokka says the fourth step asks, “What is cow BCS, and what is cow BCS by age?”
“Younger cows – two and three years of age – and cows more than 12 years old will generally carry less condition than middle-aged cows,” he explains, further noting this has a direct relationship on their ability to rebreed and conceive the next season. “This is because young cows are still growing and lactating, and older cows will have more difficulty staying in condition because most of their incisor teeth will be missing.”
Next, he says producers should analyze the ages of their cows and bulls and how it relates to pasture assignments.
“Herds with younger or older cows in common pastures, regardless of bull numbers, will generally have a greater number of open cows,” he states.
While the number of cows exposed per bull is important, Stokka says bull age is even more important.
“Older and more dominant bulls tend to serve the majority of cows, so the number of bulls may not be as important as the age of all of the bulls in a pasture. Running two 14- to 16-month-old bulls with a single dominant, older bull technically counts as three bulls,” he explains.
However, in reality, Stokka notes this may only actually be the equivalent of running one and a half bulls because dominant bulls do the majority of the breeding.
He also mentions producers should invest in semen evaluations prior to breeding season, and in pastures with low pregnancy rates, bulls should be tested again after the breeding season.
Biosecurity and vaccination
The sixth and final question Stokka says producers should ask themselves is if they make biosecurity and vaccination protocols a priority.
“All purchased cattle and other herd additions should have a testing and vaccination history. If not, then implement quarantine procedures. Even with testing and vaccination, do not introduce new additions into the herd prior to the start of the calving season,” he concludes.
Hannah Bugas is the managing editor for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
