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Figure 1A: Abnormal liver from a layer chicken infected with SLD. Note excess pericardial fluid, hepatomegaly and fibrin at the base of the liver lobe.
Figure 1B: Hyperaemic ova of a layer that died of SLD.
Table 1: SLD stage 1 trial data.
Extra labour costs were not calculated in these fig- ures, but feed savings of dead hens were.
Manure samples from rearing flocks before and after vaccination were re- peatedly tested as negative for c hepaticus via PCR.
The vaccine was found to be robust as no vaccinated hens broke with SLD dur- ing the remainder of flock life.
All these layer sites were endemically infected with SLD, where hens predict- ably break with the disease at or soon after peak of lay.
Spotty liver disease description and effects on industry
SPOTTY liver disease has occurred for decades in Australia and other countries over the world, with campylobacter he- paticus being the bacteria identified as the causal agent.
$0.5 per hen in the flock to $4.29 per hen in the flock.
undertake vaccine trials against SLD in Australia. Field vaccine trials stage 1
gauge any differences in production.
ing sheds were given the above-mentioned autoge- nous c hepaticus SLD vac- cine from Tréidlia Biovet Laboratory at eight and 12 weeks of age.
The disease appears to largely affect layer chick- ens of free-range or barn systems.
The largest and most sig- nificant factor identified af- fecting cost of the disease was mortality – as dead hens obviously don’t lay eggs for the rest of flock life.
Half a flock of 40,000 rearing pullets were vac- cinated twice – 12 and 16 weeks of age – via intra- muscular injection with a killed autogenous c hepat- icus vaccine supplied by Tréidlia Biovet Laboratory.
Each of the vaccinated halves of the sheds had less mortality and egg pro- duction decrease than the unvaccinated halves – see Table 1.
As per usual protocol, these pullets were trans- ferred to free-range layer sites at 16 weeks of age.
Spotty liver disease can affect any age flock during its first occurrence on a farm, though once estab- lished on a farm it occurs almost exclusively in flocks at peak of lay.
Other factors calculated in cost of the disease were eggs lost during the egg production drop, costs of in-feed or in-water addi- tives trialled to prevent SLD and any treatments given to the flock.
This was repeated in two further rearing flocks.
The mortality and egg production drop results were significantly different for flock three, in the vac- cine’s favour.
Five x 40,000 hen flocks were transferred to layer siteA–usedinStage1 of trials – three x 11,000 hen flocks were transferred to layer site B, and three x 17,000 hen flocks were transferred to layer site C.
Egg production can de- crease in the flock by 10- 35 percent, and mortality increase by 10-15 percent, though these extremes are not always the case.
Interestingly, across the vast number of in-feed and in-water additives trialled – probiotics, prebiotics, acids, clays, essential oils – none prevented or significantly reduced the mortality asso- ciated with SLD in flocks.
Each of the three flocks were transferred to the SLD endemically infected free-range layer site at the usual age of 16 weeks.
Interestingly, at 45 and 75 weeks of age the SLD causal agent c hepaticus was cultured from the bile of healthy cull hens and detected via PCR in the manure of both vaccinated and unvaccinated groups of flockthree.
This trial again was timed so that vaccinated flocks would be at peak of lay during the summer months.
Dead and sick cull hens have characteristic small, white-grey and or red spots on the liver, which can also be swollen with a fibrin covering.
The effect of additives was somewhat hard to analyse, as mortality from SLD was always lower in the cooler months of win- ter.
The trial was planned so that the three flocks would be challenged naturally at the infected layer site, while at peak of lay during the Queensland summer hot weather, when mor- tality and egg production drops historically are the worst.
All management prac- tices were kept exactly the same as usual protocol, besides the hens being vac- cinated.
Ova usually have en- gorged blood vessels, dis- playing hyperaemia – see Figures 1A and 1B.
Vaccinated and unvac- cinated pullets were kept separate in each of the three flocks for life, permitted by the aviary design of the rearing and layer sheds.
This proved that ongoing colonisation and shedding of c hepaticus in the vac- cinated and unvaccinated hens was occurring after their outbreak and for the remainder of flock life.
Results of this trial are ongoing and were present- ed at PIX 2022, during the Egg Session – Spotty Liver.
The financial cost of this disease is significant and can vary from flock to flock.
The above-mentioned fi- nancial cost of the disease – along with the welfare implications, antibiotic use and effect on staff’s general well-being – easily justi- fies the effort required to
Dr Jodi Courtice McLean Farms
Dr Jodi Courtice, egg industry veterinarian.
This is $5000-$42,900 per 10,000 hens.
Each of the three flocks contracted the disease at 30, 26 and 23 weeks of age, with outbreaks going for six or seven weeks.
Across 55 recent SLD outbreaks in peak of lay hens of flocks in Australia, the disease has been cal- culated to cost between
None of these flocks re- quired antibiotic treatment during this trial or later in life.
SLD vaccine costs were not factored into the above financials, however it was found the vaccine paid for itself overall.
Similarly, no flock re- ceived any feed or water additive.
Given the promising re- sults from each of these three flocks on hen wel- fare and financial grounds, a larger scale field trial of 285,000 hens was pro- gressed.
Flocks were managed as per usual farm protocol, however dead hens from each side of the shed were kept separate for post-mor- tem and records, and eggs collected separately for the first 40 weeks of life to
Field vaccine trials stage 2
A total of 285,000 pul- lets of eight aviary rear-
Page 10 – National Poultry Newspaper, October 2022
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