ARTICLE PUBLISHED IN ALL ABOUT FEED. Volume 39, No. 5, 2023
While modern broilers have been selectively bred for superior performance in terms of feed efficiency, growth rate, and meat yield, producers often overlook that this higher level of performance coincides with an increase in general metabolic, intestinal and immune stress. Replenishing broilers with supplemental dietary selenium (Se), in the form of hydroxy-selenomethionine (OH-SeMet), can help resolve these pressures.
When supplementing Se into the feed, it is important to consider both the source and form of Se so as to ensure that the Se is effectively absorbed, stored and utilized by the broiler in times of need.
While layer birds are more like long distance runners, broilers are like sprinters. In about 6 weeks, the birds’ feed intake and growth rate increase. With this high performance, there is an increase their oxidative metabolism and an excessive production of free radical metabolites at the cellular level. These metabolites are extremely reactive, and in turn damage biologically relevant molecules such as DNA, proteins, carbohydrates, and lipids in the cells when they accumulate. An accumulation of these metabolites leads to what is called an imbalanced redox state, which is also known as oxidative stress. Oxidative stress will induce a wide range of problems at the cellular level, which in turn will have a direct impact on health, in terms of compromised immunity, inflammation, impaired gut health, etc. and overall animal performance.
Redox balance refers to the ability of the body to maintain a dynamic equilibrium between the production of free radical molecules and the antioxidant system’s activities that mitigate them. In contrary to the general thinking, free radicals are not all bad, they are essential signaling molecules that activate response pathways in and between cells throughout the body, such as the immune system. It is true that an overproduction of free radicals, without the body’s ability to maintain a balance between synthesis and inactivation of the radicals, will often exacerbate negative physiological responses, thereby compromising cellular health, function, immunity, and animal performance.
The redox balance is extra pressured by an increasing number of challenges that the modern broiler must cope with, such as heat stress, high stocking density, reduced use of antibiotics, etc. Challenges as such require extra attention to management and nutritional solutions to keep diseases under control and birds in a high health status.
Several antioxidants are essential to keep the redox balance functioning such as: vitamins, selenium (Se), carotenoids, flavonoids, etc. Among these, Se is a critical part of the body’s antioxidant defense, as it is incorporated into selenoproteins that directly and indirectly support the various antioxidant systems throughout the body, thereby counteracting the effects of oxidative stress.
While supplementation of Se into broiler feed has been a standard practice since 1974, it has become much more important for modern broiler production. Selenium can be supplemented either as an inorganic form (sodium selenite, selenate) or two organic forms: one from fermentation (i.e. seleno-yeast) or pure, chemically synthesized forms of organic Se (i.e. SeMet or hydroxy-selenomethionine; OH-SeMet). The inorganic Se sources are known to have low bio-efficacy, while the organic sources are known to have higher bio-efficacy. The difference between the sources and their bio-efficacy is driven by their SeMet content, as it is the only form of Se that can be stored in the body, ultimately serving as an assurance/ insurance policy that can be readily mobilized by the bird in moments of stress.
Inorganic Se is adequate to support normal cellular functions under non-stressful conditions; however, during stress, two key things take place: 1. The requirement for selenoproteins increases and 2. The broiler’s feed intake decreases/ ceases. To satisfy the body’s need for Se as selenoprotein synthesis is ramped up, it is essential that body’s reserves of SeMet are built up safely and to a meaningful level. The buildup of SeMet, as mentioned before, allows the body to meet its own Se requirement for selenoprotein synthesis. Without SeMet reserves, selenoprotein synthesis is significantly restricted, which means the antioxidative machinery that fights oxidative stress is unable to work efficiently. This body’s SeMet reserve can be equated to an insurance/ assurance policy that can be mobilized and used ‘on demand’ by the broiler as needed.
Several commercial and controlled broiler studies, under challenge, have confirmed that when pure organic Se in the form of OH-SeMet (Selisseo®, Adisseo) is fed, selenoprotein synthesis, redox and immune status, and performance are maximized when compared to inorganic or seleno-yeast Se sources.
A recent study published by Sun et al (2021) delved into the efficacy of OH-SeMet in broilers under challenging conditions (high stocking density and heat stress) in China. In the experiment, Se was supplemented at 0.3 ppm either from OH-SeMet, sodium selenite (SS) or seleno-yeast (SY). After 6 weeks on the experimental treatments, OH-SeMet enhanced the Se concentration in the pectoral muscle by 139% compared to SS and 78% compared to SY. The broilers fed the two organic forms of Se, and in particular those fed OH-SeMet, showed a better intestinal morphology as indicated by an increased villus height/crypt depth ratio in the duodenum, jejunum and ileum (Figure 1).
Figure 1 – Effects of different sources of Se on gut morphology, gut integrity, and immune response
Furthermore, organic sources, specially OH-SeMet, strengthened the gut barrier (Figure 1), thanks to an increase in key tight junction (TJ) proteins and lower intestinal paracellular permeability in the gut, as reflected by a lower LPS presence in the serum (Figure 1). The modulation of the immune system was also impacted when feeding different sources of Se. The presence of the anti-inflammatory cytokine IL-10 increased to OH-SeMet compared to the other sources. On the other hand, pro-inflammatory cytokine IL-6 levels were lower when organic sources were fed compared to SS (Figure 1). Immunoglobulins (Ig), important players of the immune system, were also affected by the Se source: IgG, the major immunoglobulin present in serum, increased when OH-SeMet was fed compared to the other sources, whereas a significant decrease in IgA was detected. The lower levels of IgA in the serum reflect the increased intestinal permeability as this immunoglobulin is mainly found in the gut mucosa. A better maintenance of the immune response and in gut integrity reflected the significant improvement in feed conversion (-3 pts for OH-SeMet compared to SS). The OH-SeMet was not only better for maintaining an optimal FCR but also resulted in a numerically higher body weight gain (+57g and +59g compared to SS and SY respectively; Table 1).
Table 1 – Performance results of broilers fed different Se sources (d1-42).
The efficacy of OH-SeMet has also been confirmed in commercial field trials. For instance, a recent field trial in the US, which focused on broiler growth took place under antibiotic-free (ABF) grow out conditions. The setup for the 0 and 47 day study allowed for a collection of data throughout the houses, and pens that were set up within the commercial houses. The birds received either a diet supplemented with ¼ SS + ¾ SY or ¼ SS + ¾ OH-SeMet. The results between the house and pens agreed very well with each other, demonstrating that growth performance is improved when birds consume OH-SeMet-supplemented feeds. Birds fed the OH-SeMet had a numerical improvement in final body weight (+70g) and an adjusted 2 to 4 points improvement in FCR across the pen and house setup (Figure 2).
Figure 2 – House and pen data regarding body weight and mortality corrected FCR to 3.42kg
Broiler health, growth, and productivity are largely dependent on the balance between the incredibly high rate of its metabolism, the stressors it encounters, and its ability to neutralize the highly reactive and destructive metabolites that are generated through those processes.
Supplementation of organic Se, in the form of OH-SeMet, allows the broiler to build a significant level of Se in its tissues. When the tissue Se reserve status is high under challenging conditions, with oxidative stress, the broiler is more equipped to get back to a normal oxidant balance by stabilizing normal cellular processes throughout the bird. This will result in normal metabolism, more efficient immune responses, higher gut integrity, and ultimately better performance. The efficacy and strong results of OH-SeMet confirms that source and form of Se matters for the sprinters of the poultry industry: the modern broiler.
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