Bacterial chondronecrosis with osteomyelitis -- BCO -- can cause severe lameness in modern, fast-growing broiler chickens. Currently, BCO results in condemnation of an estimated 1-2% of market age birds. Besides this huge economic loss, there are animal welfare and food safety concerns as pathogenic bacteria necrotize leg bones. However, a new study finds that feed supplementation with a plant-derived vitamin D metabolite (G-1,25[OH]2D3) during the first 28 days of grow-out can cut BCO incidence by more than half.
Vitamin D or calicferol is crucial in regulating calcium and phosphorus metabolism to support the avian skeletal system, and, with adequate exposure to sunlight, birds produce their own. However, in intensive poultry production, diets require supplementation, usually with vitamin D3 or its first metabolite (25[OH]2D3). Importantly, studies going back two decades also point to the second metabolite (1,25[OH]2D3) and its importance in bone calcification, cell growth and differentiation, endocrine regulation, and immune responses.
Modern, fast-growing broilers may be more susceptible to physical or mechanical stress in the long bones of the leg, which also can hamper their immune defense and increase their vulnerability to bacterial infection from blood-borne pathogens, particularly Staphylococcus, Escherichia, and Enterococcus species. These pathogens escape from the gastrointestinal and respiratory tracts into the blood and then colonize the bone growth plate causing BCO.
BCO-induced lameness is a transmissible disease with potentially severe symptoms including goblet gait, apathy, restricted motion, and a generally abnormal habitus or body condition and posture. Severely infected birds experience pain that can limit their ability to access feed and water. Moreover, BCO can increase food safety risks and affect meat quality. Previous studies show that in rapidly growing broilers BCO lameness rates can be as high as 19%.
The international university-industry team of researchers who authored the present study note that synthetic 1,25(OH)2D3 is commercially available. However, they point out that this synthetic metabolite is immediately released in the intestine, which confers only a short-term supply. By contrast, the dried leaves of waxy-leaf nightshade (Solanum glaucophyllum or SG) contain a glycoside metabolite analog called G-1,25(OH)2D3 that requires enzymatic cleavage prior to absorption, thus providing a longer-term supply.
The researchers reference several studies over more than a decade reporting that SG-derived G-1,25(OH)2D3 -- like synthetic 1,25(OH)2D3 -- benefits calcium homeostasis, bone health, and muscle strength. In addition, the researchers state: "The SG-derived G-1,25(OH)2D3 also induces the synthesis of antimicrobial peptides such as cathelicidins, which are essential for initial defense against pathogens and modulate the inflammatory response by upregulating the expression of IL-10 and IL-1β."
In this study, the researchers sought to determine:
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Optimum concentration of SG-derived G-1,25(OH)2D3 to reduce the incidence of BCO
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Effectiveness of early feeding (the first 28 days) versus late feeding (the last 28 days), "based on the hypothesis that strengthening the structural bone quality and immunological defense during the early growth phase of broilers would reduce their vulnerability to bacterial infections"
Using University of Arkansas poultry research facilities, the researchers assigned 1,456 day-old mixed-sex broiler chicks (Cobb 500) from Cobb-Vantress (Siloam Springs, AR) to six dietary treatment groups covering 56 days with four replicates of 56 chicks per treatment and two pens of BCO source birds for aerosol disease transmission.
The study's basal diet conformed to the breeder's recommendations, including supplemental vitamin D3, with treatments consisting of additional vitamin D supplied by G-1,25(OH)2D3 (Panbonis10 from Herbonis Animal Health GmbH, Switzerland). Treatments ranged in dosage from 0.5 to 2.0 µg/kg of the ration.
"Considering the immunomodulatory and calcemic effects of G-1,25(OH)2D3 shown in... previous studies," the researchers state, "we anticipated that supplementation... with an optimum concentration will provide significant protection against BCO lameness."
In this study, the onset of BCO in the source group began at 39 days of age and treatments of both 1.0 µg/kg for the first 28 days and 1.0 and 2.0 µg/kg for 56 days delayed BCO onset by three to four days. The lowest cumulative BCO-induced lameness resulted from the 1.0 µg/kg treatment, which decreased lameness by 53.7%.
In addition: "Feeding... 1.0 µg/kg of G-1,25(OH)2D3 for the first 28 days provided protection against lameness equal to that for the entire production cycle (56 days)."
The researchers warn that subclinical BCO remains an issue -- necropsy of "apparently healthy birds" at 56 days still showed bone lesions with a high proportion of Staphylococcus species. They also caution: "Prolonged production cycles of fast-growing broilers up to 56 days should be avoided without counter measurements to reduce the incidence of BCO."
Further investigation, they suggest, should focus on the mode of action of G-1,25(OH)2D3 in order to establish how its use early in the broiler production cycle can "enhance bone health, strengthen luminal defense, and regulate immune responses, thereby preventing bacterial leakage from the lumen."
What does this study mean for producers?
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BCO is a widespread, costly disease that develops at a subclinical level throughout grow-out even in apparently healthy broilers
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Over and above standard vitamin D3 supplementation, use of 1,25(OH)2D3 metabolites can help reduce the incidence of BCO
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G-1,25(OH)2D3 -- a Solanum glaucophyllum leaf derived glycoside metabolite analog -- provides slow-release advantages with optimal results at 1.0 µg/kg for the first 28 days of grow-out
The full paper, titled "Early 1,25-dihydroxyvitamin D3-glycosides supplementation: an efficient feeding strategy against bacterial chondronecrosis with osteomyelitis lameness in broilers assessed by using an aerosol transmission model" can be found in Applied Poultry Research and online here.
DOI: 10.1016/j.japr.2024.100440
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