The Challenge

Fatty Liver Haemorrhagic Syndrome (FLHS) can affect up to 5 per cent of hens at peak of lay and is therefore of economic significance to producers. Livers from hens that die from this disease have excessive fat accumulation and signs of internal bleeding in multiple areas. Preliminary evidence suggests that there is a difference in the rate of blood clot formation in plasma from FLHS-susceptible hens compared to plasma from normal hens.

Dr Darren Wood and his research team at the University of Guelph decided that if they could discover the cause of blood clotting abnormalities in laying hens with FLHS, then not only might it provide the industry with a way forward in managing this important disease, but it might also provide a model to study the impact of abnormal blood coagulation in other diseases where blood clotting abnormalities have also been observed.

The Research

An inbred strain of hens predisposed to FLHS (UCD-003, FLHS-susceptible) was used to characterise haemostatic and lipid profiles relative to age-matched Single Comb White Leghorn (SCWL) laying hens maintained under similar environmental and nutritional conditions.

The effect of a standard diet, as well as two additional dietary formulations, was compared in both SCWL and UCD-003 hens:

• diet 1(standard mash layer diet formulated in accordance with all the nutrient requirements of poultry with no supplement)
• diet 2 (similar to diet 1 except with higher fat content) and
• diet 3 (a 10% flax oil diet that is used commercially to enhance omega-3 fatty acid composition of eggs).

All diets were balanced for metabolizable energy, crude protein, available phosphorus, methionine and lysine. Birds were individually housed and fed experimental diets ad libitum. Feed intake was measured weekly and egg production recorded daily. Twenty-four hens of each strain were assigned to each of the three diets.

Blood samples were collected from all birds at the beginning of the trial and again after 4 and 6 weeks of feeding for analysis of haemostatic parameters and lipids. Haemostasis parameters measured included the activity of factors V, VII, X and antithrombin. Phospholipid profiles were quantified using standard procedures of lipid extraction, thin layer and gas chromatography. All birds that died spontaneously during the study were necropsied and both gross and histopathological lesions described. Samples were collected from haemorrhagic and non-haemorrhagic sites in the liver for histology. Tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, cut, and stained with H&E. At 6 weeks after initiating feeding trials, remaining birds were humanely euthanized and the degree of haemorrhage in the liver visually scored. Complete post-mortems and tissue collection performed as described were also performed.

Feed intake was similar across all diets and strains during the trial period, however egg production was overall significantly lower for the UCD-003 birds. Pre-trial blood sample results showed that activity of factors VII and X were significantly higher in UCD-003 than SCWL hens, but these differences did not persist after 4 and 6 weeks on the different diets. Antithrombin activity was not significantly different between strains or diets.

Phospholipid analysis revealed predominance of four lipids in plasma regardless of strain or diet: phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SPH) and lyso- hosphatidylcholine (Lyso-PC). However, gas chromatography suggested there were quantitative fatty acids differences with respect to strain and diet.

Nine birds died during the trial, seven UCD-003 and 2 SCWL hens. All seven UCD-003 died from FLHS, while the 2 SCWL hens died from unrelated causes. There did not appear to be a dietary effect on mortality in the UCD-003 birds.

Haemorrhage scores in UCD-003 birds that died or were necropsied at the end of the trial were significantly higher than for SCWL hens. Histologically, birds from both strains had similar liver fat content regardless of diet ingested. When haemorrhages were observed grossly, histological lesions were also found.

The Bottom Line

The researchers demonstrated that a strain of laying hens susceptible to FLHS did indeed exhibit a higher frequency of the syndrome than SCWL hens. However, other than slightly higher clotting factor activity in the UCD-003 birds, no pathologically relevant abnormalities were found with respect to the haemostatic system regardless of strain of bird or diet fed.

It appears that overt coagulation abnormalities are not the reason for haemorrhage in this syndrome.

That being said, some differences were observed in fatty acid profiles between strains and diets, which will be the subject of a subsequent project. These lipids variations may translate into cell membrane abnormalities, perhaps specifically in the liver or in thrombocytes, that contribute to the development of the syndrome. A great deal was also learned with respect to measurement of clotting factor and inhibitor activity in laying hens, which will serve as a basis for future projects.

November 2008