Scientific studies and reviews I found interesting. I've composed this list mainly for myself, but seeing as it can interest others, I'll post it publicly. Word of warning; I'm not educated, only interested in knowing as much about my hobby as possible. Will forever be updated...
Language rated as X/10. Where 1 is normal conversation and 10 is "is this even English???".
I only post open articles, and mostly reviews as they're more informative and easier to read. If it's too boring, I recommend reading the introduction and conclusion (discussion).
The where to and how to's
There's a significant amount of research available online.
Poultry Science is the online library from the journal paper with the same name. Many of the articles are free to read.
ScienceDirect holds a lot of different journals, but most articles must be bought to read anything more than the abstract.
PubMed Central is a better alternative for finding open articles.
Researchgate offers an enormous amount of science papers of every kind. If you find a paper somewhere else that you don't have access to, try searching for the entire title here.
Google Scholar searches only renown scientific sites. Very useful tool!
Other sources: Canadian Science Publishing, MDPI (all articles open access), Poultry Hub list over scientific journals, International Journal of Poultry Science.
How to read scientific papers: Reviews are essentially an article with many citations to different studies. They're easy to read in full and offer a big perspective on a subject. List of studies will be found at the bottom of the article, with links if available. I use the word review here on any article that's not a study. Studies are harder to read. Unless you're particularly interested in scientific methods, the easiest is to read the introduction and jump to results and discussion (summary). Check both the results and the scientists interpretation of the results.
Most research on chickens are done on layer hens and broilers. Mostly this can translate in one way or another onto backyard chickens.
Word of warning: some scientific studies involves killing embryos or animals to examine them. Others involve exposing animals to stress.
Sophisticated Fowl: The Complete Behavior and Cognitive Skills of Chickens and Red Junglefowl
Review. 3/10. Recommended
Summary: "We have here reviewed the sensory abilities, social and sexual behaviour, personality, affective state, and cognition of fowl, including, where relevant, some of the implications of these topics for their welfare."
Thinking chickens: a review of cognition, emotion, and behavior in the domestic chicken
Review. 5/10. Biological language.
Summary: "In this paper, I have identified a wide range of scientifically documented examples of complex cognitive, emotional, communicative, and social behavior in domestic chickens which should be the focus of further study."
A review of environmental enrichment for laying hens during rearing in relation to their behavioral and physiological development
Review. 5/10. Biological language.
Summary: On the importance of early enrichment. I've use this heavily in my article about enrichment for chicks.
Influences of Maternal Care on Chicken Welfare
Review. 3/10. Recommended
Summary: On broodies, chicks and their relationship. "We discuss the important features of maternal care in chickens, the behavioural consequences of deprivation, and the welfare implications on commercial farms."
More Than Eggs - Relationship Between Productivity and Learning in Laying Hens
Study. 3/10. Added 25. June.
Summary: Contrary to the study's hypothesis, hens from a high-production line performed better in food-rewarded learning tests than moderate-production. This shows that, even though behavior is changed through the breeding race towards top productivity of hens, their intelligence is not diminished. One factor considered was that the high-production hens were more motivated by food due to their higher need for nutrition.
The Chicken Challenge: What Contemporary Studies of Fowl Mean for Science and Ethics
Review. 4/10. PDF. Added 25. June.
Summary: Chickens (especially roosters) communicate to each other by specific signals. Not only is this understood by the other flock members, but each individual reason and react according to what they perceive as the severity of the situation. Chickens learn by watching other flock members, particularly the dominant ones. Article also discusses brain size and development, and the implications of housing cognitive complex creatures in high density conditions.
Relatedness and age reduces aggressive male interactions over mating in domestic fowl.
Study. 3/10. Added 25. June.
Summary: "We demonstrate that both old and young dominant males interrupt a lower proportion of related subordinate male copulation attempts than those of unrelated subordinates, suggesting that male fowl show kin tolerance during male–male competition over mating. Older males show an overall reduced level of copulation interruptions than younger males."
About domestication and genetics
Domestication-related genetic effects on behavior in chickens - effects on genotype at a major growth quantitative trait locus
Study. 5/10. Genetics.
Summary: As supported by other studies, this study which involves both pure breed red jungle fowl, domesticated chickens and crosses between the two finds that domestication reduces fear response and aggression in chickens, particularly males.
Breeding of tomorrow's chicken to improve well-being
Review. 5/10. Recommended - genetics
Summary: About domestication and artificial selection in breeding chicken generally. Particularly about altering strains of layer hens by selecting genetic traits responsible for behavior such as fearfulness and aggressiveness.
Observations on the reproductive behaviour of domestic fowl in the wild and Feeding behaviour in a population of domestic fowls on the wild
3 part study. 4/10. Added 29. June
Summary: The infamous experiment of D.G.M. Wood-Gush and Ian Duncan where they put domesticated chickens on an uninhabited Scottish island to fend for themselves. The chickens were predated by mink, but still managed to survive and reproduce 3 (?) years. Their diet consisted of grass, oats that were planted for them, seeds, broad leaves, roots and insects. The chicks ate mostly insects the first month of their lives. Most hens went broody several times a year, and hatched chicks. They never revisited a nesting site, and were good at hiding them. The first study; "Some behavioural observations on domestic fowl in the wild" is not open access unfortunately. It's cited heavily in other articles, especially the roosting behavior observed.
Continuous study of breeding wild Red Junglefowl towards domestication
Added 28. June. I'm putting this in its own section, since it encompasses many studies. A scientist named Per Jensen started in 2010 to breed wild Red Junglefowl located in Sweden. This is sort of the poultry-version of the famous russian silver fox domestication-experiment.
They started with undomesticated junglefowl and bred two lines; high fear and low fear. in two generations, based on where the birds ended in a fear-towards-humans test. After 8 generations, the L-strain show lower stress, higher metabolism, they're larger and lay larger eggs, are more socially dominant and their brains have started to look different.
Study 1: Heritability and Genetic Correlation of Fear-Related Behavior in Red Junglefowl - Possible Implications on Early Domestication
Study 2: Red Junglefowl (Gallus Gallus) selected for low fear of humans are larger, more dominant and produce larger offspring
Study 3: Is domestication driven by reduced fear of humans? Boldness, metabolism and serotonin levels in divergently selected red junglefowl
Study 4: Domestication and tameness: brain gene expression in red junglefowl selected for less fear of humans suggests effects on reproduction and immunology
Study 5: Brain size is reduced by selection for tameness in Red Junglefowl - correlated effects on vital organs
Study 6: Activite, social and sexual behavior in Red Junglefowl selected for divergent levels of fear towards humans
"There were a number of behavioural differences between the selection lines indicating that tameness may affect traits not advertently selected for. Overall, the results show that selection for tameness only, mimicking the early phase of chicken domestication, has affected a range of other behaviours as correlated responses."
Investigating the Global Dispersal of Chickens in Prehistory Using Ancient Mitochondrial DNA Signatures
Study. 5/10. Genetics.
Summary: It's been theorized that the domestication of red junglefowl happened several times during history. This study found 3 distinctively different genetic markers in ancient chicken bones. Marker 1 was shown both in Remote Oceania, America and Europe. Marker 2 was only found in Thailand. A third marker was found in Micronesia and in one sample from South America, suggesting a Pre-Columbian transfer of chickens from Remote Oceania to Peru.
Mixed ancestry and admixture in Kauai's feral chickens: invasion of domestic genes into ancient Red Junglefowl reservoirs
Study. 5/10 Added 01. July
Summary: The remote island of Kauai holds a unique population of feral chickens, decendant of the Red Junglefowl the people first inhabiting the island brought with them. In later times, both other Red Junglefowl has been introduced, as well as escaped domestic chickens. They found genetic markers both belonging to birds both from Asia and Europe. These birds are a unique hybrid between junglefowl and domestic chicken.
Factors affecting Intestinal Health in Poultry
Review. 6/10. Recommended
Summary: The chicken's gastrointestinal tract is the barrier between feed ingested and the bird. It's an important part of the immune system and contains a diverse microflora to break down feed. The earlier the GI tract starts to process food, the healthier and bigger the chicks become.
Parasites, bacterial infections, viruses and toxins can heavily affect the intestinal health. Spesific view on necrotic enteritis and coccidiosis
Review: Anti-nutritional effects of phytic acid in diets for pigs and poultry - current knowledge and directions for future research
Review. 6/10. Chemical and nutritional words.
Summary: Phytic acid found in grain reduces mineral uptake in body and also takes a lot of energy for the bird to process. Phytic acid binds itself easily to both minerals and pepsin (protein enzymes), but aren't absorbed by the body and are exerted through feces.
Recent advances in fermented feeds towards improved broiler chicken performance, gastrointestinal tract microecology and immune responses; a review
Summary: "Apart from improved nutritional properties, fermentation is associated with a high number of lactic acid bacteria (LAB), a low pH and a high concentration of organic acids. It has been shown that these latter features alone or in combination, may protect the feed from pathogen contamination prior to feeding, benefit chicken gastrointestinal health and chicken growth and development."
Effects of Delayed Feed Intake on Body, Intestine, and Muscle Development in Neonate Broilers
Study. PDF. 7/10. It's enough to read introduction and results
Summary: Depriving chicks of food the first 2 days post-hatch reduced their body weight at day 6 compared to chicks that got access to food right away. Chicks deprived of food lost weight the first 2 days, and their intestinal and muscular development were put on hold until the got access to food.
Pathology of gout in growing layers attributed to high calcium and protein diet
Autopsy of mass-death. 7/10. Anatomy and pathology
Summary: Broiler chicks from a case of mass-death were investigated. The result showed visceral gout. Analysis of feed samples showed 23.4% protein and 3.5% calcium, and this combined was thought to be the reason for the death. Similarly, another study: Clinicopathology of gout in growing layers induced by high calcium and high protein diets (abstract only) found that high calcium particularly and in combination with high protein caused visceral gout in non-laying chickens.
Nutrient Requirements of Poultry
Book. 4-8/10. Some parts are moderately easy, some are very specific.
Summary: This is a 157 page BOOK. It describes components in poultry feed, specific percentage requirements of different poultry, deficiencies and toxins and how to recognize them, and composition of feedstuff. Not something you read cover-to-cover, but a useful guide. It's from 1994, so a little out-dated.
Vitamin Nutrition for Poultry
Internet page. 2/10.
Summary: Comprehensive list of all vitamins, including explanation of deficiencies.
Nutritional Qualities of Grains
I'm gonna leave this here even if it's not a research article. It's a table that shows the difference in nutritional values in various grains. What this particularly shows is that oats have different values of micro nutrients than other grains - especially calcium (higher) and niacin (lower). The niacin content is of importance to ducks. Corn have significantly lower levels of calcium than other grains, but much higher in sodium.
Milestone in avian coccidiosis research: a review
Review. 6/10. Latin names, pathology.
Summary: History of our understanding of coccidiosis.
Marek's disease in chickens: a review with focus on immunology
Review. 8/10. Pathology and biology.
Summary: A difficult read for "laymen", but contains loads of information on what Marek's is, how it works and how the immune system combats is, including vaccination.
Salmonella Knowledge, Attitudes and Practices: A Survey of Backyard Poultry Owners Residing in Seattle, Washington and the Surrounding Metropolitan Area
Study. 2/10. Recommended
Summary: Backyard poultry holds the risk of carrying and transmitting pathogens as salmonella not only to their owners directly, but also throu 3rd party exposure. Many of us have birds because we want to interact with them, both being with them in the yard, having them in our house and petting them. Remember that this risks transmitting illnesses, and put in place hygiene practices for everyone that has contact with the animals, eggs and poop.
Veterinary Manual - Poultry
Internet site. Overview of poultry diseases with description, clinical findings, treatment etc.
Historic Perspective: Prebiotics, probiotics, and other alternatives to antibiotics
Review. 4/10. Latin names.
Summary: Antibiotic-resistance due to over- and misuse of antibiotics causes world wide concerns, and many alternative ways to handle bacterial illnesses are being investigated. Prebiotics; using "good" bacteria to fight bad. Probiotics; non-digestible food ingredients that promotes good bacteria. Bacteriophages. Bacteriocins. Phytotherapeutic; plant extracts and essential oils.
Neurobiological Basis of Sensory Perception: Welfare Implication of Beak Trimming
Review. 4/10. Biology expressions.
Summary: De-beaking of layer hens are a common practice to prevent feather picking and cannibalism. The beak doesn't only have blood vessels and nerve endings, it's an important sensory organ that enables the chicken to feel like we do with our hands. Recently de-beaked chick have trouble finding and identifying food, and adults perform less feather preening. After removal some hens can suffer from long term pain and scar tissue. Debating whether it's possible that individuals can suffer from Phantom Limb Pain similar to that of amputee's. Further reading on the anatomy of chicken bills: The bill tip organ of the chicken
Incidence of Wing Deformities (Angel Wing) Among Masked Boobies at Clipperton Island: Life History Consequences and Insight into Etiology
Summary: A number of chicks (0-2 years) with angel wing was observed in a colony of Masked Boobies on an isolated island. The authors lists the different things thought to cause angel wing; genetics, excess protein, toxins, physical damage, and none of them fit. They conclude that malnutrition due to a short term mass-starvation was the underlying cause.
In this short paper, Angel Wings Syndrom in Swans (google scholar, follow PDF link), they treat some swans with angel wing presumably caused by excess feeding of bread etc. Blood analysis showed high levels of sodium and low levels of calcium.
Diatomaceous earth (DE)
A lot of people use DE in dustbaths to help with external parasites. It's also used as a food additive as an aid against aflatoxins and intestinal worms. DE consists of mostly amorphous silica, though contamination with crystalline silica during manufacturing is common. Crystalline silica is a health hazard when inhaled, causing silicosis. There have been several studies of industry workers in DE-mines, regarding exposure to crystalline silica. One study in particular followed workers from 1942 to 1994, that is re-evaluated many times, like here: Crystalline silica exposure and lung cancer mortality in diatomaceous earth industry: a quantitative risk assessment. It shows a correlation between not only lung damage and pneumoconiosis, but also lung cancer from years of exposure to the toxic silica dust.
Health hazards due to the inhalation of amorphous silica focuses on separating the effect of the two different silica structures. The global variability of diatomaceous earth toxicity: a physiochemical and in vitro investigation and the previous link both lists animal experiments of silica dust inhalation. No birds or poultry have been tested. Inflammation, emphysema and granulomas were some of the consistent findings. Regression of illness happened when the animals were no longer exposed.
Nothern fowl mite control evaluations using liquid formulations of diatomaceous earth, kaolin, sulfur, azadirachtin and Beauveria bassiana on caged laying hens
Study. 3/10. Tables and math
Summary: "The materials can be listed in declining order of effectiveness for NFM as follows: sulfur > neem > kaolin clay > DE > Beauveria." See also: Housing and dustbathing effects on northern fowl mites and chicken body lice (abstract only) "All materials (DE, kaolin clay and sulphur) reduced ectoparasites on user hens by 80-100% after 1 week of dustbox use. Diatomaceous earth and kaolin failed to reduce ectoparasites on non-user hens, and ectoparasites on user hens recovered after dustbox removal. A sulphur dustbox eliminated mites from all hens (including non-users) within 2-4 weeks."
Effect of diatomaceous earth on the performance and blood variables of broiler chicks during experimental aflatoxiosis
Summary: Aflatoxins can be present in feedstuff and cause adverse effects on animals. DE is suggested to both reduce the level of aflatoxins in feed and help absorb the toxins when ingested. This study show that the effect of feeding DE to toxin-infected broilers is little to insignificant.
Effect of diatomaceous earth on parasite load, egg production, and egg quality of free-range organic laying hens
Summary: Two strains of commercial layer hens were fed DE and provided dust baths. Some form of internal parasites had lower levels in DE-fed birds of the weakest strain of hens. In the strongest strain, there were no difference. DE was effective in controlling northern fowl mites, with hens supplied DE having less parasite count. Some of the hens fed DE maintained their body weight better, and also ate more.
Early experiences matter: a review of the effects of prenatal environment of offspring characteristics in poultry
Summary: Many factors influence the chicks even before they hatch. Any nutritional irregularities within the hen will effect the chick either positive (supplements) or negative (deficiencies). Hormone levels will also be transferred into the egg, increased level of the stress hormone corticosterone has in particular showed detrimental, long lasting effects on the chick. Mild outside stressors during incubation, however, seem to be positive in the way chicks handle stress after hatch, like episodes of heightened or lowered temperature.
Breeding Biology of Muscovy duck Cairina moschatain Natural Incubation:The Effect of Nesting Behavior on Hatchability
Study. PDF. 2/10.
Summary: The natural incubation of Muscovy Ducks were followed for several years. Results: The two tings that affected hatchability the most were time from eggs were laid to incubation, and eggs laid after incubation had started. They also found that no access to swimming water didn't affect hatch rate, indicating that wetting the eggs during incubation is not necessary. There were no aggressiveness between ducks sharing the same nest.
Embryonic development and the physiological factors that coordinate hatching in domestic chickens
Review. 6/10. Biological language
Summary: How embryos develop including different sensory systems. Especially focused on factors around synchronized hatching, such as sound communication between the embryos.
Figures cited in the article found here: A series of normal stages in the development of the chick embryo (PDF) from page 250.
The Golden Egg: Nutritional Value, Bioactivities, and Emerging Benefits for Human Health
Review. 5/10. Biology expression and numbers.
Summary: Everything you could possible want to know about what's in an egg.
IFAS paper. 2/10.
Summary: Egg shell-, albumen- and yolk-quality and causes for abnormalities. Easy and useful tables.
Dietary factors improving eggshell quality: an updated review with special emphasis on microelements and feed additives
Summary: The availability and uptake of minerals are of special importance to egg shell quality. The levels of calcium, phosphorus, vitamin D3, magnesium and zinc need to be right and in balance. Pre-and probiotics as well as some essential oils can improve mineral uptake in the body.
Poultry Egg Incubation: Intergrating and Optimizing Production Efficiency
Summary: Egg incubation 101. Heat-, water- and gas transfer explained. The importance of correct humidity, temperature and air quality in incubator.
Influence of temperature and humidity manipulation on chicken embryonic development
Study. 4/10. Statistics and tables.
Summary: Control group were incubated at 37.8 C and 50-55 % humidity. 4 groups were tested; A incubated at 38.9 C, B at 36.7C. C incubated with 60-65 % humidity, D with 40-45 % humidity. Embryos were checked and tested throughout the incubation. The biggest differences were from the temperature changes, with high early mortality and signs of embryonic stress and malformations. Group D had high late mortality. Personally I think they should have gone even further with the humidity tests to see any difference, as low as 30 and high as 70%.
Artificial Incubation of Muscovy Duck Eggs: Why Some Eggs Hatch and Others Do Not
Summary: Duck eggs have a noticably lower hatch rate in articficial conditions than natural. In this study they find out that the eggs with late death and the ones that needed help were smaller in length and had lower metabolic rate on day 31 than the normal hatchers. They hypothesize that cooling helps the bigger eggs regulate egg temps, while it can be detrimental to smaller eggs. The eggs helped were also more rounded than the normal ones. Could it be that a duck mother pays more attention to the individual needs of the eggs?
Thanks to @Shadrach for providing articles!
If anyone else has interesting articles (preferably open access), feel free to comment or contact me.