Introdcution - Vaccinating Pregnant Cows
Last month I wrote a blog on science behind vaccination. A number of colleagues contacted me to find out my views on vaccinating pregnant cows. I am aware that many veterinarians still believe that pregnant cows should not be vaccinated for fear of causing abortion. That was what we were taught in veterinary schools. I therefore decided to spend some time researching on this topic, both on how and from where this rule of not vaccinating in pregnancy came from and secondly, is there a valid answer to this query based on scientific evidence.
What is true for human may not be so for cows
Vaccinate cows to protect calves too
An exactly an opposite viewpoint has emerged that vaccinating heavily pregnant cows might be of benefit to calf health. Let us examine this on the basis of science. In case of ruminants during first three days the cow secrete milk, called colostrum, which is rich in antibodies, growth factors, vital nutrients and immune cells. Interestingly on feeding colostrum to now-born calf, all these molecules are absorbed intact. This wonderful phenomenon happens only in first few days of calf-life and later on the gut is closed to intact absorption. Not much is known on metabolic pathways of synthesis of colostrum, how it is triggered and then whole lot of genes responsible for colostrum is turned off within 3 days and the udder starts producing normal milk of interest here is to understand the origin of antibodies and other molecules in colostrum.
My own studies prove that under trigger from certain calving process factor(s) there is mobilization of secretary antibodies (IgG1) from immune system to blood and then to udder. We found that this mobilization of antibodies against all possible infections the cow was exposed during its life starts at around 14-21 days to calving whereas maximum antibodies could be demonstrated in blood during last 3-5 days to calving. When consumes these antibodies are absorbed intact in new born calf and provide passive immunity and priming of immune system which has been shown to ensure protection against important infections as well as optimum growth. So, when a pregnant cow is vaccinated the memory cells, which on one hand will provide immunity to mother cow and in addition large amounts of antibodies will also be secreted in colostrum to provide passive immunity in early calf life. This was proved in a study done by me in a farm that was having high incidence of E. coli metritis and calf-scour. The farm was losing good cows to repeat breeding and superior genetic calves would succumb. We prepared vaccine from E. coli isolates and vaccinated, actually hyperimmunized, cows in advanced pregnancy. We found colostrum was rich in E. coli antibodies which provided protection to calves reducing morbidity and mortality and also helped cows as incidence of metritis came down significantly. This also led to further studies on hyperimmune health milk. In this study, pregnant cows during 7 and 8 months of gestation were hyperimmunized with H. pylori (common causal factor for gastric ulcers) antigens. Colostrum from such cows was found to be rich in H. pylori antibodies. When these cows were further vaccinated during lactation, milk was also found to be rich in H. pylori antibodies. These and other published studies prove the point that vaccination in pregnancy would be of benefit to even calves. For example, in areas, where FMD is endemic and there is associated calf mortality, vaccinating pregnant cows with FMD would confer passive immunity in young calves fed on colostrum from such hyperimmunized cows.
Are such vaccines available commercially?
In USA and Canada, and possibly other developed countries, entro-pathogen vaccines such as E. coli, Salmonella, Rota and Corona virus vaccines are available. In order to protect calf from these entero-pathogens, the cow should be vaccinated in later pregnancy leading to high antibody levels in colostrum and better passive immunization of the calf.
In conclusion, veterinarians should come out of the myth that in pregnancy cows should not be vaccinated as vaccination-associated abortion is a remote possibility. Abortion however could occur due to maternal factors and infections which is largely due to placental pathology. It will be pertinent to mention here that studies show that as far as killed vaccines are concerned, these are safe at any stage of pregnancy whereas, live modified vaccines should be handled carefully in pregnancy. Studies have shown that in case of live modified vaccines, first vaccine dose must be given before breeding and in that case subsequent vaccination in advanced pregnancy would be safe and highly beneficial to cow as well as calf.