Rotavirus can create a missed opportunity for sow farmers
Anthony Holowka, DVM with Four Star Veterinary Service in Lancaster, Pennsylvania, recently spoke to The Pig Site’s Sarah Mikesell to explain the clinical signs of rotavirus, how to treat rotavirus with natural planned exposure and a few lessons learned using natural planned exposure in the breeding herd.
What is rotavirus?
Rotavirus is viral enteritis, so it causes scours by blunting the villi tips which are the finger like projections that help the small intestine absorb feedstuffs. By blunting the villi tips, it leads to malabsorptive diarrhea in young pigs, and they don’t receive the nutrition they require. However, Dr. Holowka says most piglets do recover from rotavirus.
“Rotavirus typically causes scours in the farrowing house, and it can set pigs up for failure in the nursery. It’s important to keep it on your radar as it usually causes scours 3 to 5 days post-farrowing. Scours are sometimes seen and treated as a bacterial pathogen. If piglets don’t improve with normal antimicrobial treatment, it’s important to look into viral pathogens and environmental stressors,” said Dr. Holowka.
Rotavirus can stick with piglets in the farrowing house and slow them down, but Dr. Holowka said he doesn’t really see rotavirus being a primary issue downstream in the nursery.
Rotavirus treatment options
Vaccination is the mainstay, and it can be in a bottle or using feces or piglet intestines, which is generally called “feedback” and is a common method used on sow farms. Traditional vaccination is commercially available, but only for certain serotypes which can be limiting. There are three serotypes that are clinically relevant with rotavirus: A, B and C.
“We test for all three serotypes via PCR fairly routinely, and farms can be positive for A or B or C, a combination of two or all three. It sometimes seems that they eventually get all three serotypes, and it varies in sampling timepoints as to which serotypes your veterinarian finds,” he said. “The vaccine covers only certain serotypes, so some reach towards autogenous vaccines which can cover all serotypes. However, most vaccines companies specializing in this field have a minimum dosage requirement which can be limiting in smaller farms. The cost of vaccines can also be difficult for some smaller farms, so it’s nice to have another option.”
Natural Planned Exposure
Natural planned exposure is similar to the idea of manure feedback that sow farmers are familiar with. The idea is the same – exposing the breeding herd to a very high concentrated dose of rotavirus that’s actively circulating on the farm.
“We know it’s rotavirus, not anything else, because we’re testing before we administer it,” said Dr. Holowka. “Natural planned exposure is an on-farm live virus inoculation to your sows and gilts during gestation using our piglets to replicate the virus. The process is actually quite easy.”
Step #1 Diagnostic testing. Get tissue samples specifically from the small intestine, which is where the rotavirus causes damage. Send it to the lab, and they will determine if it is serotype A, B, C, or any variety of the three. The lab will also give you a Ct value, and hopefully, it’s a nice low value which equals a high viral load. In addition, culture the sample to ensure there’s no bacterial infections associated with it or other viruses. Thus, we want to make sure that the isolate is strictly rotavirus. This becomes our sample rotavirus.
Step #2 Infect the piglets. Take your material with most infective rotavirus found on sampling and feed to “colostrum-deprived” piglets. When the piglets are born, they cannot receive colostrum from the sow, so that when they receive the virus, they have no immune system from mom. The “no colostrum” rule is critical to the process. This will allow the naïve pig to rapidly replicate this virus without any immune system. Within 24 hours, these pigs have rotavirus and will be scouring.
Step#3. Create the inoculum. At 24 hours, the intestines of six to eight piglets are harvested (number of piglets is dependent on size of the farm), which will contain super high virus material. A small sample is sent to the lab to make sure it’s only rotavirus, and no other pathogens are present. Then, mix the virus material with soy milk. Antibiotic is added just in case there is any sort of bacteria, and you have your product. The veterinarian typically creates the batch of inoculant, and the staff feeds the material to the herd.
Step #4 Two-dose whole breeding herd treatment. The product gets mixed in water and then gets mixed in with feed. Depending on housing type, it can be fed directly to sows in crates or in feed troughs in open housing. Every animal needs to get a good dose – but they love it and will gobble it up. A booster is administered two to four weeks later.
Once the gilts and sows consume it, they are infected and it’s in their system. They don’t show signs and symptoms like piglets because their immune systems are more developed.
“Even if a sow or gilt gets just a mouthful that’s still millions of virus particles, so it’s very potent,” he explained. “It’s not as critical if we miss a sow, but the most important animals to ensure get a dose are the gilts. Rotavirus issues typically stem from the gilt population because they have a more naive immune system.”
Dr. Holowka noted that natural planned exposure does not provide piglets with an in utero immunity. It offers colostral immunity.
“Colostrum intake of the piglets is the key to transferring the immunity from the mother to the babies,” he said.
Lessons learned with rotavirus
Monitor. It’s important to repeat test after a planned time frame, especially if you start seeing more scours occur. Piglets might still pick up a mild amount of rotavirus, but it should be minimal. If you do see scouring, take tissue samples to make sure this is a rotavirus issue. There’s a chance it could be a bacterial issue or something else. Sapovirus is a virus that often causes confusion because it looks similar to rotavirus, it acts similar, and the timing is similar. Sapovirus might be a little later, like seven to 10 days of age when pigs are affected versus three to five days with rotavirus.
Storage. A large batch is made on farm aliquoted into 45mL tubes to be dispensed per protocol. These tubes are frozen in the on-farm freezer. These tubes can be frozen for long periods of time. Dr. Holowka has had success with storing up to one year, although storage factors are important to consider. Preferably, the type of storage unit is a non-defrosting (manual) freezer. However, most farms will likely have a household freezer (frost-free freezer). Frost-free freezers automatically prevent ice buildup and are therefore more inconsistent for storing sensitive material. There is also no current testing available to show the current viability of your stock. Therefore, to ensure proper viable material, re-sampling is critical to understand the on-going infection status of the herd.
