Association of feed efficiency with organ characteristics and fatty liver haemorrhagic syndrome in laying hens

Poor feed efficiency (FE) in hens impacts body weight (BW) and may reflect suboptimal health. Fatty Liver Haemorrhagic Syndrome (FLHS) is mostly observed in laying hens and affects egg production and hen performance. The aim of this study was to investigate the relationships of FE and BW with organ characteristics, liver composition and incidence of FLHS of 150 individually housed ISA Brown hens ranked on the basis of feed conversion ratio (FCR) attained from early lay. At 45 weeks, 10 birds per FE group (HFE-High feed efficient; MFE-medium feed efficient; LFE-low feed efficient) were randomly selected and euthanized. Hen BW was positively associated with feed intake and FCR. The HFE hens had a lower abdominal fat pad and liver weight compared to LFE hens. FLHS lesion score was higher (worse) in the LFE than HFE hen group and was moderately positively associated with BW and abdominal fat pad, but strongly positively associated with liver weight. Liver pathology of LFE hens showed hepatocytes with abnormal retention of lipids causing distended cytoplasmic vacuoles compared to the HFE hens. Hens which exhibited poorer FE in early lay had heavier abdominal fat pads, heavier, fatter livers and were more prone to FLHS.

The role of hen body weight and diet nutrient density in an extended laying cycle

The egg production (EP), egg quality and health of heavier or lighter hens fed a diet of either higher nutrient density (HND) or lower nutrient density (LND) during early lay, was assessed at very late lay. Based on their body weight (BW) at 18 wk of age (WOA) ISA Brown pullets were allocated as either heavier weight (HW; average 1.65 kg) or lighter weight (LW: average 1.49 kg). Half of each BW group received the HND (2,901 kcal/kg; 17.6% crude protein (CP) or LND (2726 kcal/kg, 16.4% CP) diet from 18 to 24 WOA. From 25 to 90 WOA all birds received identical early, then mid and late-lay diets. Hen BW was measured after peak-lay (36 WOA) and at 90 WOA. At 89 WOA and across 18 to 36 and 18 to 89 WOA feed intake (FI), EP, egg mass (EM), and feed conversion ratio (FCR) were calculated. Eggshell quality, breast score, relative ovary weight and liver and bone health were evaluated in very late lay. Differences in BW continued to 90 WOA. At 36 WOA HW hens produced heavier eggs, and had higher 18 to 36 WOA cumulative FI, EM (P < 0.001) and FCR (P < 0.05). When 89 WOA HW birds consumed more feed (P < 0.001) but EP, EM and FCR did not differ from LW hens. Cumulatively, 18 to 89 WOA FI and EM were higher for HW hens (P < 0.05), but cumulative EP and FCR was not different. The early-lay HND diet improved very late lay eggshell thickness (P < 0.05) and shell breaking strength (P = 0.05). Lighter hens fed HND and HW hens fed LND diet produced heavier eggs, higher relative oviduct weight and lower liver lipid peroxidase in very late lay (P < 0.05). Bone strength did not differ, but LW hens had higher femoral manganese and zinc (P < 0.05), lowering their likelihood of osteoporosis. Overall LW hens sustained EP throughout a longer laying cycle with beneficial bone characteristics. The HND diet improved eggshell strength and, in LW hens reduced hepatic oxidation.

The influence of hen size and diet nutrient density in early lay on hen performance, egg quality and hen health in late lay

The effect of hen size and diet nutrient density during early lay on egg production (EP) at 24 and 69 wk of age (WOA) and late lay egg quality and hen health was evaluated. Based on bodyweight (BW) at 18 WOA ISA Brown hens were assigned as heavier (HW; n = 120) or lighter weight (LW; n =120). Sixty birds from each BW group were fed an early-lay diet of higher nutrient density (HND), or lower nutrient density (LND) between 18 and 24 WOA. From 25 WOA all hens received the same early-lay diet and then from 40 WOA the mid-lay diet. Hen average daily feed intake (ADFI), hen-day EP, egg weight (EW), egg mass (EM), and feed conversion ratio (FCR) were assessed at 24 and 69 WOA. Between 66 and 70 WOA eggshell and internal egg quality was evaluated and at 70 WOA BW, liver and bone health were assessed. At 24 WOA BW was highest in HW birds and birds receiving the HND diet (P < 0.01). Concurrently ADFI, and FCR were higher and hen-day EP was lower in HW compared to LW birds (P < 0.05). The HND diet resulted in lower ADFI and FCR at 24 WOA, but higher EW and EM compared to the LND diet (P < 0.01). At 69 WOA HW birds had higher ADFI, EW (P < 0.02) and heavier 70 WOA BW compared to LW hens. The lower FCR of the LW birds at 69 WOA was approaching significance (P = 0.054). Hen weight and diet density did not affect 69 WOA egg production. Between 18 and 69 WOA cumulative FI and EM were higher in HW hens (P < 0.01) than LW hens, as was cumulative FCR (P = 0.053). Hen weight and diet density did not alter 66–70 WOA internal egg quality, but the HND diet generated thicker eggshells and higher eggshell breaking strength (P < 0.05). Seventy WOA liver health, keel curvature and femur breaking strength did not differ. Overall LW hens had lower FCR than HW hens and the early-lay HND diet facilitated improved eggshell integrity during late lay compared to the LND diet.

An evaluation of bird weight and diet nutrient density during early lay on ISA brown performance, egg quality, bone characteristics and liver health

This study compared the impact of a higher nutrient density (HND) or lower nutrient density (LND) diet fed during early lay to either heavier weight (HW) or lighter weight (LW) ISA Brown hens. At 18 wk of age (WOA) pullets (n = 240) were evenly assigned to either HW (n = 120) or LW (n = 120). Sixty birds from each weight group were then randomized to either the HND or LND diet treatments which were fed from 18 to 24 WOA inclusive. At 25 WOA the LND diet replaced the HND diet. All hens remained on LND diet to 50 WOA. Hen performance was measured from 18 to 50 WOA. Femur and liver health were evaluated at 50 WOA. Egg quality was assessed from 46 to 50 WOA. The 18 WOA HW hens had higher BW, cumulative egg production, cumulative feed intake (CFI), and cumulative egg mass (CEM) to both 24 and 50 WOA (P < 0.01). At 24 WOA the HND diet also generated higher BW (P < 0.001), CEM (P < 0.001) and lower cumulative feed conversion ratio (CFCR) (P < 0.01), the latter being sustained to 50 WOA (P < 0.01). At 50 WOA CFCR of LW birds was lower than HW birds (P < 0.01). Egg weight (EW), yolk diameter, and percent yolk weight were higher (P < 0.05) in the HW birds with the highest albumen to yolk ratio in LW birds (P < 0.05). Egg shape index was higher in LND diet fed birds (P < 0.01) while LW hens had higher shell phosphorus (P < 0.05). Body weight and diet nutrient density interacted on femoral diameter and cortical thickness being higher (P < 0.01) in LW birds fed HND than LW birds fed LND diets. Fatty liver hemorrhagic scores (P < 0.05) and liver lipid peroxidase (P < 0.001) at 50 WOA were higher in HW and LND diet treatments. Concurrently HW birds had the highest CFI and EW while CFCR and liver health were superior in LW and the HND diet treatment.

Comparison of performance and carcass composition of a novel slow-growing crossbred broiler with fast-growing broiler for chicken meat in Australia

Slow-growing broilers offer differentiation in the chicken meat market for consumers who have distinct preferences based on perceived higher welfare indices and willingness to pay a higher price for the product. Although breeding for slow-growing broilers is relatively advanced in Europe and the United States, it is limited in Australia. Crossbreeding is one of the approaches taken to developing slow-growing broiler strains. Thus, the aim of this study was to compare performance, immune response, leg health, carcass characteristics, and meat quality of a novel crossbred slow-growing broiler breed (SGB) with the conventional, fast-growing Cobb 500 broiler (CB) to assess their suitability as an alternative for chicken meat production in Australia. A total of 236 one-day-old broiler chicks (116 SGB and 120 fast-growing CB) were reared on standard commercial diet in an intensive production system. Birds and feed were weighed on a weekly basis and feed intake and feed conversion ratio calculated. At 21 d of age, a 2% suspension of sheep red blood cells was injected subcutaneously into 8 broilers of each breed to compare their antibody response. Birds from both breeds were grown to a final live weight of 2.0–2.2 kg, before a latency-to-lie (LTL) test, carcass analysis and apparent metabolizable energy (AME) assay were performed. The SGB reached the target weight at 55 d of age compared with 32 d in CB. However, SGB stood for longer during LTL, had higher thigh, drumstick, and wing yields (as a percentage of carcass weight) as well as darker and redder meat in comparison with the CB. The CB had better feed conversion efficiency, higher antibody (IgM) production, higher AME, heavier breast yield, and lower meat drip loss than the SGB. Although fast-growing CB outperformed the SGB for traditional performance parameters, the crossbred in this study was comparable with other slow-growing broiler breeds and strains across different countries and is thus a suitable candidate for a slow-growing alternative in Australia.

Changes to Cobb 500 chick characteristics, bone ash, and residual yolk mineral reserves during time spent in the hatcher

Previous work has identified an effect of hatch time on chick femur mineralization. This experiment assessed the impact of hatch time and a 24-h post-hatch unfed time period on chick bone mineralization and yolk mineral utilization. In early hatching chicks, yolk Mg, Zn, K, P, Fe, and Cu decreased by 40 to 50% over the 24-h post-hatch unfed time period, whereas yolk Ca and Na decreased by 25 to 40% (P = 0.026). Yolk Sr was intermediate, decreasing by 37%. Late hatching chicks which had been hatched for no more than 30 h had a higher femur bone ash percentage compared to early hatching chicks which had spent over a 30-hour sojourn unfed in the incubator (P = 0.013). These results indicate that removing chicks from the incubator within 30 h of their hatch is likely to benefit their femoral mineralization.

Changes to mineral levels in the yolk of meat chicken embryos during incubation

A total of 864 settable Cobb 500 eggs were used to explore changes in yolk mineral content during incubation. Eggs were individually weighed and then placed in a commercial incubator. On embryonic day (ED) 0, 6.5, 13.5, and 17.5, 36 eggs were sampled and yolk weight and mineral content were determined. The concentration of iron (Fe), phosphorus (P), and zinc (Zn) declined (P < 0.05) from ED0 to ED17.5. The concentration of calcium (Ca), magnesium (Mg), and strontium (Sr) increased (P < 0.05) from ED0 to ED17.5. The concentration of copper (Cu), potassium (K), and sodium (Na) increased initially (ED0 to ED6.5) but declined thereafter. There was no change (P > 0.05) in the concentration of yolk manganese (Mn) from ED0 to ED17.5. Substantial changes in yolk mineral concentration occur during incubation and are presumably associated with mobilization of shell reserves and flux between albumen and yolk. These data may be useful in designing in ovo interventions, optimizing meat chicken breeder premix formulation or assembly of suitable neonatal or pre-starter diets for meat chicken chicks.

Why did severe feather pecking and cannibalism outbreaks occur? An unintended case study while investigating the effects of forage and stress on pullets during rearing

This 2 × 2 factorial experiment aimed to investigate the effects of stimulating foraging behavior from wk 6 and imposed stress at wk 16 on the development of severe feather pecking (SFP) in chickens reared for free-range egg production. Non-beak-trimmed ISA Brown chicks were purchased at one day old and floor-reared on wood shavings. From wk 6, straw was provided daily in dispensers (Forage vs. No forage) to stimulate foraging. At wk 15, there were 16 pens of 50 pullets. "Stressors" were applied to half the pens in wk 16 via combined transport, relocation, and mixing (TRM) of pullets, simulating activities around transfer from the rearing to egg-laying farm (TRM vs. Not TRM). Range access was permitted from wk 21. Behavior, plumage damage (PD), growth, egg production, feed use, injuries, and mortalities were recorded, along with litter moisture and pH. In wk 26, an SFP outbreak commenced. By wk 34, PD was worse in south- than north-aspect pens (P < 0.001). Further, PD was more affected by side of the shed than the experimental treatments. In wk 30, an outbreak of injurious pecking (IP) commenced in the 4 TRM-treatment pens on the south side, with IP deaths almost 3 times more common in the Forage+TRM than No forage+TRM treatment. We suggest factors associated with a 13-day rainfall event that occurred in late winter predisposed the flock to SFP. While multiple factors such as winter cold, muddy ranges, damp floor litter with elevated pH, among others coincided, hens were clearly more impacted in south- than north-aspect pens. Once initiated, SFP possibly spread via social learning, and by wk 40, ∼98% of hens had PD. Interestingly, the IP outbreak was related to a combination of factors (stressors?), such as being housed in colder, damper south-aspect pens (note: southern hemisphere), having added Forage, and TRM. These unexpected relationships could help direct future research to identify the specific factors involved in the causation of SFP and IP/cannibalism outbreaks.

Spotty Liver Disease: A review of an ongoing challenge in commercial free-range egg production

Spotty Liver Disease is an acute infectious disease of layer chickens that was likely first described in the USA and Canada in the 1950s and 1960's. The disease occurs almost exclusively in barn and free-range production systems. Outbreaks usually, but not exclusively occur in young layers (≅25 weeks) at peak of lay. Indicators of SLD include an acute drop in egg production of up to 35%, together with increased mortality of up to 15%. A presumptive diagnosis at post mortem is made with the detection of characteristic small yellow-white necrotic hepatic lesions, together with a fibrinous peri-hepatitis, excess pericardial and peritoneal fluid, and usually enteritis with diarrhoea. Histopathology reveals a multifocal acute hepatocellular necrosis with fibrin and occasional haemorrhage. Control measures trialled include use of antibiotics, improved biosecurity and hygiene, as well as management practices directed at reducing stress in flocks. However, none other than treatment with antibiotics has been consistently effective which suggested a bacterial aetiology. In 2015, a novel fastidious thermophilic, microaerobic campylobacter was isolated from symptomatic SLD flocks in the UK. Subsequently, an Australian group isolated and further characterised a genetically similar bacterium and named it Campylobacter hepaticus. The bacterium can be cultured from the liver and bile of infected birds, although recovery from non-sterile organs such as the caecum and duodenum remains elusive. Consequently, the route of transmission remains unconfirmed, although molecular detection by PCR of C. hepaticus DNA in the gastrointestinal tract and faeces of SLD infected birds is highly suggestive of a faecal-oral route.

Live and inactivated vaccine regimens against caecal Salmonella Typhimurium colonisation in laying hens

Objective

In Australia, Salmonella serovar Typhimurium (S. Typhimurium) is the predominant zoonotic serovar in humans and is frequently isolated from layer hens. Vaccination against this serovar has been previously shown to be effective in broilers and the aim of this current study was to assess and determine the best vaccination strategy (live or inactivated) to minimise caecal colonisation by S. Typhimurium.

Methods

A long‐term experiment (56 weeks) was conducted on ISABROWN pullets using a commercial live aroA deleted mutant S. Typhimurium vaccine and an autogenous inactivated multivalent Salmonella vaccine (containing serovars Typhimurium, Infantis, Montevideo and Zanzibar). These vaccines were administered PO or by SC or IM injection, either alone or in combination. Pullets were vaccinated throughout rearing (to 18 weeks of age) and sequentially bled for antibody titre levels. The birds, vaccinated and controls, were challenged orally with a field isolate of S. Typhimurium at different ages, held for 21 days post‐challenge, then euthanased and their caeca cultured for the presence of Salmonella.

Results

None of the oral live‐vaccinated groups exhibited lasting protection. When administered twice, the inactivated vaccine gave significant protection at 17 weeks of age and the live vaccine given by SC injection given twice produced significant protection at 17, 25 and 34 weeks.

Conclusions

Vaccination regimens that included parenteral administration of live or inactivated vaccines and thus achieved positive serum antibody levels were able to provide protection against challenge. Hence, vaccination may play a useful role in a management strategy for Salmonella carriage in layer flocks.

Pathotyping of Australian isolates of Marek's disease virus in commercial broiler chickens vaccinated with herpesvirus of turkeys (HVT) or bivalent (HVT/SB1) vaccine and association with viral load in the spleen and feather dander

OBJECTIVE

To pathotype Australian isolates of Marek's disease virus (MDV) in commercial broiler chickens using standard methods and to evaluate early markers of pathotype.

METHODS

A complete 3 × 4 factorial experiment with two replicates was conducted using 648 Cobb broiler chickens in 24 isolators. The experimental factors were vaccination (unvaccinated, herpesvirus of turkeys (HVT), bivalent (HVT + SB1 strain of serotype 2 MDV)) and MDV challenge (unchallenged or 500 plaque-forming units of isolates MFP57, 02LAR or FT158). Mortality, body weight, immune-organ weights and viral load were measured to 56 days post challenge (dpc). Vaccinal protective index (PI) and virulence rank (VR) were calculated based on gross Marek's disease (MD) pathology.

RESULTS

The PIs provided by the HVT and bivalent vaccines against challenge with MPF57, 02LAR, and FT158 were 84.6% 56%, 61.4% and 82.2%, 60.8%, 57.7%, respectively, leading to putative pathotypes of virulent MDV for MPF57 and very virulent MDV for 02LAR and FT158. Significantly more of the unvaccinated chickens (85.7%) had MD lesions than chickens vaccinated with either the HVT (26.8%) or bivalent vaccine (27.6%). Strong linear relationships were observed between the incidence of MD at 56 dpc and MDV load in the spleen at 7 dpc (R(2) = 0.71) and MDV load in the isolator exhaust dust at 14 dpc (R(2) = 0.57) and 21 dpc (R(2) = 0.51). Immune organ weights had a weaker association with subsequent MD incidence.

CONCLUSION

Pathotyping results in broiler chickens with maternal antibody broadly agreed with those in specific-pathogen-free chickens in other studies, with some important differences. MDV load in the spleen at 7 dpc and in isolator dust at both 14 and 21 dpc was a powerful early predictor of subsequent MD incidence.

Development of a chick bioassay for determination of infectivity of viral pathogens in poultry litter

OBJECTIVE

To develop a chicken bioassay to detect infective viral pathogens in poultry litter and to determine the effects of type of chicken and age of exposure, as well as the effect of simulated litter transportation, on the level of viral infectivity detected.

DESIGN

A 5 × 2 × 2 factorial design, plus negative controls. Five chicken litters, including two with deliberate contamination (one transported and one not), two chicken types (specific-pathogen-free (SPF) Leghorns and Cobb broilers) and two ages at initial exposure (days 1 and 8). Two replicates of each treatment combination.

METHODS

The 10 chickens in each of 22 isolators were either exposed (20 isolators) or not (2 isolators) to 8 L of previously used or deliberately contaminated poultry litter in two deep scratch trays. At day 35 post-exposure, sera were assayed for antibodies against chicken anaemia virus (CAV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), Newcastle disease virus (NDV) and fowl adenovirus (FAV). Spleen samples were tested for Marek's disease virus (MDV) using real-time polymerase chain reaction.

RESULTS

The bioassay detected CAV, IBDV and FAV, but not NDV, IBV or MDV, in chickens exposed to infected litters. Infection in SPF chickens was detected with greater sensitivity than in the broiler chickens. Sensitivity increased with age at exposure in broiler but not SPF chickens. Simulated transportation for 24 h had little effect on pathogen detection.

CONCLUSION

A bioassay based on the exposure of day-old SPF chickens to poultry litter and measurement of seroconversion at day 35 post-exposure is a useful semi-quantitative assay for viral infectivity in poultry litter, with overnight transportation of litter having little effect on the level of viral infectivity detected. This bioassay has applications in research on litter treatment protocols.

Influence of vaccine deposition site on post-vaccinal viraemia and vaccine efficacy in broiler chickens following in ovo vaccination against Marek's disease

In ovo vaccination against Marek's disease is a widely used technology in the broiler industry.A series of experiments was carried out to determine the site of vaccine deposition in the egg during automated in ovo vaccination, and the effect of vaccine deposition site and dose on vaccine responses following vaccination with cell-associated herpesvirus of turkeys in commercial broiler chickens. Vaccine deposition site following automated in ovo vaccination was principally influenced by the age of embryo, with egg size having a smaller effect. The frequency of vaccine deposition inside the embryo body increased as incubation progressed from day 17.5 to 19.5. In experiments using manual vaccine deposition intra-embryonically (IE) or extra-embryonically (EE) at day 18.5, EE vaccine deposition resulted in a significantly delayed development of post-vaccinal viraemia relative to both IE vaccination and subcutaneous vaccination at hatch. There were no effects of vaccine dose (2000, 4000 or 8000 plaque forming units) on the timing of post-vaccinal viraemia. The timing of post-vaccinal viraemia was found to be a good indicator of the level of protection provided by the vaccine against challenge with earlier viraemia associated with better protection. IE vaccine deposition induced significantly greater protection than EE deposition against challenge with a virulent strain of Marek's disease virus. IE deposition consistently produced a high level of protection (68 to 84%) irrespective of vaccine dose or challenge day, while EE vaccine deposition produced no or low levels of protection (0 to 27%) depending on the vaccine dose and day of challenge. The growth of challenged chickens was also affected by site of vaccine deposition, with significantly higher live weights at day 56 of age in IE compared with EE vaccinated groups. These data suggest that the site of vaccine deposition within the embryo is an important determinant of the success of in ovo vaccination.

A validated miniaturized MPN method, based on ISO 6579:2002, for the enumeration of Salmonella from poultry matrices

AIMS

To validate the effectiveness of a miniaturized most probable number method (mMPN) in enumerating Salmonella from poultry matrices.

METHODS AND RESULTS

A MPN was developed, based on the ISO 6579:2002 method using modified semi-solid Rappaport-Vassiliadis media as the sole selective medium. The validation of the mMPN was shown to not differ significantly from, at the 95% confidence level (Student's t-test P = 0·357) to, the traditional 9-tube MPN (tMPN) using pure cultures of Salmonella ser. Typhimurium, Infantis, Montevideo, Muenster and Salmonella subsp II 1,4,12,27:b:[e,n,x] (Sofia). The validation of naturally and artificially contaminated poultry matrices (carcasses, scald tank water, faeces, caeca and feed) showed that detection using the mMPN compared well to the ISO 6572:2002; sensitivity (92%), specificity (97%) and agreement (KAPPA 0·72). The quantitative comparison between the tMPN and mMPN methods showed that 92% of enumerations were less than ± 1 log different (Student's t-test = 0·13). Financial analysis showed that the mMPN required 64% less media and 56% less labour than the tMPN.

CONCLUSION

The mMPN is a consistent, easy to automate method for the enumeration of Salmonella from different poultry matrices.

SIGNIFICANCE AND IMPACT OF STUDY

The miniaturized MPN reduces the material and labour cost of the method and enables the uniform and accurate measurement of the effectiveness of intervention strategies in the control of Salmonella colonization of poultry.

Effects of vaccine dose, virus challenge dose and interval from vaccination to challenge on protection of broiler chickens against Marek's disease virus challenge

OBJECTIVES

To examine the effects of varying the doses of turkey herpesvirus (HVT) vaccine and Marek's disease virus (MDV) challenge at two intervals after vaccination on the protection of chickens against challenge with MDV.

DESIGN AND PROCEDURE

Experiment 1, a dose response study, consisted of 11 doses of HVT vaccine administered at hatch followed by challenge with 100 plaque forming units (pfu) of MDV 5 days post vaccination. Experiment 2, a 2 x 6 x 2 factorial design, included two HVT vaccine types, six different doses of HVT vaccine and 50 pfu and 200 pfu of MDV challenge 2 days post vaccination. All chickens were reared up to day 56 post challenge when all survivors were killed humanely. Dead and killed chickens were examined for gross MD tumours.

RESULTS

Experiment 1 showed a significant positive linear relationship between dose of HVT vaccine and protective index in chickens challenged 5 days post vaccination. However the range of protective index observed was limited. In Experiment 2 neither HVT vaccine provided significant protection at any dose. There was no significant effect of vaccine type or MDV challenge dose on overall protection against challenge. Chickens challenged with 200 pfu of MDV had significantly higher mortality and MD incidence than those with 50 pfu.

CONCLUSIONS

HVT vaccine dose had a significant impact on protective index, but vaccination to challenge interval appeared to have greater impact on the protective efficacy of vaccination. A fourfold increase in challenge dose increased mortality rate and incidence of MD.

Synthesis of triclinic calcium pyrophosphate crystals

This paper presents a method for preparing crystals of triclinic calcium pyrophosphate (t-CPPD). A calcium pyrophosphate intermediate is first prepared by reaction of potassium pyrophosphate and calcium chloride. Samples of the intermediate are dissolved in hydrochloric acid and urea added. Upon heating to 95-100 degrees C, hydrolysis of the urea causes the pH to rise and t-CPPD crystallises out. Purity of the product was ascertained by chemical and physical analysis. Where large crystals are required an unstirred system is used, while smaller crystals are produced by stirring the reaction mixture.

Immunosuppressive effects of Marek's disease virus (MDV) and herpesvirus of turkeys (HVT) in broiler chickens and the protective effect of HVT vaccination against MDV challenge

Much of the impact of Marek's disease in broiler chickens is considered to be due to immunosuppression induced by Marek's disease virus (MDV). The present study evaluates the effects of an Australian isolate of pathogenic MDV (strain MPF 57) and a non-pathogenic vaccinal strain of herpesvirus of turkeys (HVT) (strain FC 126) on the immune system of commercial broiler chickens for 35 days following challenge at days 0 or 3 of age. It also investigates the extent of protection provided by HVT vaccine against MDV-induced immunosuppression. Immune system variables, including relative lymphoid organ weight, blood lymphocyte phenotype (CD45+/CD3+, putatively T, and CD45+/LC+, putatively B) and antibody production following vaccination against infectious bronchitis (IB) at hatch, were used to assess the immune status of chickens. Immunosuppression was also assessed by susceptibility to secondary challenge with pathogenic Escherichia coli on day 29 post-MDV challenge. MDV infection reduced the weight of the thymus and bursa of Fabricius, the numbers of circulating T lymphocytes and B lymphocytes, and IB antibody titre. The timing of these effects varied. MDV infection greatly increased susceptibility to E. coli infection. HVT alone caused mild depletion of T and B lymphocytes but no effect on immune organ weight or IB titre. Vaccination with HVT provided good protection against most of the immunosuppressive effects of MDV but not against MDV-induced growth impairment and reduced responsiveness to IB vaccination, suggesting that recent Australian strains of MDV may be evolving in virulence to overcome the protective effects of HVT.

Antibody responses to avian encephalomyelitis virus vaccines when administered by different routes

Antibody responses to a commercial avian encephalomyelitis virus (AEV) vaccine administered by different routes were measured by an enzyme-linked immunosorbent assay (ELISA). Responses to single doses of vaccine administered by the ocular route to 10% of a flock were comparable with those obtained when all birds received a single dose in the drinking water. However, ocular vaccination of 5% of the flock resulted in significantly lower responses than those obtained when 10% were vaccinated. Maternal antibody was shown by the ELISA to persist in chickens from vaccinated flocks for up to 21 days after hatching. Day-old chickens with serum absorbances of < 0.3 at 492 nm, as determined by the ELISA, were shown to be susceptible to intracerebral challenge with the neurotropic Van Roekel strain of AEV.