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Is there a silent killer in your henhouse?

Fatty Liver Syndrome in Laying Hens

When fatty liver syndrome (FLS) strikes, your flock is about 70–85 % peak egg production. You are working hard to reach peak egg production but, instead, you note a reduced performance of your hens and reduced egg production and egg quality. In some cases, the signs are obvious—chronic appetite loss, depression, overweight birds, decreased movement, and pale combs—but sometimes, the only sign something is amiss in your flock is the sporadic death of your hens. 

A laying hen approaching peak production has high energy needs and, when consuming high-energy diets, will deposit the excess energy as fat in the abdomen, subcutaneous, kidneys, base of the heart, intestine, and stomach muscle. Most importantly, however, fat is deposited in the liver and around the oviduct. Fatty deposits in the liver cause the liver to become soft and easily damaged. Furthermore, the fat deposits around the oviduct may cause rupture of the liver and internal bleeding during egg laying. In other words, there are both metabolic and physical stresses that are associated with egg laying that can induce the final haemorrhage. The rupture of the liver is the progression of FLS into fatty liver haemorrhagic syndrome. 

A multifactorial problem 

Fatty liver syndrome is very much a multifactorial syndrome for which several risk factors have been described in addition to a surplus of energy intake. The hormone estradiol has been implicated in FLS. Associated with sexual maturity, this hormone stimulates the liver to increase fat storage for egg yolk synthesis. Consequently, as egg production begins, the liver size increases dramatically in response to estrogen levels.  

The inflammation response has also been implicated as one of the initiators of fatty liver hemorrhagic syndrome. Higher levels of inflammatory markers have been reported in birds with experimentally induced FLS. In commercial situations, the inflammatory reaction causing this transition can be caused by other factors, including nutritional and environmental factors.  

Fatty liver syndrome is often described in laying hens with limited movement and maybe associated with the type of housing system. In one study, it was reported that, although the overall mortality rate was not different between the housing systems, the cause of death was different. In caged laying hens, 74 % of hens died from FLS, but in birds in alternate housing systems, only 0–5 % of dead hens were diagnosed with the condition.  

Moreover, despite the change in husbandry practices of much of the egg industry, cage production systems continue to be the predominant system for housing laying hens in many countries making this syndrome a major potential threat to laying flocks. Indeed, it has been recently estimated that more than 90 % of egg production in China, Japan, and the US was from caged hens and in Turkey, India, Russia, and Mexico, this number was 100 %. 

It is known that the highest incidence of FLS occurs during warm periods. In general, higher ambient temperatures reduce energy requirements, which leads to a positive energy balance. Coupled with the already increased energy balance of a laying hen being fed for peak production, increased environmental temperatures only intensify the development of the disease. 

Additionally, birds rely on evaporative cooling during respiration to regulate body temperature. Unfortunately, the increased abdominal fat in these hens can interfere with normal breathing and cooling, making these birds more prone to both heat stroke and liver rupture from FLS. We can thus predict that flocks performing in warm climate regions may be even more susceptible to this syndrome. As it becomes increasingly evident that extreme temperatures are increasing across the globe, it seems inevitable that exploring solutions for FLS is becoming increasingly necessary. 

Subclinical but costly 

Fatty liver syndrome is often undiagnosed in laying hens. Mortality is usually 3–5 %—although it can be higher—but it is important to remember that death only occurs in extreme cases following massive liver haemorrhage. This suggests that a considerable number of hens within a flock might suffer from sub-acute and chronic FLS. However, if FLS does not cause evident morbidity or an apparent drop in productivity, should it be addressed? If, in live animals it is difficult to distinguish the affected from healthy hens and there are no available diagnostic tests such that the syndrome is often overlooked, is FLS harmful to production? 

The answer is, of course, not as straight forward as it would appear on the surface. First, there is an association between FLS and eggshell quality. One important function of the liver is the activation of vitamin D into its active form—vitamin D3. It has been reported that calcium levels in the blood of hens with FLS are elevated, suggesting interference with the formation of active vitamin D, vital in the eggshell formation process. Vitamin D3 is required for normal calcium absorption. An inadequate amount of Vitamin D3 quickly induces calcium deficiency and a drop in eggshell weight, resulting in weaker and thinner shells. It has been suggested that downgraded eggs account for 3.5 to 12% of all eggs, which can increase toward the end of the laying cycle. In addition to eggshell quality, the chronic form of FLS may cause a drop in egg production, but little or no change in mortality; such hens may exhibit reproductive dysfunction. 

Prevention is key 

Since FLS can easily go unnoticed, as a “silent killer”, one of the most important aspects for prevention is monitoring for risk factors and signs. Feed intake should be monitored, along with increases in body weights and mortality and decreases in egg production. Routine body weight and uniformity checks can help reveal development of excess body weight. Access to established diagnostic tests is not always accessible. Therefore, in many cases today, necropsies are still required for definitive diagnosis. This can make it particularly tricky to identify the problem in a flock with no obvious signs.  

Another strategy to prevent FLS is the careful preparation of the diet. The diet should be formulated based on the species and egg production rate, so that energy to production ratio can be controlled within a reasonable range. The reduction of dietary energy intake, such as the increase of some fat rich in linoleic acid and reducing carbohydrate can reduce the incidence of this disease. This is because supplemental fat decreases the synthesis of new fat, so the liver is under less stress to produce fat for the yolk. Overall, this reduces the metabolic burden on the liver. 

Feed enough energy to sustain the birds while optimizing production, but not more. Maximizing the energy intake in the initial period of lay is essential to support productivity; however, energy requirements will decrease through the lay period as production decreases. As such, it may be necessary to reduce diet density to avoid birds gaining excess weight. Indeed, the ratio of metabolic energy to protein in the feed varies with temperature and egg laying rate. For example, at elevated temperatures, the energy to protein ratio is decreased by 10 %. Other prevention strategies include providing suitable living space, controlling the ambient temperature, and reducing bird stress. 

Complex but not complicated solutions 

In addition to feeding and husbandry strategies, there are solutions to help support the high producing laying hen. The tipping point for subclinical FLS to progress to deadly fatty liver hemorrhagic syndrome often goes undetected until it is too late. Therefore, fortifying the flock before this becomes a problem is essential. In-feed supplementation has been the norm for many years to support birds against FLS. However, with fluctuating and sporadic extreme temperature events and increased gut stress during feed changes, a simpler solution is needed.  

At Biochem, we have developed concepts that are formulated to holistically support healthy liver fat storage and mobilization and to support the bird during times of stress—such as heat stress. As these concepts are designed to be added in the drinking water, they are easily and readily applied with precision. These are uncomplicated solutions that can prove valuable in the overall health and welfare of the flock. 

Fatty liver syndrome remains an unresolved malady in laying hens and both the acute and chronic forms of the disease are a significant source of loss for egg producers. We have years of experience developing on-farm solutions to support your production operation. Contact us to find out how we can develop a program together to help you support your high producing laying hens.