Disease challenges drastically diminish pork production productivity and efficiency, and have substantial negative economic impacts on producers. When a pig’s immune system is activated to fight disease, it requires extra energy that is then no longer available for growth. This means that either the pig must consume more feed to maintain similar levels of growth, or less growth is achieved at similar intakes. Often, immune challenges drastically decrease feed intake, which compounds the energy limitation problem. All of these scenarios mean decreased production efficiency, slower barn throughput and economic losses.
Immune system activation can partition energy and nutrients away from productive growth, but clear relationships between immune responses and the direction and magnitude of energy partitioning responses have yet to be clarified. The objective of this experiment from a team of researchers at Iowa State University was to determine how lipopolysaccharide (LPS) immune stimulation affects maintenance energy requirements through changes in serum immune parameters, digestibility, growth performance, nitrogen and energy balance. LPS contains E. coli cell fragments that “trick” the immune system into thinking bacteria are present.
In this study, 30 nursery pigs were assigned to either a control treatment with basal corn, soybean meal and soybean hulls diet; an enzyme treatment with basal diet plus beta-mannanase; or an immune system stimulation treatment with basal diet plus beta-mannanase, challenged with repeated, increasing doses of E. coli LPS. The experiment consisted of a 10-day adaptation, five days of digestibility and nitrogen balance measurements, followed by 36 hours of heat production measurements. The immune stimulation treatment induced fever, elevated serum proinflammatory cytokines (tumour necrosis factor alpha, IL-6, IL-1beta) and decreased white blood cell concentrations; thus, it was confirmed that the pig’s immune system was behaving as it would in a disease outbreak.
Nitrogen balance and nutrient digestibility was similar among all treatments, but immune stimulation increased total heat production by 17% and estimated maintenance energy requirements by 24% (refer to graph). This resulted in a 27% decrease in fat deposition and 26% average daily gain decrease. Immune stimulation increased energy partitioning to the immune system by 24%, which limited energy available for fat deposition and weight gain. These results quantify the magnitude of energy shift away from growth during a disease challenge; this information can be used to develop more effective feeding strategies to improve pig performance during disease outbreaks. Note that these pigs were limit-fed, so that all pigs, irrespective of treatment ate the same amount of feed. This approach is necessary to measure maintenance energy. However, when pigs in a barn get sick, they also eat less feed, which compounds the problem of less energy being available for growth.
This research expands on the understanding of how immune challenges change energy metabolism in the pig and may inform more effective feeding strategies to mitigate negative impacts of disease. Furthermore, understanding how much extra energy sick pigs require can help to put an economic value on the cost of disease and, more importantly, the value of maintaining a high-health herd.
The results of this experiment support the knowledge that there is great economic importance in maintaining a healthy population. Any energy that is partitioned toward an immune response is not available for growth. Thus, health challenges can impair production efficiency. Decreased growth rate and impaired efficiency increase days to market and reduce profitability.
Researchers: Nichole F. Huntley and John F. Patience, Department of Animal Science, Iowa State University; and C. Martin Nyachoti, Department of Animal Science, University of Manitoba. For more information, contact Patience at 515-509-1756 or [email protected]