Australian Broiler Research Articles

Dominant Salmonella Serovars in Australian Broiler Breeder Flocks and Hatcheries: a Longitudinal Study.

A longitudinal study was conducted to determine the dominance and prevalence of Salmonella enterica subsp in Australian broiler breeder flocks and hatcheries. Twenty-two flocks (n = 3339 samples) were sampled over 6 time points beginning at placement until week 40. Hatcheries (n = 274 samples) were sampled following removal of chicks hatched from eggs originating from the 22 donor parent flocks. The percent of positive flocks (36%) and frequency of positive samples (15.6%) were highest during rearing at week 7. The frequency of positive samples decreased over the 40 weeks; however, the number of positive flocks remained relatively consistent. Geographical location had a greater influence on Salmonella detection frequency than company sample origin, despite differing management and vaccination protocols within and between companies. Twelve serovars were detected in total. The predominant serovars during rearing were Salmonella Mbandaka (32%), S. Saintpaul (27%), and S. Liverpool (18%). The predominant serovars detected during production were S. Cubana (27%), S. Saintpaul (24%), and S. Havana (13%). Salmonella Typhimurium, S. Ohio, and S. Hessarek were detected in the hatcheries. Of the serovars detected, only S. Typhimurium and S. Ohio were found in both broiler breeder flocks and hatcheries. However, detection did not correspond to the status of the flock eggs feeding into the hatchery. This study provides an up-to-date capture of the current Salmonella serovars circulating in the broiler breeder industry. Continued surveillance within the Australian Chicken Meat industry is imperative to mitigate and reduce the risk of salmonellosis in the community related to chicken meat. IMPORTANCE This study identified prevalent and dominant Salmonella enterica subsp in Australian Broiler Breeder flocks, as well as in hatcheries post chick hatch and removal, from eggs originating from these donor parent flocks. The captured Salmonella data was further compared to the most common Salmonella serovars isolated from broilers, as well as human salmonellosis notification data, which is useful for consideration of the circulating serovars within the chicken meat industry and their significance in public health. As there are multiple entry points for Salmonella during the entire chicken meat production chain that can lead to carcass contamination, it is important to distinguish serovars present between the different stages of vertical integration to implement and enable Salmonella control strategies.

Salmonella enterica subsp. salamae serovar Sofia, a prevalent serovar in Australian broiler chickens, is also capable of transient colonisation in layers

ABSTRACT1. Salmonella enterica subsp. salamae serovar sofia (S. sofia) is a prevalent strain of Salmonella in Australian broilers and has been isolated from broiler chickens, litter, dust, as well as pre- and post-processing carcasses, and retail chicken portions but has never been reported in commercial Australian layers or eggs.2. To investigate whether a S. sofia isolate from a broiler could colonise layers, one-month-old Hyline brown layers were orally inoculated with S. sofia and colonisation was monitored for 2–4 weeks.3. Overall, 30–40% of the chickens shed S. sofia from the cloaca between 6 and 14 d post-inoculation which then declined to 10% by d 21. Necropsy at 2 weeks post-inoculation revealed 80% of birds harboured S. sofia in the caecum, whilst, by 4 weeks post-infection, no chickens were colonised with S. sofia in the gastrointestinal tract, liver or spleen. Additionally, no aerosol ‘bird to bird’ transfer was evident.4. This study demonstrated that laying hens can be colonised by broiler-derived S. sofia; however, this colonisation was transient, reaching a peak at 14 d post-inoculation, and was completely cleared by 28 d post-inoculation. The transience of colonisation of S. sofia in layers could be a factor explaining why S. sofia has never been detected when screening for Salmonella serotypes found in Australian laying hens or eggs.

Assessing the probability of introduction and spread of avian influenza (AI) virus in commercial Australian poultry operations using an expert opinion elicitation.

The objective of this study was to elicit experts’ opinions and gather estimates on the perceived probability of introduction and spread of avian influenza (AI) virus in the Australian broiler and layer industry. Using a modified Delphi method and a 4-step elicitation process, 11 experts were asked to give initial individual estimates for the various pathways and practices in the presented scenarios using a questionnaire. Following this, a workshop was conducted to present group averages of estimates and discussion was facilitated to obtain final individual estimates. For each question, estimates for all experts were combined using a discrete distribution, with weights allocated representing the level of expertise. Indirect contact with wild birds either via a contaminated water source or fomites was considered the most likely pathway of introduction of low pathogenic avian influenza (LPAI) on poultry farms. Presence of a water body near the poultry farm was considered a potential pathway for introduction only when the operation type was free range and the water body was within 500m distance from the shed. The probability that LPAI will mutate to highly pathogenic avian influenza (HPAI) was considered to be higher in layer farms. Shared personnel, equipment and aerosol dispersion were the most likely pathways of shed to shed spread of the virus. For LPAI and HPAI spread from farm to farm, shared pick-up trucks for broiler and shared egg trays and egg pallets for layer farms were considered the most likely pathways. Findings from this study provide an insight on most influential practices on the introduction and spread of AI virus among commercial poultry farms in Australia, as elicited from opinions of experts. These findings will be used to support parameterization of a modelling study assessing the risk of AI introduction and spread among commercial poultry farms in Australia.

Quantitative effects of in-line operations on Campylobacter and Escherichia coli through two Australian broiler processing plants

Campylobacter is an important food borne pathogen, mainly associated with poultry. A lack of through-chain quantitative Campylobacter data has been highlighted within quantitative risk assessments. The aim of this study was to quantitatively and qualitatively measure Campylobacter and Escherichia coli concentration on chicken carcasses through poultry slaughter. Chickens (n=240) were sampled from each of four flocks along the processing chain, before scald, after scald, before chill, after chill, after packaging and from individual caeca. The overall prevalence of Campylobacter after packaging was 83% with a median concentration of 0.8log10CFU/mL. The processing points of scalding and chilling had significant mean reductions of both Campylobacter (1.8 and 2.9log10CFU/carcase) and E. coli (1.3 and 2.5log10CFU/carcase). The concentration of E. coli and Campylobacter was significantly correlated throughout processing indicating that E. coli may be a useful indicator organism for reductions in Campylobacter concentration. The carriage of species varied between flocks, with two flocks dominated by Campylobacter coli and two flocks dominated by Campylobacter jejuni. Current processing practices can lead to significant reductions in the concentration of Campylobacter on carcasses. Further understanding of the variable effect of processing on Campylobacter and the survival of specific genotypes may enable more targeted interventions to reduce the concentration of this poultry associated pathogen.

Application of high‐resolution melting curve analysis for typing of fowl adenoviruses in field cases of inclusion body hepatitis

Fowl adenoviruses (FAdVs) cause inclusion body hepatitis (IBH) in chickens. In this study, clinical cases of IBH from Australian broiler flocks were screened for the presence and genotype of FAdVs. Twenty-six IBH cases from commercial poultry farms were screened. Polymerase chain reaction (PCR) coupled with high-resolution melt (HRM) curve analysis (PCR/HRM genotyping) was used to determine the presence and genotype of FAdVs. For comparison, field isolates were also assessed by virus microneutralisation and nucleotide sequence analysis of the hexon loop 1 (Hex L1) gene. PCR detection of chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) was also employed. FAdV-8b and FAdV-11 were identified in 13 cases each. In one case, FAdV-1 was also identified. Cross-neutralisation was observed between the FAdV-11 field strain and the reference FAdV-2 and 11 antisera, a result also seen with the type 2 and 11 reference FAdVs. Field strains 1 and 8b were neutralised only by their respective type antisera. The FAdV-8b field strain was identical to the Australian FAdV vaccine strain (type 8b) in the Hex L1 region. The Hex L1 sequence of the FAdV-11 field strain had the highest identity to FAdV-11 (93.2%) and FAdV-2 (92.7%) reference strains. In the five cases tested for CAV and IBDV, neither virus was detected. The evidence suggested the presence of sufficient antibodies against CAV and IBD in the parent flocks and there was no indication of immunosuppression caused by these viruses. These results indicate that PCR/HRM genotyping is a reliable diagnostic method for FAdV identification and is more rapid than virus neutralisation and direct sequence analysis. Furthermore, they suggest that IBH in Australian broiler flocks is a primary disease resulting from two alternative FAdV strains from different species.

Metabolic Mechanisms Only Partially Explain Resistance to Pyrethroids in Australian Broiler House Populations of Lesser Mealworm (Coleoptera: Tenebrionidae)

The susceptibility of six Australian broiler house populations and an insecticide susceptible population of lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), to cyfluthrin, beta-cyfluthrin, gamma-cyhalothrin, and deltamethrin was investigated. One broiler house population had equivalent susceptibility to the susceptible to beta-cyfluthrin and beta-cyhalothrin, with higher susceptibility to cyfluthrin and deltamethrin. The remaining five populations demonstrated strong resistance to cyfluthrin (19-37-fold), the insecticide used most widely for management of A. diaperinus in Australia. Each cyfluthrin-resistant population demonstrated reduced susceptibility to beta-cyfluthrin (resistance ratios were 8-17-fold), deltamethrin (2.5-8-fold), and gamma-cyhalothrin (6-12-fold) compared with the laboratory population, but cross-resistance patterns varied considerably between populations. Adding piperonyl butoxide (PBO) had no effect on the susceptibility of the susceptible population to any of the insecticides, but it increased the susceptibility of each of the five cyfluthrin-resistant populations: to cyfluthrin (synergism ratio range, 1.9-5.0-fold), beta-cyfluthrin (1.6-4.1-fold), and y-cyhalothrin (1.7-2.0-fold). PBO had a more variable effect on susceptibility to deltamethrin, with three of the cyfluthrin-resistant populations being more susceptible to deltamethrin in the presence of PBO, but susceptibility of the remaining two populations was unaffected by adding PBO (synergism ratio range, 0.9-2.5-fold). Overall, the addition of PBO to the four pyrethroids had variable effects on their susceptibility. This variability indicated the presence of other resistance mechanisms in beetle populations apart from metabolic resistance. In addition, the relative importance of metabolic resistance in each beetle population varied widely between pyrethroids. Thus, it cannot be assumed that PBO will reliably synergize pyrethroids against cyfluthrin-resistant lesser mealworm populations when using it to mitigate insecticide resistance.

Responses of Susceptible and Cyfluthrin-Resistant Broiler House Populations of Lesser Mealworm (Coleoptera: Tenebrionidae) to γ-Cyhalothrin

Gamma-Cyhalothrin was proposed as an agent for management of lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), in Australian broiler houses. From 2007 to 2009, baseline susceptibility of 20 Australian broiler farm beetle populations plus an insecticide-susceptible laboratory population was determined for gamma-cyhalothrin by using topical application. In addition, repeat testing and regression analyses of specific beetle populations to gamma-cyhalothrin showed that topical application was a very reliable and repeatable testing method. The 21 populations were tested with a cyfluthrin discriminating concentration (based on LC(99.9), 0.0007% [AI]) to identify possible cross-resistance. Across all populations, there was a significant linear relationship between the gamma-cyhalothrin LC50 value and mortality induced by the cyfluthrin LC(99.9). Full cyfluthrin baseline studies of seven populations indicated that gamma-cyhalothrin was twice as toxic as cyfluthrin, even against susceptible beetles and resistance ratios at the cyfluthrin LC50 and LC(99.9), varied considerably, with maxima of 56.6 and 83.6 respectively. Corresponding ratios for gamma-cyhalothrin for the same populations were 8.6 (LC50) and 7.9 (LC(99.9)). There were no significant correlations between beetle weights and gamma-cyhalothrin LC50 or LC(99.9), values. A discriminating concentration of 0.005% (AI) gamma-cyhalothrin was chosen to detect any future changes in susceptibility. Results of this study suggest that cyfluthrin can confer cross-resistance to gamma-cyhalothrin in A. diaperinus, but the magnitude of this resistance is unpredictable. Thus, widespread and frequent cyfluthrin use in broiler houses in eastern Australia, which has selected for cyfluthrin resistance, also has resulted in reduced susceptibility to gamma-cyhalothrin. Due to its higher relative toxicity, gamma-cyhalothrin is still potentially useful for management of lesser mealworm, but due to cross-resistance issues, adoption of gamma-cyhalothrin for broiler house use will require a cautious and judicious approach.

Quantifying Transmission of Campylobacter jejuni in Commercial Broiler Flocks

Since meat from poultry colonized with Campylobacter spp. is a major cause of bacterial gastroenteritis, human exposure should be reduced by, among other things, prevention of colonization of broiler flocks. To obtain more insight into possible sources of introduction of Campylobacter into broiler flocks, it is essential to estimate the moment that the first bird in a flock is colonized. If the rate of transmission within a flock were known, such an estimate could be determined from the change in the prevalence of colonized birds in a flock over time. The aim of this study was to determine the rate of transmission of Campylobacter using field data gathered for 5 years for Australian broiler flocks. We used unique sampling data for 42 Campylobacter jejuni-colonized flocks and estimated the transmission rate, which is defined as the number of secondary infections caused by one colonized bird per day. The estimate was 2.37 +/- 0.295 infections per infectious bird per day, which implies that in our study population colonized flocks consisting of 20,000 broilers would have an increase in within-flock prevalence to 95% within 4.4 to 7.2 days after colonization of the first broiler. Using Bayesian analysis, the moment of colonization of the first bird in a flock was estimated to be from 21 days of age onward in all flocks in the study. This study provides an important quantitative estimate of the rate of transmission of Campylobacter in broiler flocks, which could be helpful in future studies on the epidemiology of Campylobacter in the field.

Baseline Responses of <I>Alphitobius diaperinus</I> (Coleoptera: Tenebrionidae) to Spinosad, and Susceptibility of Broiler Populations in Eastern and Southern Australia

Spinosad was proposed as a potential chemical for control of lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), in Australian broiler houses after the detection of strong cyfluthrin resistance in many beetle populations. In 2004-2006, spinosad susceptibility of 13 beetle populations from eastern and southern Australian broiler houses and a cyfluthrin/fenitrothion-resistant reference population was determined using topical application, and was compared with the susceptibility of an insecticide-susceptible reference population. Comparisons of dose-response curves and baseline data showed that all populations, including the insecticide-susceptible population, were roughly equivalent in their response to spinosad, indicating no preexisting spinosad resistance. Two field populations, including the resistant reference population, which had confirmed cyfluthrin/fenitrothion-resistance, showed no cross-resistance to spinosad. There was no significant correlation between beetle weight and LC9.9. A discriminating concentration of 3% spinosad was set to separate resistant and susceptible individuals. Considering the levels of spinosad resistance that have been recorded in other insect pests, the sustained future usefulness of spinosad as a broiler house treatment will rely on effective integrated beetle management programs combined with carefully planned chemical use strategies.

Recent advances in Australian broiler litter utilisation

The global poultry industry is undergoing many changes, one being the need for efficient disposal of its broiler litter (BL) due to a reduction in the land available for cost effective disposal. To date, Australian BL disposal has been achieved by selling the litter as a fertiliser to agricultural sectors. Research indicates BL and other poultry industry waste streams could be used as a food source for vermiculture systems, allowing the sale of vermi-cast as a biologically enhanced fertiliser and worms for protein. If this approach is economically viable then the poultry industry could reduce its environmental impact and operate more like a closed loop system. Integrated bio-systems using vermiculture, composting and waste-to-energy technologies have developed significantly overseas and have shown potential to solve many of the issues associated with poultry waste disposal.

The application of a polymerase chain reaction (PCR)-based capillary electrophoretic technique provides detailed insights into Eimeria populations in intensive poultry establishments

Intestinal coccidiosis, caused by one or multiple species of Eimeria (Protozoa: Apicomplexa), is one of the most important infectious diseases affecting chickens. In this study, we used a polymerase chain reaction (PCR)-based capillary electrophoresis (CE) approach to conduct an epidemiological survey of Eimeria species in seven Australian broiler flocks, varying in age from 18 to 42 days. We confirmed that all seven recognized Eimeria species of poultry were present. Eimeria acervulina and E. maxima were the most common, followed by E. mitis (i.e., 89%, 87% and 64% of chickens, respectively). E. praecox was present in 44% of birds, whereas E. brunetti and E. tenella were uncommon, being found in 36% and 26%, respectively. E. necatrix was rarely detected (10%). Even the least common species were present in more than 70% of sheds. The prevalence of individual species was higher in older than in younger chickens. Most of the chickens sampled were simultaneously infected with multiple Eimeria species (mean=3.6). The number of Eimeria oocysts excreted per gram of faeces reached a peak at 36 days of age, before declining to a considerably lower level by 42 days. As anticoccidial drugs were permanently withdrawn at 36 days, the decreasing Eimeria oocyst excretion rates indicated the development of protective immunity in the chickens. The present study showed that even healthy chickens usually harbour numerous species of Eimeria. The CE technique proved to be a time and cost-effective means of investigating the epidemiology of Eimeria in commercial establishments.

Baseline Responses of Adult <I>Alphitobius diaperinus</I> (Coleoptera: Tenebrionidae) to Fenitrothion and Susceptibility Status of Populations in Queensland and New South Wales, Australia

Traditionally in Australia, regular applications of insecticide to the floors and lower walls of broiler houses after cleanout periods have been used in an attempt to control lesser mealworm, Alphitobius diaperinus (Panzer). The Australian chicken meat industry has been concerned in recent years with the failure to control A. diaperinus in its broiler houses by using this method and with large beetle populations breaching farm biosecurity. Resistance to fenitrothion was suspected to be responsible for these recent control failures. In response, beetles from 13 poultry facilities were compared with an insecticide-susceptible reference population by using a topical application method. Generally, strong resistance to fenitrothion (up to 79 times that of the susceptible at the LC50) occurred in populations of A. diaperinus in long-established broiler growing areas of southeastern Queensland, where fenitrothion had been used continuously for up to 20 yr. In newly established broiler growing areas, where considerably less fenitrothion had been used (i.e., approximately 5 yr), much weaker or no resistance occurred. In addition, dose-mortality data generated for the susceptible reference beetle population over a range of fenitrothion concentrations showed that 0.15% fenitrothion at a LC(99.9) level could be used as a convenient topical dose concentration to discriminate between susceptible and resistant individuals. Using this method, the susceptibility of 27 field populations of A. diaperinus was determined. Of this total, 23 populations did not exhibit complete mortality against the discriminating concentration (mortality range 0-98.7%). Application of fenitrothion in Australian broiler houses for control of A. diaperinus has now ceased.

Single and concurrent avian leukosis virus infections with avian leukosis virus-J and avian leukosis virus-A in Australian meat-type chickens

Australian broiler breeders were screened for avian leukosis viruses (ALVs) (May 2001 to December 2003) as surveillance of measures to reduce the prevalence of ALV-J. Samples of blood (4233), albumen (1122), meconium (99) and tumours (16) were obtained from 93 flocks in six Australian states. Virus isolation was performed in C/O chick embryo fibroblast cultures, which were initially screened by group-specific antigen enzyme-linked immunosorbent assay, with follow-up confirmation using polymerase chain reaction. The chronology of isolations reveals the circulation of both ALV-J and ALV-A during this period. On 16 occasions single isolations were found to contain both ALV-A and ALV-J. This is the first report of dual infections with two subgroups of ALV occurring in the same chicken. The effectiveness of ALV-J eradication measures is indicated by the absence of any ALV-J isolations in late 2003. ALV-A however, continued to be isolated from the broiler population. The detection of dual infections, as well as the ongoing occurrence of ALV-A in meat-type birds, is discussed in the context of ongoing potential for recombinations and the associated threat for the emergence of avian leukosis virus with changes in host range and pathogenicity.

Detection of subgroup J avian leukosis virus infection in Australian meat‐type chickens

To determine the extent of avian leukosis virus subgroup J (ALV-J) infection in Australian broiler breeder flocks, using virus isolation and molecular biological detection. Any resultant ALV-J viral isolates to be characterised by neutralisation cross testing in order to determine antigenic relationships to overseas isolates of ALV-J. Samples of blood, feather pulp, albumen and tumours were obtained from broiler breeder flocks which represented four genetic strains of meat chickens being grown in Victoria, South Australia, NSW and Queensland. Dead and ailing birds were necropsied on farm and samples were collected for microscopic and virological examinations. Virus isolation was carried out in C/O and DF-1 CEF cultures and ALV group specific antigen was detected in culture lysates using AC-ELISA. Micro-neutralisation assay was used for antigenic characterisation of selected isolates. Genomic DNA was isolated from cultured cells, tumours and feather pulp. ALV-J envelope sequences were amplified by PCR using specific ALV-J primers while antibodies against ALV-J were detected by ELISA. A total of 62 ALV-J isolates were recovered and confirmed by PCR from 15 (31.3%) of 48 breeder flocks tested. Antibody to ALV-J was detected in 20 (47.6%) of the 42 flocks tested. Characteristic lesions of myeloid leukosis caused by ALV-J were found in affected flocks. The gross pathological lesions were characterised by skeletal myelocytomas located on the inner sternum and ribs, neoplastic enlargement of the liver, and in some cases gross tumour involvement of the spleen, kidney, trachea, skeletal muscles, bone marrow, skin and gonads. Microscopically, the tumours consisted of immature granulated myelocytes, and were present as focal or diffuse infiltrations in the affected organs. Virus micro-neutralisation assays demonstrated antigenic variation among Australian isolates and to overseas strains of ALV-J. ALV-J infection was prevalent in Australian broiler breeder flocks during 2001 to 2003. Australian isolates of ALV-J show a degree of antigenic variation when compared to overseas isolates.

Lentogenic Newcastle disease virus and respiratory disease in Australian broiler chickens.

Lentogenic Newcastle disease virus and respiratory disease in Australian broiler chickens.

The effect of dietary lysine and methionine concentrations on the growth characteristics and breast meat yields of Australian broiler chickens

Two experiments were conducted with an Australian broiler strain to determine the optimum dietary lysine and methionine concentrations for growth and breast meat yield. In the first experiment, supplementing lysine to 14.1 and 13.0 g/kg in combination with methionine supplemented to 6.2 and 5.3 g/kg in starter and finisher diets respectively, resulted in significant improvements in breast meat yield with no effect on growth rate. Increasing the crude protein concentration by increasing the concentrations of all indispensable amino acids to balance the additional lysine and methionine supplements improved weight gain but gave no further improvement in breast meat yield. In the second experiment, dietary concentrations of 13.1 and 12.5 g lysine/kg and 6.5 and 5.1 g methionine/kg in starter and finisher diets respectively, were found to support optimum liveweight gain when supplemented individually. A further study was conducted to confirm that the ranges in age and bodyweight at which breast meat yield was measured had no significant effect on breast meat yield. The optimum dietary concentrations of lysine and methionine observed in these studies are higher than those recommended by the Standing Committee on Agriculture (1987) for broilers in Australia.

Serum Total Calcium, Phosphorus, 1,25-Dihydroxycholecalciferol, and Endochondral Ossification Defects in Commercial Broiler Chickens

The research described in this paper relates the changes in serum concentration of calcium, phosphorus, and 1,25-dihydroxycholecalciferol [l,25(OH)2 D3] to changes in tibial ash percentage and the incidence of endochondral ossification defects (EOD) in flocks of commercially reared broiler chickens at 14 d of age.Sequential studies of six Australian broiler flocks representing three major genetic lines were undertaken at weekly intervals from 1 to 28 d of age. Serum collected from birds was analyzed for total calcium, inorganic phosphorus, and l,25(OH)2 D3. Tibial ash percentage was also determined at weekly intervals, and the incidence of EOD was determined at 14 d of age by examining sagittal sections of the proximal tibiotarsus.The EOD observed in the 14-d-old broiler chickens were characterized by enlarged zones of proliferating chondrocytes, similar to that which occurs during calcium- or vitamin D-dependent rickets. Three flocks had a 50% incidence of EOD at 14 d of age and were classified as severely affected. The other three flocks had incidences ranging from 12 to 16% and were classified as mildly affected.Broiler flocks severely affected with EOD (50% incidence at Day 14) had lower (P ≤ .05) concentrations of l,25(OH)2 D3 than flocks mildly affected (12 to 16% incidence). Tibial ash percentages were lower (P ≤ .05) in the severely affected flocks between Days 14 to 28, and it is likely that a lower rate of ash accretion between Days 7 to 14 precedes the development of the EOD.From these studies it is evident that flocks with a high incidence of EOD have significantly lower bone ash and 1,25 (OH)2 D3 compared with mildly affected flocks, and it seems probable that higher systemic concentrations of l,25(OH)2 D3 between 7 to 14 d of age will enhance the ability of broiler chickens to effectively mineralize the cartilaginous growth plates in the appendicular skeleton during early bone maturation.

Responses of different strains of Australian broiler chickens to feed restriction at an early age

Male chickens from the three most common commercial broiler strains in Australia were fed conventionally or on a regimen which restricted growth by approximately 58% between 6 and 12 days of age followed by ad libitum feeding. Early age feed restriction had no significant effect on bodyweight at 47 days of age, and feed was utilized significantly more efficiently with all three strains. Restriction significantly reduced abdominal fat and had no significant effect on the yield of breast meat. The large improvements in feed efficiency and reductions in abdominal fat have major implications with regard to the economics of broiler meat production.

Sex and strain responses to aflatoxin B1in the chicken

A series of experiments was conducted to investigate the effects of both continuous and single dose ingestion of aflatoxin B1 on Australian broiler chickens. Aflatoxin levels above 0.5 mg/kg diet decreased food intake and food conversion and retarded growth. The severity of the response and the ability of the birds to recover was dose related and dependent on the strain and sex of the chicken, males being more susceptible. Relative liver weight and liver lipid concentration were increased and significant changes occurred in liver fatty acid composition at this dietary level of aflatoxin B1. Mortality from a single dose of aflatoxin B1 occurred within 72 hours with an approximate LD50 of 15-18 mg aflatoxin B1/kg body-weight for the more susceptible male chickens.

The inheritance of tibial dyschondroplasia in broilers.

A breeding programme to develop a line of chickens with a high incidence of tibial dyschondroplasia (TD) from Australian broiler stock is described. Despite the absence of a control flock, this programme has demonstrated that selection in a broiler population can rapidly increase the incidence of TD. There was consistent circumstantial evidence of the presence of a major sex-linked gene, the recessive allele of which is associated with an increased incidence of TD. The realised heritability estimates (obtained in the absence of a control flock) consistently exceeded 1.00, suggesting the presence of an environmental trend favourable to the onset of TD over the four generations of this investigation. There was a high maternal component or dominance genetic component, or both, for the inheritance of TD in the final generation, suggesting that environmental factors associated with the female parent line may influence the incidence of TD in broilers.