Dr. Isabelle Ruhnke is a Postdoctoral Reserach Fellow at the University of New England, Australia. She graduated in Veterinary Medicine from the
Freie Universität and performed work for her doctoral thesis on glucose transport and gastrointestinal diseases at the Gastrointestinal
Laboratory at Texas A&M University, USA. She worked on the impact of feed technologies and feed particle size on broiler chickens and laying
hens at the Institute of Animal Nutrition, Freie Universität Berlin. Nutrition, health and welfare of chickens became her passion, so Dr.
Ruhnke decided to dedicate her future to the nutritional management of free range laying hens.
Keywords: Laying hens, management, free-range, feeding, predators
In Australia, free-range egg production is a rapidly growing sector with an estimated grocery market value share of 48% of total table egg production. It can be estimated that around 200 commercial free-range egg producers are currently active. This report reflects the current situation these farmers are facing. Adverse climate conditions and Avian Influenza are a concurrent threat to the free-range egg industry. However, on-range feeding is a common feed strategy performed by up to 47.5% of free-range egg producers. With six states and two territories, no national regulations regarding free range hen housing and egg production are in place. In general, two housing systems can be distinguished: fixed housing and mobile housing. The use of guard animals to protect hens from predators is common. The large variety of farming systems and management procedures is reflected in the variety of challenges free-range hens are facing. In a recent survey, free-range layer producers attributed their losses to predation (42%), heat stress (37%), cannibalism (37%), grass impaction (21%), diseases (21%), and malnutrition (5%). Furthermore, internal and external parasites can be considered as widely prevalent. Producers identified that research should be conducted in welfare (52%), pasture management (54%), nutrition (44%), bird health (44%), housing (40%), and economics (29%). With those demands currently under investigation, Australia can be considered as highly active in the field of applied research focusing on free range-egg production.
In Australia, free-range egg production is a rapidly growing sector with an estimated grocery market value share of 48% of total table egg production in 2014, which reflects an increase of 20% compared to 2013 (AECL, 2014). The retail egg value sale of barn laid eggs in 2014 was 9% (increase of 11% compared to 2013), and those of specialty eggs 2% (increase of 18% compared to 2013) (AECL, 2014). With one of the major retailers aiming to phase out cage eggs by 2018, the demand for free-range eggs is expected to continue its upward trend. In 2013, a total of 5,666 registered agricultural businesses produced eggs in Australia (AECL, 2014). The total number of egg producers that housed more than 500 laying hens was 355. Those producers can be considered the key players of the Australian egg industry. Considering that it is not economic to invest on cage infrastructure housing less than 10,000 hens, at least 5,496 farms are free-range egg producers and 186 farms are free-range egg producers with more than 500 hens (key players). Free-range egg production in Australia, whilst rapidly expanding, is also evolving. Establishing free-range egg production enterprises that meet retailer and consumer demands remains a challenge for the poultry industry. In Australia, a total of 14,618 million laying hens are currently registered (AECL, 2014).
Housing of free-range laying hens is orientated towards the Model Code of Practice for the Welfare of Animals (CSIRO, 2002). Referring to this Code, the indoor stocking density for all cage free systems should not exceed 30 kg body weight/m² (15 hens/m²). The floor may consist of litter material or wire/slatted flooring, with gaps between the slats not exceeding 25 cm. According to the Model Code of Practice, the maximum stocking density for the outdoor area is 1,500 hens/hectare (6.6 m²/hen) (CSIRO, 2002). However, any higher stocking density is acceptable when regular rotation of the hens onto fresh range areas is performed and hens are continuously provided with fresh pasture cover. This stocking density is also referred to in the standards from the Royal Society for the Prevention of Cruelty to Animals (RSPCA, 2011). In comparison, individual accreditation bodies, such as the Free Range Egg and Poultry Australia Ltd. (FREPA) implement different standards. The indoor stocking density of FREPA guidelines is determined by the flock size and should not exceed 10 hens/m² when up to 1000 birds/flock are housed, 9 hens/m² when up to 2000 birds are housed, and 8 birds/m² when up to 3000 birds are housed (FREPA, 2015). However, FREPA does not define a stocking density for the outdoor area but refers to the Model Code of Practice and “the range area must be capable of continued production of vegetation”. The Australian Certified Organic Standards regulate indoor stocking density more strictly compared to the Model Code of Practice and FREPA standards, focusing on 16 kg body weight/m² (8 .hens/m²) and a minimum of 18 cm perch space, when at least 1/3rd of the floor is covered with solid floor space and litter material. The stocking density on the range is comparable at 1,500 hens/ha (fixed range) (ACO, 2013) but, when range rotation is performed, stocking density outdoors should not exceed 2,500 birds/ha. While Queensland (QLD) is the only state that has a mandatory regulation of their free-range hen stocking density in place (the stocking density was raised from 1,500 hens/ha range area (6.6 m²/hen) to 10,000 hens/ha (1 m²/hen) in June 2013), no other legally binding regulations are currently in place in any state. Because of the lack of detailed governmental regulations and uniform standards, a broad spectrum of free-range hen management and housing systems can be observed. In particular, the outdoor stocking density is highly debated and a nationwide uniform definition of “free-range” warranted. In June 2015, the elected state peak body representatives (also known as the Egg Farmers Australia) agreed upon a maximum range allowance of 10,000 hens/ha range area to be referred to the fair trade and business regulations, to be included into the draft of the constraint consumer law in 2016. In order to answer the question of the impact of stocking density on hen welfare and behavior, research is being conducted by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of New England. The discussion of a nationwide definition of “free-range” extends beyond the stocking density on the range. The Australian Consumer and Competition Commission oversees the ranging activity of hens housed by major egg producers and decisions of the Federal Court revealed that, in order to declare eggs “free-range”, “laying hens have to move about freely on an open range on most ordinary days” (FCA, 2014).
In order to investigate current farm practices of free-range egg producers all over Australia, an on-line survey and subsequent farm visits were undertaken in 2014 (Singh et al., 2015, Ruhnke et al., 2015a). With a total of 41 egg farmers completing 79 questions regarding their farm, range, feed, rearing, production and health status, as well as the environmental impact and their adaption to the free range system, current challenges and research priorities could be identified. The predominant breed of hens used included Isa Brown (43%), Hy-line Brown (40%), or others such as Lohmann Brown, Bond Brown, Bond White, Bond Black, Plymouth Rock or Australorp (27%) (Singh et al., 2015). While commercial brown laying hens with a European genetic background for intensive in-house cage production are most commonly used, those hens were genetically selected to focus predominantly on productivity and improved feed conversion ratio since being imported. Other characteristics, such as social, feeding, foraging, or ranging behavior did not receive as much attention. Furthermore, current feed recommendations were developed based on housing in a climate controlled environment with limited hen movement. These circumstances may contribute to the fact that average hen body weight /flock obtained on 15 free-range layer farms all over Australia ranged from 1.42 kg-2.1 kg and uniformity of the flock ranged from 83-96% (Singh et al., 2015).
New South Wales (NSW) and the Australian Capital Territory (ACT) have 33% of the national layer flocks, whereas Queensland (QLD), Victoria (VIC), South Australia (SA)/the Northern Territory (NT), Western Australia (WA), and Tasmania (TAS) account for 26%, 25%, 10%, 5%, and 1%, respectively (AECL, 2014). The large geographic distribution of egg producers is reflected by highly diverse climatic challenges. The nationwide survey recently undertaken including 41 free-range layer farmers indicated that heat stress is considered a major cause of mortality (37%) (Ruhnke et al., 2015a). Overall, 45% free-range egg producers reported they do not have any environmental control in their layer housing systems (figure 1). Australian egg producers are generally exposed to extreme weather conditions. According to the results obtained from the free-range survey, 16% of respondents reported experiencing average temperatures of >40⁰C, 19% of respondents reported temperatures of 30-40 ⁰C, and 64 % of farmers frequently experience <0-10°C on the range (Singh et al., 2015). Furthermore, Australian farmers are frequently exposed to extreme droughts, heat waves, and bushfires. The latest flooding was observed in March 2015 in the east coast area of NSW. This flooding resulted in a state-wide decline in egg production. While farmers and hens had to rely on autonomous power sources and helicopter feed delivery for days, significant bird losses including pullets occurred.
A more severe impact on national egg production was experienced in late 2013, when High Pathogenic Avian Influenza (HPAI) was detected in two laying farms in NSW. Most likely introduced by wild birds and then spread by a feed delivery truck, the subsequent culling of hens and secondary effects on the egg market resulted in a nation-wide loss of production of 4%. Low Pathogen Avian Influenza (LPAI) detections and responses were noted frequently with around 80% of the outbreaks happening since 2007. Additionally, there have been four AI incidents requiring national level responses since 2012. While two of those were LPAI detections affecting commercial duck farms, the other two were major HPAI outbreaks in commercial layer farms in November 2012 and October 2013. The fact, that the Avian Influenza was introduced into a free-range layer farm highlights the need for strict biosecurity barriers. All poultry farms have to comply with the “National Farm Biosecurity Technical Manual for Egg production” and should comply with the “Code of Practice for Biosecurity in the Egg Industry” (Grimes and Jackson, 2015; Scott, 2015). Furthermore, the national biosecurity strategy including poultry as one of the 14 sectoral strategies was initiated by Animal Health Australia, a peak industry body that oversees the national system of biosecurity and animal health-related matters. The Avian Influenza generic surveillance procedure is under continuous review and includes detailed information about the monitoring and sampling procedures. Current research into the surveillance of Avian Influenza is conducted by the Rural Industries Research and Development Corporation, the University of Sydney, Charles Sturt University, and several other research institutes.
However, despite the fact that feed and open water sources are important risk factors for the transmission of Avian Influenza, on-range feeding is a common feed strategy performed by up to 47.5% of free-range egg producers (figure 2, Feare, 2010; Ruhnke et al., 2015b). Feed and water on the range frequently attract wild birds and rodents, which are potential vectors for diseases. Recent data suggest the presence of endemic LPAI H5 and H7 in Australian wild birds, which have potential to be introduced to commercial poultry and mutate into HPAI (Grillo, 2015). With 72% of layer farmers reporting that >75% of the flock spend the majority of their time in the outdoors, contact to wild birds can be considered as a major biosecurity risk (Singh, 2015).
Range usage can also frequently be associated with intestinal grass impaction (Ruhnke et al., 2015c). Fresh pasture cover and availability of fodder on the range is a requirement mentioned in most accreditation guidelines (FREPA, 2015; ACO, 2013; CSIRO, 2002). For example, Australian Certified Organic stipulates that the range for organic certified hens shall include edible forage at all times (ACO, 2013). With the recent free-range survey indicating that 43% of free range farmers rotated the range usage, and 53% of free-range farmers used mobile caravan units, 74.4% of all farmers reported that they were able to maintain persistent vegetation and the range area was never stripped bare (figure 3).
While this situation may be beneficial for reducing environmental impact and parasite burden, exposing hens which were genetically selected for intensive in-house cage production to a lush green pasture remains a challenge in many ways. For example, range usage lowered laying performance and increased mortality compared to layers housed in cages (Glatz et al., 2005). The quality and amount of pasture intake may vary significantly among individual birds due to flock behavior and range design (Hegelund et al., 2005; Walker and Gordon, 2003). On some occasions, the curiosity of the hens in combination with the ability of feed selection may result in overconsumption of pasture (figure 4).
In fact, some birds are severely affected in their expected formulated feed intake (Ruhnke et al, 2015c). The nutritional value of pasture is minor. Research has shown that birds given access to pasture may, in part, compensate for small deficiencies in methionine through pasture access (Moritz et al., 2005). However, the predominant polymer of grass is cellulose, which contributes 48% to the total crude fibre fraction (Bach-Knudsen, 1997). Chickens have a very limited ability to access fibre as a nutrient source (Choct et al., 1996; Walker & Gordon, 2003). Depending on the vegetation status of the grass, the non-starch polysaccharide (NSP) content varies between 37-43% and laying hens do not produce endogenous enzymes that can degrade NSPs (Bach-Knutsen, 1997). Constant access to pasture can result in excessive fodder intake, reducing the intake of a balanced feed, leading to undernourishment in energy and essential nutrients such as amino acids (Ruhnke et al., 2015c). Consequently malnutrition occurs, resulting in a severe loss of body condition. In sub-clinical cases, affected birds exhibit reduced performance and in severe cases, death. A recent free-range survey undertaken in Australia indicated that grass impaction is considered to be a mortality concern on up to 21% of farms surveyed (Ruhnke et al., 2015a, Singh et al., 2015). Nutrient requirements of a standard brown laying hen focus on 100-120 g feed intake/hen/day. Those estimations do not take into account extra energy required for free-range birds due to temperature maintenance and additional physical activities. Furthermore, examining crop contents of dead birds that were severely affected by grass impaction led to an estimated grass consumption of up to 60 g grass/day (fresh matter) (Ruhnke et al., 2015c). Others have estimated that the average forage consumption of free-range birds is about 30-40 g dry matter/hen/day, which severely affected the intake of commercially formulated feed, but did not affect productivity (Singh and Cowieson, 2013). In order to minimise the intake of excessive fibre materials such as long grass, range management such as mowing or grazing with cattle or sheep should be considered. Anecdotal evidence provided by farmers suggests that the application of organic acids, such as apple cider vinegar in the drinking water may be of benefit (Ruhnke et al., 2015c). Research investigating several solutions in order to overcome the challenges associated with excessive fibre intake and grass impaction is currently being conducted by the University of Sydney and the University of New England, Australia.
Despite the fact that grass intake can interfere with the consumption of a well-balanced diet, the individual hen faces further nutritional challenges based on individual ranging behaviour. Free-range laying hens spend up to 75% of their day in the outdoors (Keeling et al., 1988). In commercial flocks, the range may be used by 5-95% of the hens (Bubier and Bradshaw, 1998; Hegelund et al., 2005; Hinch and Lee, 2014). A previous study revealed that, when housed in fixed sheds, up to 10% of layers never leave the hen house, while others spend a variable time on the range (Hinch and Lee, 2014). Hence, the freedom of choice results in the development of several sub-populations within one flock. Hens on the range spend not only less time close to their feeders and are less likely to obtain enough formulated feed to satisfy their nutrient requirements; they will also incur higher energy loss due to increased physical activity and maintenance of their body temperature. The urgent need for alternative feeding strategies is reflected by the wide application of highly diverse feeding approaches in practice. Details of results obtained from the free-range survey mentioned earlier regarding the feed source and the feeding strategy are presented in tables 1, 2, and 3 (Ruhnke et al., 2015b, Singh et al., 2015). Additional feed supplements included shell grit (43%), limestone (40%), hay (29%), silage (9%), and others, including vegetables, pasture, insects, and harvested grass (37%) (Ruhnke et al., 2015b, Singh et al., 2015). Hens were fed ad libitum in 78% of cases. The fact that 50% of Australian free-range farmers offer feed on the range and contribute to the risk of the biosecurity status of this industry was already mentioned above. However, current feed recommendations do not always meet the nutrient requirements for the majority of free-range hens. One standard formulation or feeding system ignores not only the different needs of individual hens, but results in an economic waste of feed material. With feed costs contributing more than 50% of the variable costs of free-range egg production, new approaches of feeding management are highly relevant. The current inadequate feeding practice may also contribute to the lower performance and higher mortality seen on free-range farms (Glatz et al., 2005). Investigating nutritional solutions for management of free-range laying hens is a priority of the Poultry Cooperative Research Centre, and the Australian Egg Corporation Ltd, who currently fund research in this area.
Table 1: Feed sources for free-range laying hens (%), n = 40 (Ruhnke et al., 2015b)
Milling facility 62.5
Own production 22.5
Milling facility and own production 5.0
Other (national feed company) 10.0
Table 2: The type of feeding used for Australian free-range laying hens (%), n = 40 (Ruhnke et al., 2015b)
Complete diet 80.0
Choice feeding 7.5
Combined feeding 12.5
Table 3: The structure of feed offered to Australian free-range laying hens, n = 40 (Ruhnke et al., 2015b)
Combined feeding 25.0
Coarse ground 17.5
Fine ground 15.0
The freedom of movement and expression of natural behaviour increase the risk of infection with several parasites, as hens are in contact with excreta allowing intestinal parasites to complete their lifecycle. Consequently the biosecurity in these production systems seems to be fairly poor. However, loose husbandry facilities such as free-range facilities are considered the housing system of the future in Australia and other developed countries. Consequently it is the responsibility of the industry to investigate the impacts, effects and constraints of free-range production systems in order to support the management of these alternative production systems. While mobile sheds are frequently used, rotational ranges are commonly implemented, and low stocking densities with up to 350 hens/ha can be observed, the prevalence for parasite burden may be low. However, the last investigation about the prevalence of intestinal parasites in the Australian poultry was conducted in 1942 (Broadbent, 1942). When questioning free-range egg producers in Australia about their parasite monitoring and control, 58.6% of farmers noticed external and/or internal parasites in their flock (Singh et al., 2015). However, subsequent investigations revealed that many farmers never or rarely checked for parasite infestation. The survey also revealed that 20% of farmers are unsatisfied or completely unsatisfied with the options available for preventing and treating parasites. Survey responses also revealed that some of the parasite control information available to free-range producers is speculative, subjective and incomplete. Excreta sampling on farms provided evidence that Ascaris galli may be the most prevalent parasitic infection in the Australian free-range egg industry, which is in general agreement with findings in free-range enterprises in other countries (Jansson et al., 2010; Kaufmann, 2011; Sherwin et al., 2013; Yazwinski et al., 2013). Parasitic infections in livestock are costly, due to expenses for medical treatment, secondary infections and other direct or indirect losses caused by reduced performance and/or death of the hen. The direct impact of parasites such as Ascaris galli on the economy of the Australian egg production remains unknown. While the total eradication of parasites in a free-range environment is unfeasible, the threshold to which level such parasites can be accepted has not been determined to date. Since only efficient monitoring of the parasite load enables farmers and farm managers to control the parasite infections, there is a need for developing accurate and practical test measurements. Research in this area is currently performed by CSIRO in collaboration with the University of New England. The applied approach aims to provide free range producers with tools that will allow for effective parasite monitoring, aimed at increased compliance and reducing the likelihood of therapeutic drug resistance. Chemicals, anthelmintics and pesticides are registered in Australia for the control of internal or external parasites in birds. Currently, only levamisole is registered for use to control nematode parasite in commercial layer flocks in Australia. Other medication such as piperazine is registered for some other classes of poultry such as young birds and breeder flocks. Drug resistance of anthelmintics is widespread in many regions of the world. In Australia, resistance will likely evolve against the only registered layer product (levamisole) if its use is widespread and poorly controlled. Currently, there is no scientific data available about the prevalence or parasites and the use of anthelmintics, as well as the drug resistance.
Free range laying farmers attributed their losses to a wide variety of causes (table 4) (Ruhnke et al., 2015a). Maremma dogs and Alpacas are frequently placed with the flock in order to protect the hens from predators (figure 5). Usually, a couple of guard animals are introduced to the flock early on, and accompany them for the rest of their life. When asked why they have switched to free-range egg production, the following reasons were given: bird welfare reasons (64%), consumer demand (60%) and to produce a better quality product (53%) (Singh et al., 2015: Ruhnke et al., 2015a). The focus on hen welfare is reflected in concern about feather pecking and cannibalism and the wide variety of hen treatment in respect to beak trimming. Plumage scoring obtained on 15 free-range farms revealed that the majority of birds are affected by severe feather pecking and/or cannibalism (Singh et al., 2015). This observation supports research conducted in 2008, where cannibalism and vent pecking were major causes of mortality in all Australian states (Nagle et al., 2008).
Table 4: Causes for mortality in free-range egg enterprises (%), n = 30 (Ruhnke et al., 2015a). Multiple reasons for death could be named by farmers.
Heat stress 37.0
Grass impaction 21.0
Based on information from the recent free-range survey, 50% of the free range farms did not beak-trim their hens (Singh et al., 2015). Both the Model Code of Practice and the FREPA standards support minimal beak trimming by competent persons qualified under the national competency standards (CSIRO, 2011; FREPA, 2015). Therefore, the practice of infrared trimming at day one and additional hot blade trimming later in life is common in Australian laying hens and it is not expected to be regulated in the near future. An increased activity of animal welfare groups is expected but their impact on regulations is unknown. However, organisations such as the Australian Certified Organic do not allow for beak-trimming, nor do they permit routine vaccination (ACO, 2013). Therefore, research of practical innovations to reduce the occurrence of aggression, severe feather pecking, and cannibalism in free-range laying hens is warranted. Currently, scientific evidence to establish best practice in free-range systems, including the use of pecking stones, range cover, and stocking density that may optimise welfare conditions is under investigation.
Free-range egg production pushed by the supermarkets is reshaping the Australian egg industry. While the country is characterised by its deregulated industry standards, a broad variety of housing systems and management actions exist. Some of the key characteristics include family operated farms, the use of mobile sheds and farming focus on a low environmental impact by maintenance of pasture cover on the range. A nation-wide survey identified key characteristics, current challenges and research priorities, such as biosecurity, malnutrition, parasitism, severe feather pecking and cannibalism. Applied research is highly warranted and currently conducted by intensive collaboration of various research organisations and interdisciplinary research teams. Improving the health and welfare of free-range laying hens, reflected by optimised egg production, is of highest priority to the Australian egg industry.
The author thank the Australian Egg Corporation Limited for providing statistical information on farm demographics, and Bede Burke, Chair of The NSW Farmers Association as well as Mingan Choct, CEO of the Poultry Cooperative Research Centre for constructive feedback. Many of the statistics quoted come from project 2.9.2. funded by the Poultry CRC, established and supported under the Australian Government’s Cooperative Research Centres Program.
AECL (2014) Custom data base, Australian Egg Corporation Limited, Sydney.
ACO, Australian Certified Organic (2013) Australian Certified Organic Standard – the requirements for organic certification, Australian Organic Ltd, Nundah, Queensland, Australia
Bach-Knudsen, K. E. (1997) Carbohydrate and lignin contents of plant materials used in animal feeding. Anim. Feed Sci. Technol. 67: 319-338.
Broadbent, M. (1942) Survey of the incidence, distribution and prevalence of the helminth parasites of the domestic fowl in Queensland. Aust. Vet. J. 18: 200-204.
Bubier, N. E. (1998) Movement of flocks of laying hens in and out of the hen house in four free range systems. Br. Poult. Sci. 39: 5-6.
Choct, M., Hughes, R. J., Wang, J., Bedford, M. R., Morgan, A. J., & Annison, G. (1996) Increased small intestinal fermentation is partly responsible for the anti‐nutritive activity of non‐starch polysaccharides in chickens. Br. Poult. Sci. 37: 609-621.
CSIRO publishing (2002) Primary Industries Standing Committee, Model Code of Practice for the Welfare of Animals, Domestic Poultry, 4th Edition, Collingwood, Victoria, Australia
FCA (2014), Federal Court of Australia, http://www.judgments.fedcourt.gov.au/judgments/Judgments/fca/single/2014/2014fca1028
Feare C. J. (2010) Role of wild birds in the spread of highly pathogenic Avian influenza Virus H5N1 and implications for global surveillance. Avian Diseases. 54: 201-212.
FREPA (2015) Free Range Egg Standards, Free Range Egg and Poultry Australia Ltd., Benalla, Victoria. http://www.frepa.com.au/standards/egg-standards/
Glatz, P. C., Y. J. Ru, Z. H. Miao, S. K. Wyatt and B. J. Rodda (2005) Integrating poultry into a crop and pasture farming system. Int. J. Poult. Sci. 4: 187-191.
Grillo, T. (2015) Contribution to the 2012 Avian Influenza in Wild Birds Surveillance Program. RIRDC Publication No 15/016 RIRDC Project No PRJ-008337 (https://rirdc.infoservices.com.au/items/15-016)
Grimes, T. and C. Jackson (2015) Code of practice for biosecurity in the egg industry, Australian Egg Corporation Limited. https://www.aecl.org/assets/www.aecl.org/outputs/AECL-Biosecurity-Code-of-Practice-2nd-Ed-January-2015.pdf
Hegelund, L., J. T. Sørensen, J. B. Kjær and I. S Kristensen (2005) Use of the range area in organic egg production systems: effect of climatic factors, flock size, age and artificial cover. Br. Poult. Sci., 46: 1-8.
Hinch G. and C. Lee, C (2014) New approaches to assess welfare in free range laying hens. Poultry CRC – Final Report Project No 1.5.2.
Jansson, D.S., A. Nyman, I. Vagsholm, D. Christensson, M. Goransson, O. Fossum, and J. Höglund (2010) Ascarid infections in laying hens kept in different housing systems. Avian Pathol. 39: 525-532.
Kaufmann, F. (2011). Helminth infections in laying hens kept in alternative production systems in Germany-Prevalence, worm burden and genetic resistance, Doctoral dissertation, Niedersächsische Staats-und Universitätsbibliothek Göttingen
Keeling, L. J., B. O. Hughes and P. Dun (1988) Performance of free-range laying hens in a polythene house and their behavior on range. Farm Building Progress, 94: 21-28.
Leeson, S. and J. D. Summers (2009) Commercial poultry nutrition 3rd ed. Nottingham University Press, Nottingham, UK.
Moritz, J. S., A. S. Parsons, N. P. Buchanan, N. J. Baker, J. Jaczynski, O. J. Gekara and W. B. Bryan (2005) Synthetic methionine and feed restriction effects on performance and meat quality of organically reared broiler chickens. J. Appl. Poult. Res. 14: 521-535.
Nagle, T. A. and P. C. Glatz (2012) Free range hens use the range more when the outdoor environment is enriched. Asian-Austral. J. Anim. Sci. 25: 584-591.
RSPCA (2011) RSPCA Approved Farming scheme standards Layer Hens. http://www.rspca.org.au/sites/default/files/website/what-we-do/working-with-farming-industry/RSPCALayerhensStandards.pdf
Ruhnke I, C. DeKoning, K. Drake, P. Glatz, T. Walker T, A. Skerman, P. Hunt, M. Sommerlad, M. Choct and M. Singh (2015a) Free range farm demographics and practices in Australia. Proc APSS, 26: 260.
Ruhnke I., C. DeKoning, K. Drake, M. Choct and M. Singh (2015b) Feeding Practices in Australian Free-Range Egg Production. – unpublished data, abstract accepted for the European Symposium of Poultry Nutrition, 2015.
Ruhnke I., G. Cowling, M. Sommerlad, R. Swick and M. Choct (2015c) Gut impaction in free-range hens. Proc. APSS 26: 242-244.
Scott, P. (2015) National Farm Biosecurity Technical Manual for Egg Production, Animal Heath Australia and Egg Corporation Limited http://www.farmbiosecurity.com.au/wp-content/uploads/2015/04/National-Farm-Biosecurity-Technical-Manual-for-Egg-Production.pdf
Sherwin, C. M., M. A. F. Nasr, E. Gale, M. Petek, K. Stafford, M. Turp and G. C. Coles (2013) Prevalence of nematode infection and faecal egg counts in free-range laying hens: relations to housing and husbandry. Br. Poult. Sci. 54: 12-23.
Singh. M., I. Ruhnke, C. DeKoning, K. Drake, P. Glatz, T. Walker T, A. Skerman, P. Hunt, M. Sommerlad and M. Choct (2015) Free range poultry survey 2014 – farm demographics and practices. Poultry CRC report –unpublished data
Singh, M. and A. J. Cowieson (2013) Range use and pasture consumption in free-range poultry production. Anim. Prod. Sci. 53: 1202-1208.
Walker, A. and S. Gordon (2003) Intake of nutrients from pasture by poultry. Proc. Nutr. Soc., 62: 253-256.
Yazwinski, T., C. Tucker, E. Wray, L. Jones, Z. Johnson, S. Steinlage and J. Bridges (2013) A survey on the incidence and magnitude of intestinal helminthiasis in broiler breeders originating from the southeastern United States. J Appl. Poult. Res. 22: 942–947.
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