by Sally Colby
In a shining example of optimism meeting reality, Dr. Rob Swackhammer explained what shouldn’t have happened in a group of young heifers. A new farmer acquired 10 cows from his grandfather and rented out the other half of the barn to help pay the bills. The pregnant heifers from the grandfather’s herd arrived in September. A group of feedlot cattle that would be housed in the rented portion of the barn arrived in November. The animals were housed separately and handled as two separate herds with different people caring for them.
“Problems started a month after the feedlot cattle arrived,” said Swackhammer. “The first pregnant heifer got sick with a very high fever and nasal discharge. Even though she recovered from the illness, she aborted a fetus that was judged to be approximately four months of age.” Sampling of the fetus revealed a diagnosis of IBR (infectious bovine rhinotracheitis).
The issues continued into January, when three pregnant heifers became ill. While they didn’t seem quite as sick as the others, they aborted. Samples showed those heifers were infected with BVD (bovine viral diarrhea).
“In February, what should have been done a while ago finally got done,” said Swackhammer. “The heifers were vaccinated with a killed vaccine for IBR, BVD, PI3, BRSV and lepto.” Heifers received a booster in March, but another heifer aborted. Two calves were born, lived for two weeks but were weak and eventually died.
Three calves were born in April, and all seemed healthy. In May, one of those calves became ill and died despite extensive treatment. A post-mortem exam indicated death was due to mucosal disease from BVD infection. In June, blood samples from the two remaining calves revealed persistent BVD infection. Since there were no other pregnant animals at the time, those two were kept with the heifers and eventually sent to slaughter.
What went wrong? “The optimistic view is that the cattle brought in from the grandfather’s farm were healthy,” said Swackhammer. “In reality, it should have been obvious that these heifers had very naïve immune systems and came from a herd that had never been vaccinated, and were susceptible to any disease they were exposed to.”
While the owner of the heifers thought the extra income from renting part of the barn would pay some of the bills, the reality was that the newly arrived feedlot calves were from a mixed source, were stressed, brought active IBR and BVD infections to the farm and infected heifers across the shared eight-foot gate.
Swackhammer explained why the incoming heifers weren’t vaccinated: “It was just too hard to do,” he said. “At the time, the only way to catch the animals was to lasso them and tie them to a beam that we hoped wouldn’t pull the barn down. It was incredibly labor intensive.”
Swackhammer added that when a small herd isn’t the primary source of income, amenities such as handling equipment tend to be a low priority.
The issue was solved, but not without time and effort – beginning with shipping infected calves before the bull was introduced. “We decided to take a break on rebreeding any of the heifers,” said Swackhammer. “They were vaccinated with a modified live vaccine and boosted in a couple weeks. In reality, there was probably some natural immunity, but it should have been done first.”
Admitting that he was the owner of the heifers, Swackhammer said the lesson was key to both his veterinary practice and his farming career. The key take home message for him was that a farm or barn should be set up to make it easy to do the right thing.
“Managing by hope isn’t good enough,” he said. “Set it up so animals are easy to catch – that’s what I drill home to producers even if they only have five or six cows. Buy one less cow and spend money on a chute.”
Inadequate biosecurity was another issue that Swackhammer said should have been obvious. “There should be no contact,” he said, “and ideally no shared air space for at least three weeks between resident and new animals. That allows the new animals to shed any viruses they may have picked up.” He added that “new animals” includes any owned animals that spent time off the farm and later return.
The third lesson was economic – an inadequate immunization program resulted in no calves and no income for one year. “This is something I drill home to small beef producers,” said Swackhammer. “Not being the primary source of income, optimism often outweighs reality.”
Swackhammer said for herds with a tight calving window, an open cow modified live vaccination program is best way to prevent losses. The second best option is annual vaccination with a killed vaccine followed by an appropriate booster, but that may not be enough to prevent PI (persistently infected) calves or abortion. Such a program should prevent clinical BVD in cows but isn’t likely to protect unborn calves.
“Prevent entry of the BVD virus,” said Swackhammer. “Make sure you have a solid vaccination program for both animals already on the farm as well as purchased animals. Test potential new animals for BVD before allowing them on the farm and have a three-week quarantine for new and returning animals.”
Swackhammer explained that BVD exposure to pregnant cattle occurs across the placental barrier and infects the fetus. The outcome depends on when the infection occurs. If it occurs close to fertilization, the consequence is reduced conception rates. If the infection occurs when the fetus is less than four months, the results can be embryonic death, abortion, retarded growth or PI. If the pregnant female is infected at four to six months gestation, the results can be congenital malformation of the eye and central nervous system, fetal mummification, premature birth, stillborn or weak newborn calves. There’s a chance some calves will be born normal but test positive.
“The biggest issue with BVD is the PI animals that shed large amounts of the virus which continues the problem for years because they infect other animals,” said Swackhammer. “PI calves may appear normal but die young.”
Swackhammer recommended maintaining a closed herd if possible, including the bull. Vaccinate animals with BVD and test for PIs two weeks prior to moving animals. “When you’re purchasing animals, when possible, move animals with your own truck directly from the farm to another,” he said. “Isolate all new arrivals for two weeks in a well-ventilated area away from the rest of the herd.”