Managing herds to prevent reproductive diseases decreases abortion, death loss
Most often, reproductive diseases are identified by ranchers during pregnancy checks when the veterinarian comes to the ranch and finds more open cows than normal. For producers who don’t pregnancy check, reproductive diseases may be identified when not as many calves show up as expected. Finally, abortions lead ranchers to start thinking about reproductive diseases.
“When we have an abortion, unfortunately, we only diagnosis the actual cause of the abortion between 30 and 44 percent of time,” says Kansas State University Veterinarian Gregg Hanzlicek. “Diagnostics are very, very difficult in abortion work-ups.”
However, Hanzlicek says that contagious bacteria and viruses are often implicated as the reason for abortion, and producers should be cognizant of the potential negative impact of these diseases on their herds.
One cause of viral abortion is IBR, or infectious bovine rhinotracheitis
“Since 2014, we have seen a huge increase in the number of IBR abortions,” Hanzlicek comments. “This is a respiratory and reproductive organism that is transmitted through aerosols.”
He notes respiratory droplets are enough to transmit IBR, and urine or vaginal fluids can also pass the disease to other animals.
“IBR is a herpes virus,” he adds. “There are a lot of positive animals out there that do not show signs.”
Hanzlicek compared IBR to shingles in humans, where humans occasionally show clinical signs of shingles, but often, the virus is latent within the system.
“We’ve seen a huge increase in IBR abortions,” he comments. “One of the beliefs was that the use of modified live vaccines in pregnant cows was to blame. We’ve looked at several aborted calves and found the same strain of IBR that was in the vaccine.”
Hanzlicek strongly emphasizes this does not mean producers should not use modified live vaccines.
Rather, he says, “Follow label instructions, and make sure to consult with a veterinarian on vaccination protocols.”
Another disease of concern is bovine viral diarrhea virus (BVD).
“This is like IBR,” says Hanzlicek. “It’s both a respiratory and a reproductive organism.”
Also similar to IBR, transmission of BVD occurs through aerosols and fluids, including saliva, vaginal secretions, uterine secretions and semen, all of which can carry the virus.
“We talk a lot of persistently infected (PI) and transiently infected (TI) animals,” he continues. “The thing we have to prevent in our cow/calf herd are persistently infected calves. Those are the calves that are born with BVD. They have a huge amount of virus in all their systems.”
Hanzlicek continues, “Any animal they are exposed to is also exposed to huge doses of this BVD virus.”
TI animals are not born with the disease, but they are infected for a short period of time. TI livestock can also transmit the disease, but their viral load is much less than PI animals.
“It’s important that we try to prevent both TI and PI animals from getting into the cow/calf operation,” he explains.
If a fetus is exposed to BVD from two months to term, there is the possibility the calf will be aborted.
“Most often we talk about exposure at 40 to 100 days. If the fetus is exposed during that time and it survives, then there’s the opportunity the calf will be born a PI,” Hanzlicek comments.
Additionally, BVD has an impact on fertility and early embryonic death.
“I looked for studies where there was natural exposure to BVD on this topic,” he says. “In one study, they took a group of cows that had not been exposed to BVD previously and exposed them to a PI cow and a PI calf during breeding.”
The cattle that were exposed and developed an immune response during the breeding season has a pregnancy rate of 44.4 percent. The cows that were exposed but did not mount an immune response until after the breeding season has a pregnancy rate of only 22.2 percent.
“Fertility or embryonic death had a huge impact on these herds,” he comments.
Another study using heifers that had never been exposed to BVD were exposed to PI and not-PI animals.
“Those heifers that were exposed to a PI calf four days after insemination had a pregnancy rate of 44 percent,” he says. “The group that was not exposed to a PI animal had a pregnancy rate of 79 percent.”
Additionally, tests showed that the exposed group lost an additional 11 percent of fetuses from 20 days to 77 days. The group that was not exposed did not lose any fetuses.
“BVD does have an effect on fertility and early embryonic death,” Hanzlicek comments. “We still have PI animals in our cow/calf herds, even though we do a good job vaccinating and with bio-security.”
Neospora caninum is a protozoa that has increased in prevalence in the Midwest and West.
“We can have both horizontal and vertical transmission of this disease,” says Hanzlicek. “Horizontal is transmission from animal to animal, and vertical transmission comes from dam to calf.”
He adds that Neospora has several outcomes for infected fetuses.
“Infected fetuses are carriers for life, meaning the fetus has the opportunity to pass Neospora on to calves later in life,” he says, adding that abortion is also a potential outcome.
Canines are definitive hosts of Neospora. The organism reproduces in canines, including coyotes and dogs. Neospora exists in the feces, which can contaminate water or feed. Then, if goats, sheep, horses or cattle ingest the organism through infected feed or water, they are subsequently infected.
“One of the risk factors for positive herds are the number of dogs that are there, since dogs can carry the bug,” Hanzlicek says. “The number of birds in the area is also a risk factor.”
“I’m not sure we know much about this disease,” he adds.
Effect on the herd
Research has shown that livestock positive for Neospora caninum are two to three times more likely to abort their calves than dams not exposed.
However, abortion risk decreases by the length of the infection.
“There’s a lot of research that shows that in herds that are not newly infected, as the cow or heifer becomes older, even though she remains positive for the infection, her opportunity for aborting decreases through time,” he says.
Newly infected herds often show epidemic abortion, with a large number of animals aborting about the same time.
“For herds that have been positive for some time, Neospora typically presents as a nagging decrease in fertility or a higher abortion rate than normal,” Hanzlicek says. “It often waxes and wanes.”
He adds, “As we think about this disease more often, I’m hoping more people start to study it.”
Hanzlicek also emphasizes significantly more research should be done to better understand Neospora and its impact.
Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org.