Relationship Between Nutrition and the Immune System in Poultry
DOUG KORVER
Department of Agricultural, Food and Nutritional Sciences
4-10 Agriculture/Forestry Centre
University of Alberta, Edmonton, AB T6G 2P5 Canada
Introduction
Nutrients play an important role in the protection of the host against invading
pathogens. Nutrient deficiencies and excesses can affect immune function, usually in a
negative manner. However, certain nutrients are capable of modulating the function of
the immune system in a targeted way through a variety of mechanisms. This paper will
discuss the effect of an immune system response on the nutritional status and needs
of the animal and some examples of the impact that specific nutrients have on immune
function.
The Chicken Immune System. Although great advances in our knowledge of poultry
nutrition has occurred in recent years, the field lags behind that of mammalian
immunology. The availability of reagents, test kits and methods in mammals such as
mice has allowed for rapid advances in the knowledge of immunity. Although chickens
cannot be thought of as “mice with feathers”, the principles, if not the exact
mechanisms can be inferred from mammalian immunology. Recent technological
advances and increases in the availability of avian reagents, and the sequencing of the
chicken genome have allowed avian immunology to begin to catch up somewhat.
However, much can be learned about the outcomes, if not exactly the processes of
avian immunity by looking to the mammalian literature.
The immune response can be divided into two basic components (Korver, 2012).
There are non-specific defenses, which protect the host by excluding pathogens, or by
creating conditions within the host which provide an inhospitable environment for a wide
range of pathogens. Barriers to entry and survival of pathogens include the skin, the
mucus coat of the GI tract, and molecules such as agglutinins, precipitins, acute-phase
proteins, lysozyme, etc. These mechanisms act non-specifically in that they are not
targeted against a specific pathogen; many different pathogens can induce similar
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responses. Once a pathogen has gained entry to the host, the initial response is an
inflammatory response. Because this response is non-specific, the effects are often
systemic within the host, and can have effects throughout the body. Fever, cachexia,
and anorexia are all examples of byproducts of the inflammatory response which have
systemic effects. The innate immune response is the first line of defense for the bird
(Erf, 2004). During the first week of life, the innate immune response of the chick is
particularly important because the other arm of immunity, the adaptive response is
functionally immature (Crhanova et al., 2011; Bar-Shira et al., 2003).
Cells involved in the non-specific response include natural killer cells, and proinflammatory cells such as macrophages, monocytes and heterophils (Andreasen et al.,
1993). The inflammatory response results in a series of behavioral, immunologic,
vascular and metabolic responses (Kogut, 2000; Gray et al., 2013). The sum of these
responses results in slowed growth rate, the loss of skeletal muscle, decreased
appetite, morbidity and possibly mortality. The mortality is often due to the effects of
the mediators of inflammation produced by the host, rather than the pathogen itself.
This is evidenced by the use of bacterial lipopolysaccharide (LPS) to induce an
inflammatory response. In this model, bacterial cell wall components mimic the effects
of bacterial infection, even though the LPS is sterile. The host recognizes the LPS as
being foreign (Kumar et al., 2013), and mounts an inflammatory response, even though
not responding would have no deleterious effect on the host. The inflammatory
response can result in dramatic decreases in productivity of animals; antibiotics appear
to work by minimizing the necessity of the inflammatory response to deal with bacteria
(Roura et al., 1992). Following an inflammatory response, animals may undergo
compensatory growth. During this time, nutrient needs of the animal may be increased.
The second aspect of the immune response is the specific immune response, in
which very specific molecules such as immunoglobulins are produced to respond to a
very specific antigen. The specific defenses employed by the host include the humoral
response (Immunoglobulins from B cells; Scott, 2004) and the cellular response (T-cell
mediated; Erf, 2004). This response is much more focused, and therefore the action of
the immune system does not tend to have a large direct effect on the host in terms of
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nutrition. As discussed previously, the nutrient needs of the cell types involved in
specific responses are minimal compared to the alterations in metabolism and demand
associated with an inflammatory response. Much research in the area of nutritionimmune function interactions is aimed at modulating immune responses to such that
specific immunity, rather than inflammation is the predominant response.
Interactions Between Nutrition And Immunity. Nutrition and immunity can each
influence the other. These interactions can be either direct or indirect, in that a
particular nutrient may have direct effect on the function of a cell trype, or the response
to a stimulus. An example of an indirect effect is selection of birds for increased growth
rate changing nutrient requirements for optimal immune function, or changing the
partitioning of nutrtients between growth processes and other metabolic functions such
as immunity.
Indirect Impact of Nutrition on Immune Response. Genetic selection of chickens
has led to drastic increases in growth rate and breast meat yield (Schmidt et al., 2009).
The increased proportion of nutrient intake devoted to growth and muscle development
can in turn led to decreased nutrients available for other physiological functions such as
immunity (Rauw et al., 1998). There appears to be a negative correlation between
growth rate in broilers and certain aspects of immunity in poultry (Yang et al., 2000;
Qureshi and Havenstein, 1994; Cheema et al., 2003)
When poultry are selected for high rates of production, it may place metabolic
stress upon the animal, and render high producing animals more prone to infectious
disease. A study was conducted to compare the effect of an experimental cellulitis
challenge model on a line of broiler chickens not selected for growth since 1957, a line
not selected since 1977, and a 1998 line of commercial broiler chickens (Inglis and
Korver, unpublished data). Because voluntary feed intake was expected to vary greatly
among the three lines, and because level of feed intake can influence immune function
(Klasing, 1988), half of the birds within each treatment were feed restricted to the feed
intake level of the 1957 broiler line. The other half of the birds within each strain were
allowed to consume feed ad libitum. When the average body weight of the birds within
each strain-feeding treatment reached approximately 1.2 to 1.4 kg, half of the birds
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within each strain-feeding treatment were injected with a strain of Escherichia coli
isolated from field cases of cellulitis. The other half of the birds in each treatment were
injected with sterile saline. Among the ad libitum-fed birds, the 1998 birds had
approximately a 10% reduction in body weight in each of the 2 weeks following E. coli
injection. The growth rate of the 1977 ad libitum-fed birds was not affected by E. coli
infection. The 1957 ad libitum-fed birds did not have reduced growth rate in the week
following infection, but in the week following the injection week, had approximately 50%
reduction. By two weeks post-injection, none of the strains had any difference in growth
rate between the infected and non-infected treatments (Figure 1).
Week
Figure 1. Changes in weekly gain for ad libitum feed treatment relative to E.coli (E)
and Saline (S) injection treatments. Injections were administered two days prior to the
body weight measurement for that week. Letters a,b and x,y denote significant
differences between injection treatments within strains (P < 0.05).
When the birds were restricted to the level of feed intake of the 1957 strain, there was a
marked difference in the effect of E. coli infection compared to the ad libitum-fed birds.
The 1957 strain when “restricted” showed a similar response to the “ad libitum” fed
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birds – approximately a 50% reduction in growth rate in the first week following the
injection week. This is not surprising because the level of feed intake was the same
between the two groups. However, the 1977 birds now had a 17% reduction in growth
rate due to E. coli infection in the week following the infection week. The 1998 birds
had only a 3% reduction in growth rate due to infection (Figure 2).
week
Figure 2. Changes in weekly gain for restricted-fed birds relative to E.coli (E) and
saline (S) injection treatment. Injections were administered two days prior to the body
weight measurement for that week. Letters a,b denote significant differences between
injection treatments within and between strains (P < 0.05).
Interleukin-1 (IL-1) is a cytokine that regulates fever, cachexia, and many other
aspects of systemic inflammation. In a similar experiment, the 1998 broiler chicken line
had T cells with a substantially greater responsiveness to IL-1 than either of the
unselected lines (Figure 3).
These results suggest that in the past, genetic selection for growth rate may
have increased susceptibility to infectious disease, and that much of this effect was
associated with the increase in feed intake of modern commercial broiler chickens. The
modern lines of broiler chickens had a much higher responsiveness to IL-1, indicating
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that the balance of systemic inflammation following a bacterial challenge has changed
with genetic selection for performance.
Figure 3. T-cell proliferation index for T-cells harvested from birds from each strain in
response to stimulation with cytokines produced by an avian macrophage line (HD11)
stimulation with heat-killed Staphylococcus aureus. Letters a,b denote significant
differences between strains (P < 0.05).
The good news for the poultry industry is that it is possible to select for both
increased growth rate and increased indices of immune function. The primary poultry
breeders have to incorporated aspects of health and livability as well as productivity and
efficiency into their selection criteria (D. Emmerson, Aviagen Inc., personal
communication). This has resulted in continued increases in productivity and efficiency,
as well as reduced incidence of metabolic and infectious disease in modern birds.
Since 1998, infectious diseases such as cellulitis, and metabolic diseases such as
ascites, skeletal defects and sudden death syndrome in commercial broilers have
decreased substantially, even as growth rate and efficiency of modern broilers
continues to increase year by year.
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Direct Nutritional Modulation of Immune Function. Numerous studies over the
years have been conducted investigating the influence of various nutrients on different
aspects of immune function. When looking at the literature, it is important to keep
several things in mind. The concept of immunomodulation can be defined as:
Supplementation of that nutrient, beyond the requirements for growth, but
below the toxic level, alter some aspect of immune function
This would include nutrients for which there is no specific requirement (e. g.
canthaxanthin, conjugated linoleic acid, etc.). Many studies investigating purported
“immunomodulatory” nutrients have supplemented these nutrients at levels well below
or in excess of requirements, and interpret changes in some aspect of immune function
as “immunomodulation”. However, caution must be taken when evaluating these
studies, because they generally indicate that “optimum” immune function can be
obtained when the nutrient is supplemented at the levels likely already being fed by
industry. Therefore, there is no added benefit to adding more of a particular nutrient to
an already sufficient level in the diet. For there to be a benefit, the industry needs
information on nutrients that confer an additional benefit to a nutritionally complete diet.
The purpose of this paper is not to give an exhaustive review of all of the
nutrients that can be used to modulate immunity in poultry. Rather, specific examples
will be used to illustrate the ways in which some specific nutrients can be used by the
industry. It is important to realize that the two arms of immunity (innate and acquired)
work together to protect the host, are in balance with one another, and that very often
factors that increase the function of one arm of the immune system will have the
opposite effect on the other arm (Anderson and Fritsche, 2002).
Fatty Acids. One of the most widely studied classes of immunomodulatory nutrients in
poultry nutrition are the fatty acids. Although feeding n-3 polyunsaturated fatty acids as
fish oil to chickens increased the expression of pro-inflammatory cytokines following an
inflammatory challenge (Sijben et al., 2003), systemic effects of inflammation such as
reduced feed intake and growth rate are suppressed by dietary fish oil in chickens
(Korver et al., 1997).
Feeding of n-3 polyunsaturated fatty acids (flax oil or fish oil)
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increased anti-bovine serum albumin antibodies in the yolks of laying hens relative to
hens fed animal fat (Selvaraj and Cherian, 2004). However, Sijben et al (2001) reported
that linolenic acid increased anti-keyhole limpet hemocyanin antibodies, but only when
fed with low, rather than high levels of linoleic acid. Conversely, in the same study,
antibodies against Mycobacterium butyricum were increased when linolenic acid was
fed at high, but not low levels of linoleic acid. Therefore, dietary n-3 fatty acids may
have a net positive effect on poultry production because they may move the immune
response towards a more directed, localized response while reducing the systemic
effects. Although n-3 fatty acids are clearly immunomodulatory, the exact response to
expect may be dependent on the type of n-3 fatty acid (long-chain vs medium chain),
and the fatty acid composition of the rest of the diet.
Another immunomodulatory fatty acid is conjugated linoleic acid (CLA; Cook,
1993). Broiler chickens fed increasing levels of CLA (up to 1% of the diet) had
increased levels of lymphocyte proliferation following stimulation with concanavalin A or
lipopolysaccharide, reduced serum prostaglandin and peripheral blood mononuclear
cell numbers, as well as increased primary and secondary antibody responses to sheep
red blood cells (Zhang et al., 2005b). Thus, CLA appears to increase cell-mediated and
humoral immunity, while decreasing aspects of inflammation. This latter observation is
supported by Cook et al., (1993), who reported that chicks fed 0.5% of CLA had
reduced growth suppression following injection of E. coli lipopolysaccharide. Inclusion
of higher levels of CLA (up to 10% of the diet) did not have similar effects (Zhang et al.,
2005a).
Minerals. In reviewing the literature, many minerals have been reported to affect
immune function in chicks. There is clearly a relationship between inflammation and
immunity, as iron and zinc are withdrawn from the blood and stored in tissues such as
the liver and spleen by the host following infection as a means of limiting pathogen
growth (Blackmore et al., 2006). Conversely, copper levels in plasma increase
following an inflammatory challenge (Blackmore et al., 2006) likely because of copper’s
antibacterial effects. However, these minerals are not likely good candidates as
immunomodulators because the effects of changes in dietary levels on immune
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function are generally only observed when fed at deficient or excessive levels relative to
typical commercial levels of supplementation. In addition, the response to the deficient
or excessive levels in terms of immune function would generally be considered
detrimental to the health of the bird.
Selenium is a mineral that may potentially be immunomodulatory. Although a
deficiency of Se reduces killing efficiency of phagocytic cells (Arthur et al., 2003), there
is some indication that supplementation of Se at levels up to 400 μg/kg diet increased
lymphocyte proliferation ratio in a linear fashion (Rao et al., 2013), The effect of Se on
immune function may be mediated through its role in antioxidant protection – with
greater antioxidant protection, the host can increase production of the reactive oxygen
species (ROS) used by the immune system to destroy invading organisms (Huang et
al., 2012.
Vitamins and Related Compounds. Both vitamin E and vitamin A are involved in
tissue antioxidant protection (Surai, 1998; 2000). As such, they may play a similar role
to selenium in allowing expression of increased levels of ROS by the immune system
by offering increased protection of the bird’s own cells against these highly reactive
compounds. Within a range of supplementation, vitamin A or vitamin E can increase
antibody production and T cell proliferation, although excesses of vitamin A can reduce
resistance to E. coli infection (Sklan et al., 1994, Friedman et al., 1991). Similarly,
increasing vitamin E to broiler chicks from 0 to 50 IU/kg of feed resulted in increasing
antibody titres to infectious bronchitis virus, but additional supplementation had no
effect (Leshchinsky and Klasing, 2001). In fact, antibody response to sheep red blood
cells decreased as vitamin E was increased from 50 IU/kg to 100 and 200 IU/kg
(Leshchinsky and Klasing, 2001).
Maternal or broiler supplementation of lutein resulted in chicks with reduced
systemic effects of inflammation following Salmonella typhimurium lipopolysaccharide
injection (Koutsos et al. 2006) Dietary lutein increased broiler secondary antibody
response to infections bronchitis virus vaccination (Bedecarrats and Leeson, 2006).
Other carotenoids that may influence immune function in poultry include canthaxanthin
(Zhao et al., 1998), astaxanthin (Waldenstedt et al., 2003) and curcumin (Rajput et al.,
9
2013), among others.
Conclusions. The immune system is essential to survival of an animal when there is a
risk of exposure to potential pathogens. In the context of poultry production, this means
that reduced or eliminated use of growth-promoting antibiotics in poultry production will
force a greater reliance on the bird’s immune system to prevent bacterial disease. The
innate and acquired arms of the immune system work together to protect the host.
Each of these aspects of immunity can be manipulated by nutrients in the diet. Many
nutrients can cause reduced immune function when present at deficient or excessive
levels. However, the concept of “nutritional immunomodulation” to increase bird health
requires that supplementation of a particular nutrient, between the range of minimum
requirement and toxicity, have a specific, predictable, and in most cases, beneficial
effect on bird health or productivity. Several nutrients for which there is no established
requirement (e. g. n-3 polyunsaturated fatty acids, carotenoid pigments, etc.) can also
be used to achieve nutritional immunomodulation. The innate and acquired immune
systems are in balance with each other, and communicate to coordinate an immune
response. Up-regulating one side of the immune system often down-regulates the
other side of the immune system. Therefore, any plan to use nutritional
immunomodulation must be done with an awareness of the most likely immune
challenges the bird will face, and an understanding of the potential negative
consequences.
Broiler chickens have been selected for rapid growth rate, and in the past, this
may have led to an inadvertent selection against immune function, particularly
inflammation. However, more recent genetic selection programs by primary breeding
companies have taken a more balanced approach, and the health and livability of the
birds have become important selection criteria in addition to growth, meat yield, and
efficiency.
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