Incidence of scours has not changed in more than 20 years, despite wide adoption of scours vaccines. According to the National Animal Health Monitoring System (NAHMS), scours was reported in 1991 as the most common illness among dairy heifer calves and the leading cause of death (52.2% of deaths). In 2014, 23 years later, NAHMS reported that diarrhea was still the most common disease in pre-weaned heifers, affecting 21% of all heifers and causing more than half of all deaths (56.4%).
For decades, farmers have turned to a modified-live oral calf scours vaccination program to help protect calves against bovine rotavirus and coronavirus. To understand how colostrum can interact with these newborn oral scour vaccines, researchers at RTI (Research, Technology, Innovation) LLC., recently analyzed colostrum samples in vitro and determined the overall effect that the vaccine has in the presence of colostrum. Results show that the oral scour vaccine is inactivated and rendered ineffective in the presence of colostrum.
Study DesignThe study used colostrum samples collected from four geographical regions, including New York and Pennsylvania, Texas, Indiana and Ohio, and California. Each region provided eight colostrum samples: four from individual cows vaccinated with a dam-level scour vaccine and four from cows not vaccinated with a dam-level scour vaccine. The experiments were conducted using an in vitro cell-based assay. There were two designs utilized to replicate on-farm use of the oral scour calf-level vaccine. In the first design, researchers mimicked the on-farm delivery of colostrum and the vaccine together. In the second design, researchers waited 30 minutes after giving the vaccine to add colostrum, mimicking an on-farm colostrum delay.
When the colostrum was immediately added to virus samples from the modified-live vaccine, the vaccine was 100% neutralized by the colostrum antibodies in every sample, regardless of whether or not the host cow was previously vaccinated with a dam-level vaccine.
When researchers withheld the colostrum for 30 minutes, there was no statistical difference in the delay versus the non-delayed test. The majority of the vaccine was still neutralized. Breaking the delay down further, while colostrum from both vaccinated and non-vaccinated cows was proven to neutralize the vaccine, the colostrum from vaccinated dams neutralized statistically more of the vaccine than colostrum from non-vaccinated dams:
Table 1. Calf-Guard Neutralization
During a recent immunology symposium, Dr. Chris Chase, Department of Veterinary and Biomedical Sciences at South Dakota State University, reinforced the issues with maternal interference, which is when colostral antibodies from the dam interfere with the vaccine. To better explain the interference, he reviewed an illustration of neutralization within the intestine (see Figure 1 below).
“On the left, when colostrum is absent, the oral vaccine can bind to the host cell receptors, which triggers an immune response,” said Chase. “The vaccine antigen can stick on, enter in and then do what it needs to do.
“But when colostrum is present (right side), antibodies bind to the antigen, blocking adhesion to the host cell receptor and preventing an immune response,” added Chase. “If there are pre-existing antibodies already present, the antibody doesn’t care whether it’s a vaccine virus or if it’s a field virus. It’s going to neutralize it and prevent it from entering into the body.”
Instead of an oral calf scour vaccine, Chase highlighted the use of passive polyclonal antibodies to enhance immunity for newborn calves. According to the SDSU professor, these antibodies protect against both bacterial and viral scours. With vaccines, there are too many outside factors, making a 100% immunization response rate biologically impossible. But with an antibody product, Chase said farmers know exactly what they’re getting – a known and proven level of protection against scours.
Source: Bovinevetonline