The gastrointestinal system of a chicken can have a major influence on the bird’s overall health and productivity in ways that stretch well beyond the gut. Though a lot remains to be discovered about the many connections between the gastrointestinal tract and other internal systems, increasing scientific knowledge of costly bone and joint disorders — including one commonly called “kinky back” — is helping researchers develop products to enable producers to minimize economic and flock-health damage through management and preventative measures.
Spondylolisthesis, or kinky back, is a disorder that exemplifies the connection between gut health and physiological well-being in broiler chickens, and what happens when environmental stress and invasive bacteria disrupt that connection. It’s the infection of Enterococcus cecorum that causes the development of abscesses in the bone tissue of a chicken’s fifth thoracic vertebrae. Those abscesses cause the development of a bulge in vertebral tissue — hence the name — that pushes on the spinal column, often leading to a pinching of the spinal cord that can immobilize the bird.
As with many bone and joint issues in poultry, kinky back prevents birds from consuming feed and water and often makes the affected animal susceptible to damage from other birds. Ultimately, the bird’s own immune system is the cause for much of the damage initiated by kinky back and other bone and joint diseases, according to Charles Hofacre, longtime poultry veterinarian and president of the Southern Poultry Research Center in Athens, Georgia.
“The fifth thoracic vertebrae in a chicken is the only movable one, since the other four are fused. For whatever reason, Enterococcus cecorum likes to target that vertebrae, where it causes instability. It’s like a ruptured disc in a human being,” Hofacre said. “The bird’s body is trying to fight that infection with pus and fluid that tries to chew up the bacteria, but it chews up some of the bone and other tissue. The abscess is the purulent material and cell debris that pushes out and pinches the spinal cord.”
The origins of bone and joint infections like kinky back can be directly traced to the gastrointestinal tract. When a bird experiences stress, for instance, the gut may become compromised and tight junctions in the epithelial tissue lining the gut, may loosen. This enables any contaminants (e.g. pathogens) present in feed and water that would normally pass through the digestive system, to enter other internal systems.
If the bacteria enter a chicken’s circulatory or skeletal system, more extensive physical damage can be inflicted. In this way, there’s a direct connection between sometimes seemingly minor environmental stressors and systemic health issues connected by toxins and bacteria that are omnipresent on most poultry farms.
“Things like heat and cold stress can result in release of these cellular communication chemicals between cells, and that will cause leakage and widening of those tight junctions. It’s not just a pathogen or mycotoxins, but all kinds of things can do that,” Hofacre said. “A broiler eats every 3-4 hours. It will get up to eat, drink, sit back down then do it again a few hours later. That's called steady-state eating. If it misses a meal or two, you can physically see mucous building up in the intestine, and it will be sloughing epithelial cells. When the intestinal flora start to get sloughed or flushed, and the intestinal cells start producing more mucous, it becomes a problem. If something as small as just a disruption in a steady-state eating pattern can change the gut flora, it can result in a greater propensity to getting more bacteria into the bloodstream.”
Probiotics are a common way of addressing the stressors that promote the movement of harmful bacteria into places like the circulatory system where the bacteria can localize or, in the case of kinky back, skeletal systems. They’re microorganisms comprising proteins and bacteria that work by killing harmful invasive bacteria and promoting cellular immunity. The efficacy of each probiotic depends on the bacterial makeup of a healthy bird’s gut and the antibacterial function of the compound that’s added to a feed or water source. Sometimes a probiotic’s function is to bolster the health of gut tissue by helping balance necessary bacteria, while in other cases, it functions as a bacteriocin and overcomes potential gastrointestinal tissue weakening by targeting and removing harmful bacteria.
Just as their functions vary widely across different birds, so too does their efficacy. It’s one of the reasons poultry health researchers continue to work to determine which probiotics will be most effective.
“We don’t know how all probiotics work. In some instances, I’ve seen them work wonderfully, then you take them to the next barn or farm and they don’t work at all. It’s partially due to what’s really stimulating the gut problem and bacterial imbalance, which can vary from one farm to the next. Right now, we’re working on finding probiotics that can work more broadly and repeatedly against certain bacteria,” Hofacre said. “We already know certain probiotics work well against gram-positives like Clostridium and gram-negatives like Salmonella.”
Ultimately, a combination of the right products and prudent management remain the key combination in controlling diseases caused by stressors and other gut health challenges. Maintaining a clean environment; feeding clean, quality feed; and adjusting management practices to minimize environmental stress are examples of components of a strong strategy to help prevent negative impacts to health and performance.
Adding a product like Kemin’s proprietary CLOSTAT® (Bacillus subtilis PB6) can also help prevent pathogenic bacteria such as Clostridia from flourishing in the gastrointestinal system and entering other internal systems when birds are stressed. Additionally, adding a product such as ButiPEARL™ Z (encapsulated butyric acid and zinc) may be useful in strengthening the gut barrier by upregulating proteins associated with tight junction formation. However, these are just some aspects of maintaining a healthy gut. A lot remains to be learned about the interactions between stress, gut health, immunity and other systemic functions.
“While some products work fine, the whole thing is more of an animal husbandry issue, and there’s not a single generic solution across the board,” Hofacre said. “We understand what triggers diseases like kinky back better today than ever before, but we can’t say that about all disorders, and there’s no one-size-fits-all solution. We're just really scratching the surface on understanding the interaction of all the different bacteria in the gut and how they interact with each other and the host."
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