How could you pick out the keeners in high school? They even studied for a blood test. Maybe they were onto something, though, as today, scientists seeking to improve disease resilience in pigs are studying a particular blood test as part of their cutting-edge research.
“Disease is a huge concern in the pig industry today,” said Xuechun Bai, a PhD student in the Faculty of Agricultural, Life & Environmental Sciences at the University of Alberta. “Disease affects growth rate, impacts animal welfare and causes significant economic losses; just look at China and African Swine Fever as a prime example.”
Disease resilience affects an animal’s ability to maintain growth and performance in spite of infection by re-allocating its resources between immunity and productivity. To make genetic improvements for resilience, scientists need to identify predictors obtained in high health nucleus herds where breeding animals are selected.
“It is very challenging to select for resilience, as it’s a complex trait that is hard to characterize,” said Bai. “Resilience is comprised of many biological functions such as immune response, growth performance and how quickly an animal recovers from an infection challenge. Consequently, instead of directly selecting for resilience, we are trying to find genetic markers that are easy to measure and can help us in ultimately targeting resilience.”
Tuning in to the CBC
One such marker that may be useful for identifying more resilient pigs is a complete blood count (CBC), a blood test that evaluates overall health in both humans and animals and can detect a wide range of disorders. It measures several components of blood including the concentration and relative proportion of circulating red blood cells, white blood cells and platelets.
“Platelets are mainly involved in clotting, while red blood cells carry oxygen to tissues and organs in the body and white blood cells fight against infectious agents,” said Bai. “We want to look at all three and evaluate them as biomarkers for disease resilience.”
To that end, data were collected from 2593 pigs that went through a Natural Disease Challenge Model. One blood sample for CBCs was taken in the quarantine nursery, another in the polymicrobial disease challenge nursery and the third in the grow-finish barn. The pigs were classified based on their growth performance and individual treatment records through to finish.
“We classified the pigs into four groups from most resilient to most susceptible in terms of disease response. The most resilient group had the highest growth rate in the test station and the lowest individual treatment counts. In the moderate group, pigs showed average growth rates, followed by the susceptible group and, finally, the animals that succumbed to disease.”
Though CBCs measured in blood from healthy pigs prior to entering the Natural Disease Challenge Model showed no differences between resilient and susceptible pigs, resilient animals exhibited a significantly greater increase in lymphocytes (one of the five white blood cell types) at the early stages of infection, and greater increases in hemoglobin at the late stage of infection.
As well, neutrophils – the most plentiful type of white blood cell in the body and the one that usually leads the immune system’s response – in resilient animals showed a tendency for a reduction during the late stage of infection.
“These results suggest that CBC traits could provide an indication of a change in resource allocation in response to infection,” said Bai. “We would expect that resilient animals should allocate more resources towards immunity during the early stages of infection and are primed to initiate a faster adaptive immune response to help limit that infection, resolve inflammation and recover more quickly in order to maintain high rates of production. CBC traits were heritable and genetically correlated with growth and treatment, which may indicate the potential to develop CBC as a predictor for the selection of resilience among breeding animals.”
Given the returns on selecting for disease resilience in pigs, which would result in better health, greater animal welfare, more production and less use of antibiotics, it’s no wonder scientists are burning the midnight oil to find success.
Meanwhile, those high school keeners are back home for a late-night cram session: Big blood test tomorrow.