We must take into account the production periods where animals are naturally stressed (e.g., parturition and weaning) or production cycle phases where our management practices (e.g., commingling and transport stress) would predictably impair immune function. “We know there are genetic differences in the duration and magnitude of immune suppression in periparturient cows,” Kehrli says. “But practical ways to include immune performance in a selection index are only a distant thought even to those of us conducting research in this area.”
Relationship with antibiotics
Antibiotics have significantly lowered mortality rates of many bacterial diseases, suggesting that antibiotics fill a void where both innate and adaptive immunity are failing to optimally protect against mortality. “Furthermore, some classes of antibiotics are known to accumulate inside phagocytic cells of the innate immune system and in so doing help the phagocytic cell more efficiently kill an ingested bacteria,” Kehrli explains.
Antibiotics are certainly helpful as evidenced by the fact that antibiotic treatment can sometimes be life-saving for individuals with bacterial infections. However, the innate immune response is also critical for antibiotics to be useful, as evidenced by the fact that animals with defects in innate immune function, such as defects in neutrophil function, develop repeated bacterial infections that cannot be effectively controlled long-term with antibiotics. “So I would say that antibiotics and the innate immune system work hand-in-hand to fight off bacterial infection,” Woolums says.
Today there is abundant evidence that cross-talk between the innate and adaptive immune systems is vital to a successful vaccination program to prevent disease. “We already know quite a bit about the effects of various physiological stressors on neutrophil and lymphocyte functional activities, as well as the reduced ability of an immune-suppressed animal to respond to vaccination,” Kehrli notes.
“However, we don’t know all of the underlying causes of poor responses to vaccines and what contribution dysregulation of the innate immune system makes in these situations,” he adds. “Hence, it is critical that we invest in research to provide a better understanding of what components of the innate immune system are necessary for effective vaccine responses and how we might enhance any weak links so that we can better design vaccines to achieve protective immunity when vaccinating animals whose immune systems may be less than fully functional.”