Individual Hens Research Articles

Effects of Induced Molting on the Well-Being of Egg-Laying Hens

Induced molting in egg-laying hens is an important method for maximizing hen egg production and quality as well as hen health in commercial settings; however, there is growing societal concern over its effects on hen well-being. Using individual hens as their own controls, this research examined the behavior of hens subjected to different treatments of induced molting under premolt, molt, and postmolt conditions. Cage pecking increased in fast-induced subjects and aggression increased in fast-induced and nonfast-induced subjects during the molt. Gakel calling and several aspects of its acoustic structure were much higher during the molt condition in fast-induced subjects only. These data suggest that nonfast-induced molting treatments provide an effective method for inducing molting in hens and improving their well-being by minimizing discomfort due to food deprivation. In addition, these data further support that gakel vocalizations in hens may serve as an effective indicator for assessing well-being in a species otherwise behaviorally stoic in expressing stress or discomfort.

Effects of drinking water treatment on susceptibility of laying hens to Salmonella enteritidis during forced molt

Feed deprivation is used in the layer industry to induce molting and stimulate multiple egg-laying cycles in laying hens. Unfortunately, the stress involved increases susceptibility to Salmonella enteritidis (SE), the risk of SE-positive eggs, and incidence of SE in internal organs. Leghorn hens over 50 wk of age were divided into 4 treatment groups of 12 hens each in experiment 1 and 3 treatment groups of 12 hens in experiments 2 and 3; hens were placed in individual laying hen cages. Treatment groups were 1) nonmolted (NM) and received feed and distilled water for 9 d, 2) force molted by feed removal for 9 d and received distilled water, 3) force molted by feed removal for 9 d and received 0.5% lactic acid (LA) in distilled water. An additional group (4) in experiment 1 only was force molted by feed removal for 9 d and received 0.5% acetic acid in distilled water. Seven days before feed removal hens were exposed to an 8L:16D photoperiod, which was continued throughout the experiment. Individual hens among all treatments were challenged orally with 10(4) SE on d 4 of feed removal. When compared with the NM treatments, weight losses were significantly higher in the M treatments, regardless of water treatments. When compared with NM treatments, crop pH was significantly higher in the M treatment receiving distilled water. Crop pH was reduced to that of the NM controls by 0.5% acetic acid in the drinking water. No consistent significant changes were observed for volatile fatty acids. The number of hens positive for SE in crop and ceca after culture and the number of SE per crop and per gram of cecal contents were higher in the M treatments, when compared with the NM treatments, but there was no effect of addition of either of the acids to the drinking water. Additional research using different acid treatment regimens may provide a tool for reducing the incidence of SE in eggs and internal organs during and following molting of laying hens.

Reduction of Salmonella enterica serovar enteritidis colonization and invasion by an alfalfa diet during molt in Leghorn hens

The standard method for molting to stimulate multiple egg-laying cycles in laying hens is feed deprivation. However, the physiological changes within hens caused by feed deprivation increase susceptibility of the hens to Salmonella enterica serovar Enteritidis (SE) infection. In an effort to develop an alternative method to induce molting without increasing susceptibility to SE, an alfalfa diet was compared with the standard molting method for the level of ovary regression and SE colonization. Hens over 50 wk of age were divided into 3 treatment groups (12 hens/group): nonmolting by normal feeding (NM), molting by feed deprivation (M), and molting by alfalfa diet (A). Individual hens on all treatments were challenged orally with 10(5) cfu of SE on the fourth day after feed changes and were analyzed for ovary weight and SE colonization or invasion in crop contents, cecal contents, liver, spleen, and ovary on the ninth day. In 3 of the 4 trials, there was a significant decrease in SE colonization of the crop between the alfalfa diet (A) and the feed deprived molt (M). In most of the 4 trials, there was a significant reduction in SE infected organs in birds fed the alfalfa diet (A) compared with birds undergoing feed deprived molt (M). Most of the trials showed no significant difference in overall SE between A and NM. Therefore, the results of this study suggest that an alfalfa diet has the potential to be used as an alternative method for forced molting, without increasing the incidence of SE in eggs and internal organs.

A cross-sectional study to investigate the occurrence and distribution of intestinal spirochaetes ( Brachyspira spp.) in three flocks of laying hens

A cross-sectional study was conducted on a commercial egg-producing farm with a history of wet litter. A total of 600 fresh caecal faecal samples were obtained from under cages of laying hens in three sheds each containing flocks of ∼5400 hens. Samples were cultured for intestinal spirochaetes, and growth on the primary isolation plate was observed under a phase contrast microscope and subjected to PCRs specific for the intestinal spirochaetes Brachyspira intermedia and Brachyspira pilosicoli. Spirochaete isolates obtained in pure culture were assessed for their ability to cause haemolysis on blood agar and to produce indole, and were typed using pulsed field gel electrophoresis (PFGE). A 1250 base pair portion of the 16S rRNA gene of three B. intermedia and five unidentified isolates was sequenced, and the sequences compared with those of other Brachyspira species. Overall, 121 (20.2%) of the faecal samples contained spirochaetes as determined by growth on the plate and microscopy. Using PCR on the primary growth from these positive samples, 43 (7.2% overall) were shown to contain B. intermedia, 8 (1.3%) to contain B. pilosicoli, and 70 (11.7%) were PCR negative. Only 24 isolates of B. intermedia and five isolates of unknown species were obtained in pure culture. Comparative analysis of the 16S rRNA gene sequence identified the non- B. intermedia isolates as belonging to the proposed species “ Brachyspira pulli”. PFGE analysis of the B. intermedia strains identified them as having four major banding patterns. Individual patterns were found in hens from different flocks, suggesting cross-transmission of strains between flocks. No environmental sources of infection were identified. The youngest flock had a significantly lower level of colonisation with B. intermedia than the flock of intermediate age ( P = 0.004), suggesting that following initial infection of individual young hens on this farm there was amplification and transmission of infection amongst members of the flock.

Habitat predicts losses of red grouse to individual hen harriers

Summary Hen harriers Circus cyaneus prey on red grouse Lagopus l. scoticus and high breeding densities of harriers can limit the number of grouse available for shooting in the autumn. Ultimately, grouse hunting contributes to the maintenance of heather moorland, an ecologically important habitat for biodiversity in general and hen harriers in particular. Predation rates vary widely among harrier individuals. Understanding which factors influence this variation would be useful to target management to mitigate the effect of harriers on grouse, such as diversionary feeding. We used a simple habitat‐based approach to test whether we could identify harrier nests to which most grouse were delivered. Using remote sensing habitat data, we tested whether delivery rates of dead grouse to the nest by hen harriers were higher for those pairs nesting in sites with more heather Calluna vulgaris. A relationship between heather cover and grouse delivery rates might have been expected as grouse densities were correlated with heather cover. After adjusting for annual variation in grouse abundance, the rate at which grouse were delivered to harrier nests was positively associated with the proportion of heather cover within 2 km of harrier nests. This was primarily due to the positive effect of heather cover on female delivery rates. This result allowed us to use habitat data to predict the harrier nests to which most grouse chicks would be delivered. Comparison of predictions of the model with observations of food delivery to nests indicated that, in terms of grouse chick delivery, the model correctly predicted the top 50% of harrier nests in five of six years. We undertook an experiment where carrion was provided to certain harriers at nest sites, in order to decrease their predation on grouse. Data from this experiment showed that when harriers were given diversionary food, the relationship between grouse predation rate and habitat was removed, with grouse predation reduced to negligible levels in most cases. This demonstrated the increased benefit of feeding birds with the highest proportion of heather cover within 2 km of their nest sites, rather than feeding birds at random within the conflict population. Synthesis and applications. The amount of heather cover around hen harrier nests can be used to predict which pairs will predate most grouse within a population. This information should facilitate targeted management practices, which may accrue greater benefit for grouse stocks and potentially reduce the conflict between grouse shooting and conservation of biodiversity.

Introduction

Avian osteoporosis has been recognized as a problem in the laying hen industry for at least 45 years. The onset of this disease in individual hens decreases bird welfare, eggshell quality, and egg production by the flock but also increases the incidence of broken bones and lameness. Webster presents an overview of the welfare implications of osteoporosis in laying hens. This author discusses the perception of pain by birds, and relates the lesions associatedwith osteoporosis to the degree of pain perceived by the bird. Attention is also given to humane handing and disposition of spent hens.The large demand for Ca for eggshell formation compounds the inability of actively laying hens to deposit new structural bone. The symposium paper presented by Whitehead reviews basic avian bone biology, with special reference to the factors involved in development and prevention of excessive structural bone loss in laying hens.Medullary bone is a unique form of labile bone found in egg-laying birds; potential methods to optimize medullary bone reserves and utilization by the hen are presented.Estrogen plays an important role in the regulation of Ca metabolism in laying hens. Beck and Hansen discuss the metabolic functions of estrogen in the laying hen, and address the topic of changes in estrogen synthesis and receptor numbers as the hen ages. As in humans, simple nutritional interventions are of limited use in preventing avian osteoporosis. Therefore, a deeper understanding of the factors that regulate metabolism in laying hens is required.Because of the serious implications for laying hen productivity and welfare, much research over the years has been conducted into the causes and prevention of osteoporosis. Measurements of production such as egg numbers and eggshell quality have been used to indirectly assess the effects of dietary, pharmaceutical, or management treatments on Ca metabolism of laying hens. Direct measurement of the skeletal health of laying henswas almost always conducted postmortem. Traditionally, measurements of avian bone quality involved sacrificing a portion of the population at various times throughout or at the end of a trial and conducting destructive tests on the bones. These tests included measurement of specific bonemass and volumetric density, breaking strength, and bone ash andmineral measurements. Although many important fundamental discoveriesweremade using these techniques, the availability of modern analytical techniques and equipment has spurred an increase in the use of noninvasive testing of bone quality of laying hens. Fleming and co-workers present results of their studies using quantitative ultrasound, in which the speed of sound through a bone is dependent upon the density of the specific location on the bone in question (amplitude-dependent speed-of-sound ultrasound). Hester et al. offer details on their use of dual-energy x-ray absorptiometry to assess bone density of entire bones. X-rays of 2 distinct energies are passed through the bone and recorded, and the attenuation of each of the energies by the bone is used to calculate a two-dimensional radiographic density. Korver et al. communicate their work with quantitative computed tomography. This technique involves passing an x-ray at numerous angles through a fixed point on a bone. The resultant cross-sectional image allows calculation of a true volumetric mineral density as well as spatial distribution of bone mineral at that specific crosssection of bone.The previous 3 papers compare each of the newer noninvasive

Garlic Powder as Blood Serum and Egg Yolk Cholesterol Lowering Agent

To assess the effect of supplying garlic powder (GAR) in the diet on blood serum and egg yolk cholesterol, maize-soybean diets supplemented with 0 (NC), 0.5 (GAR0.5), 1 (GAR1),1.5% (GAR1.5) as well as Tylosin (PC), were given to 200 hens as a completely randomized experiment throughout a 10 weeks production period. Blood samples for serum cholesterol determination were collected from wing vein of individual hen with two weeks intervals, and egg were collected once a week and subjected to cholesterol assay. Supplementation of diets with garlic powder and Tylosin had significant (p<0.01) effects both on serum and egg yolk cholesterol. The lowest serum cholesterl was obtained with GAR1, while the NC gave the highest level of cholesterol. A similar trend was observed with yolk cholesterol, in which GAR1 and NC were the treatments with the lowest and highest cholesterol. The results showed that inclusion of garlic powder significantly (p<0.01) decreased yolk weight, though there were no differences between the different level of the garlic powder. The correlation between yolk and serum cholesterol was negative and low (r=-0.09, p<0.05). In conclusion the results of this study clearly demonstrated that, there is, considerable advantages in using garlic powder rather than chemical reagents in hen rations and there would be even greater advantage both in results and in cost for either poultry industry and consumers, if garlic powder fed to the hens.

Amino acid nutrition in egg production industry

ABSTRACTThe egg production industry is facing various problems that need to be solved. For amino acid nutrition to achieve scientific and economical feeding of laying hens, it is necessary to elucidate the content, digestibility, or availability of nutrients of feedstuffs and feeds and the requirement of amino acids for laying hens. In addition, improvement to quality of eggs and meat of spent hens, methods of management and development of new feedstuffs are essential. For sustainable animal production, decrease in excreta and animal welfare should be studied. The real‐time determination of content and digestibility of amino acids in feedstuffs are essential for formation of feeds. Recent advances in the near infrared reflectance analysis will be able to determine the content, digestibility and availability of nutrients in feedstuffs and feeds, if we have a supplemental amount of conventional analysis to define the calibration population. The amino acid requirements are affected by various factors. Therefore the method to quickly and exactly determine amino acid requirements in response to various factors is necessary. By using plasma free amino acid concentration as a criterion, it is possible to determine amino acid requirements in various conditions of laying hens within a short experimental period, repeatedly using the same animals. Because the amino acid requirements differ among individual animals, it should be expressed as grams per hen per day. Practically, it is impossible to formulate various feeds for individual hens. The various expressions have been developed and these expressions have advantages and disadvantages. The nitrogen excretion of laying hens is easily reduced by reducing dietary nitrogen levels and restricting the feed intake. The availability of amino acid may be improved by feeding management, and supplementing enzyme, but the quality of eggs and meat of spent hens and welfare of laying hens are not affected by amino acid nutrition.

Social discrimination and aggression by laying hens in large groups: from peck orders to social tolerance

Domestic fowl ( Gallus gallus domesticus) naturally live in small groups, with a dominance hierarchy (pecking order) which is most likely based on establishment fights, followed by remembered assessment of status involving individual recognition. In larger groups, this system is thought to break-down, and hens may adapt by becoming less aggressive, or by restricting their movements to defined ‘territories’. In the present study, we tested the ability of laying hens living in groups of 10 and 120 to discriminate flockmates from unfamiliar birds. Subjects were presented in test cages with vertical bars, positioned outside the home pens in one of two places. Sixteen subject hens from each group size were presented to their home group (familiar) and a different group of the same size (unfamiliar) on each of four test days. For half of the test days, the groups were swapped between pens to control for the effect of location. Regardless of the location, hens in small groups discriminated between familiar ( F) and unfamiliar ( U) subjects by showing more aggression towards unfamiliar hens (attempted fights: F=18.8%, U=56.3% of tests; all aggression: F=60.9%, U=85.9% of tests). In large groups, the overall level of aggression towards subjects was reduced in that attempted fights were rare ( F=0.0%, U=4.7% of tests), and aggressive outcomes were no different in response to unfamiliar or familiar hens ( F=46.9%, U=42.2% of tests). The absence of flockmate/stranger discrimination in these large groups makes it unlikely that these hens had a conventional pecking order based on individual recognition within the group. Regardless of the location of the test cage beside the pen, certain individual hens in large groups were more likely to approach it, showing no evidence that hens have limited ‘territories’ within the pen. In large groups (but not in small), hens that approached and were aggressive were both heavier and had larger combs than the subjects. Taken together, these findings are consistent with the idea that in large groups hens become less aggressive and may change their social system to one where dominance is determined through direct assessment and ‘status signalling’ rather than the remembered individual assessment of a small group pecking order.

Genotype analyses of Campylobacter isolated from distinct segments of the reproductive tracts of broiler breeder hens.

Campylobacter isolated from feces and from the oviduct of six broiler breeder hens were genotyped by using flaA SVR DNA sequence analyses. A diversity of genotypes was observed among fecal and oviduct isolates. Comparison of isolates from the oviducts of individual hens revealed variable results. In three cases (hen 2, hen 3, and hen 6), analyses indicated that isolates from all regions of the individual hen's reproductive tract were closely related; isolates from hen 1 and hen 4 were diverse. Comparison of the Campylobacter isolates between hens revealed that in two cases, hens 1 and 3 and hens 4 and 6, certain isolates possessed identical flaA SVR sequence types. Comparisons of Campylobacter isolates recovered from a distinct region of the oviduct were found to have increased diversity as sampling progressed down the oviduct. This study further demonstrates that Campylobacter is present within the reproductive tract of breeder hens and that this presence may enable vertical transmission of Campylobacter from the breeder hen to the broiler offspring.

How important is social facilitation for dustbathing in laying hens?

Hens in a group usually synchronize dustbathing, such that when one hen starts to dustbathe she will often be joined by others. The sight of another hen dustbathing could thus possibly act as a stimulus increasing motivation for dustbathing, with important implications for hens in furnished cages, where the size of the dustbath normally allows only one hen to dustbathe at a time. If a hen is more motivated to dustbathe when she can see another hen dustbathing but she cannot get access to the litter since the dustbath is occupied, frustration may arise. The aim of this study was to investigate the effect of social stimuli on dustbathing motivation. Pairs of hens were exposed to one of three stimuli while being thwarted of dustbathing and they were thereafter given access to dustbathing material. The stimuli were (1) the sight of other hens dustbathing (DB-HEN), (2) the sight of a dustbath with other hens not dustbathing (NODB-HEN) and (3) the sight of a dustbath only (NO-HEN). Twelve pairs of hens were tested both deprived and non-deprived of litter in a balanced within-subject design. Irrespective of deprivation state, hens walked more and spent more time facing the stimulus in DB-HEN than in NO-HEN, and when they were not deprived they also walked more in DB-HEN than in NODB-HEN. Subsequent dustbathing behaviour when hens were given access to litter after the stimulus exposure was unaffected by the type of stimuli. We suggested that subtle effects of social stimuli on dustbathing motivation may have been masked by the effect of long litter deprivation and that it may be important for the birds to be able to join the stimulus birds to dustbathe together. For these reasons we repeated the experiment with individual hens and with a shorter litter deprivation time and a shorter stimulus exposure, after which the test hen was allowed to join the stimulus hen. Furthermore, in this second experiment hens were tested only in DB-HEN and NODB-HEN treatments. We found more displacement preening and less time facing the stimulus in DB-HEN than in NODB-HEN, but dustbathing behaviour was still unaffected by previous social stimuli. In summary, dustbathing behaviour of the test hens was not affected by seeing other hens dustbathing, but increased walking and displacement preening indicated a possible change in the motivation of test hens observing other dustbathing hens.

Recovery of Campylobacter from segments of the reproductive tract of broiler breeder hens.

Three groups of >60-wk-old broiler breeder hens were assessed for the presence of Campylobacter within segments of the reproductive tract. In the first group, after stunned, the hens were bled, scalded, and defeathered, the reproductive tracts were aseptically excised from 18 hens, six from each of three adjacent floor pens that were feces positivefor Campylobacter. The reproductive tract segments (infundibulum, magnum-isthmus, shell gland, vagina, and cloaca) were pooled by pen. In the second group, 10 individual hens were sampled from the pens; the reproductive tract was divided into the following segments: magnum, isthmus, shell gland, vagina, and cloaca. For the third group, hens were obtained from two commercial farms that had been determined to be feces positive for Campylobacter, and the reproductive tract was divided into five segments, as described for the second group. Segments of the reproductive tract were placed into sterile plastic bags and suspended 1:3 (w/v) in Bolton enrichment broth, and serial dilutions were plated (0.1 ml) onto Campy-Cefex agar. The agar places were incubated at 42 C for 24 hr in a microaerobic atmosphere. In group 1, the pooled reproductive tract segments for hens from pen A were Campylobacter positive for the shell gland, vagina, and cloaca; hens from pen B were positive for the cloaca only; and hens from pen C were positive for the magnum-isthmus and doaca. In the second group, 9 of 10 cloaca samples were Campylobacter positive. Commercial hens in group 3 had campylobacter-positive cloaca samples (12/12), vagina (10/12), shell gland (7/12), isthmus (2/12), and magnum (4/12). Campylobacter colonization of the reproductive tract of the hen could enable vertical transmission of Campylobacter from the hen to the chick.

Practical and economic advantages of choice feeding systems for laying poultry

Poultry can be managed under different feeding systems, depending on the husbandry skills and the feed available. These systems include the following: (1) a complete dry feed offered as a mash ad libitum; (2) the same feed offered as pellets or crumbles ad libitum; (3) a complete feed with added whole grain; (4) a complete wet feed given once or twice a day; (5) a complete feed offered on a restricted basis; (6) choice feeding. Of all these, an interesting alternative to offering complete diets is choice feeding which can be applied on both a small or large commercial scale. Under choice feeding or “free-choice feeding” birds are usually offered a choice between three types of feedstuffs: (a) an energy source (e.g. maize, rice bran, sorghum or wheat); (b) a protein source (e.g. soyabean meal, meat meal, fish meal or coconut meal) plus vitamins and minerals and (c), in the case of laying hens, calcium in granular form (i.e. oyster-shell grit). This system differs from the modern commercial practice of offering a complete diet comprising energy and protein sources, ground and mixed together. Under the complete diet system, birds are mainly only able to exercise their appetite for energy. When the environmental temperature varies, the birds either over- or under-consume protein and calcium. The basic principle behind practising choice feeding with laying hens is that individual hens are able to select from the various feed ingredients on offer and compose their own diet, according to their actual needs and production capacity. A choice-feeding system is of particular importance to small poultry producers in developing countries, such as Indonesia, because it can substantially reduce the cost of feed. The system is flexible and can be constructed in such a way that the various needs of a flock of different breeds, including village chickens, under different climates can be met. The system also offers a more effective way to use home-produced grain, such as maize, and by-products, such as rice bran, in developing countries. Because oyster-shell grit is readily available in developing countries at lower cost than limestone, the use of cheaper oyster-shell grit can further benefit small-holders in these countries. These benefits apart, simpler equipment suffices when designing and building a feed mixer on the farm, and transport costs are lower. If whole (unground) grain is used, the intake of which is accompanied by increased efficiency of feed utilisation, the costs of grinding, mixing and many of the handling procedures associated with mash and pellet preparation are eliminated. The choice feedstuffs can all be offered in the current feed distribution systems, either by mixing the ingredients first or by using a bulk bin divided into three compartments.

Limited Day to Day Variation of IgY Levels in Eggs from Individual Laying Hens

Laying hens are highly efficient producers of polyclonal antibodies (PAbs). These antibodies are transported to the egg yolk in large quantities from the blood of laying hens. The IgY concentration in the egg yolk is important to protect the newly hatched chick against infections and it is also an important factor for the production of yolk antibodies for commercial purposes. A single egg yolk contains approximately the same amount of IgY as 30 ml of blood. This is a significant loss of antibodies for an animal the size of a hen. We have studied the IgY levels in egg yolk. We found low day to day variability. There was no decrease in IgY levels at the end of the egg laying cycle and there was no correlation between IgY concentration and egg production.

The Relationship between the Magnitude of the Specific Antibody Response to Experimental Salmonella enteritidis Infection in Laying Hens and Their Production of Contaminated Eggs

Detecting infected laying flocks is a vital part of many efforts to control egg-associated transmission of Salmonella enteritidis to humans. The relationship between the development of a specific antibody response in infected hens and the deposition of S. enteritidis in eggs is important for establishing the epidemiologic relevance of serologic testing methods. In two trials, laying hens were infected with large oral doses of phage types 13a and 14b isolates of S. enteritidis. Approximately 38% of all infected hens produced at least one contaminated egg, at an overall incidence of 5.2%, between 3 and 23 days postinoculation. As determined by enzyme-linked immunosorbent assay with an S. enteritidis flagellar antigen, 91.7% of inoculated hens produced specific serum antibodies. Although hens with very high antibody titers were associated with a significantly elevated frequency of egg contamination, a consistently direct relationship was not evident between the magnitude of the antibody responses of individual hens and the frequency at which they laid contaminated eggs. Accordingly, although serologic tests can be valuable screening tools for preliminary detection of S. enteritidis infections in poultry, the magnitude of the antibody responses detected in individual hens may not predict the overall risk of egg contamination associated with particular laying flocks.

Contrasts and Comparisons of Incentive Situations in Domestic Poultry

Understanding the way in which animals perceive important features of their environment, and how this information may be stored and used, underpins the study of the impact of husbandry systems on animal welfare. Research into incentive contrast in laboratory animals has indicated that they can store and use information about stimuli associated with situations or resources. If cognitive processes are used, the relevant stimuli associated with a resource or event are encoded, allowing comparisons to be made when the key stimuli are changed. The presence and quality of this comparison, negative or positive, can be ascertained by assessing the change in the animal's level of appetitive or operant responding in order to gain access to the situation on the subsequent trial. We wished to determine whether the presence of a sudden change in appetitive response, such as speed of approach to an area following a change in incentive features of a resource or event in that area, is shown by the domestic chicken. This would indicate the presence of a cognitive comparison of incentives. The magnitude of such a change may also provide a measure of the welfare impact of the change. In the first experiment, 16 groups of four broiler chicks were trained to run a maze to an area where they received a high quality test diet. After training, the test diet of eight groups was changed to a low quality diet that all groups had been receiving in their home pens. Compared to the control unchanged groups, the experimental birds took increasingly longer to run the maze on successive post-change trials; the decrease reaching significance on the fourth post-change trial (P &lt; 0.05). The behaviour of the chicks on the day of the change was indicative of frustration, with greater activity and redirected foraging shown (P &lt; 0.05). Although there was no definitive evidence of cognitive processing which would have been shown by an immediate decrease in approach speed, this may have been due in part to the testing of groups of chicks. However, the occurrence of a frustration reaction indicated that some cognitive representation of food quality may have been present. In a second experiment, individual adult hens were trained to run a runway for access to food or water, while food- or water-deprived, respectively. Every fourth trial in a total of 16 trials, access to the resource was thwarted by a clear plastic lid on the dish. Time taken to traverse the runway was significantly longer on the two trials following this experience (P &lt; 0.05), with no effect of repetition of thwarting (P &gt; 0.05), indicating that the experience of thwarting was aversive. These results indicated that chickens appear to be able to store and use information on incentives. Additionally, with appropriate experimental design, an incentive contrast paradigm might be used to assess birds’ perception of the quality of changes in incentives.

Temporal Characteristics and Incidence of Photorefractoriness in Turkey Hens

We conducted experiments to determine the incidence and temporal components of photorefractoriness (PR) in first-year turkey breeder hens after photostimulation. In turkey hens, PR may be defined as a lack of responsiveness to photoperiods that previously induced or maintained egg production and is characterized by a spontaneous cessation of lay, usually followed by molt, as well as an absence of nesting behavior. In one experiment, groups of hens were photostimulated with 18 h of light (L):6 h darkness (D) for 12, 16, 19, or 22 wk and then were exposed to 13L:11D photoperiods to induce a change in egg laying that allowed an evaluation of the photoresponsive state of each group of hens. In two other experiments individual hens were photostimulated continuously with 16L:8D for 24 or 45 wk, and the onset of PR was evaluated by the spontaneous cessation of lay. Data were collected for time to onset of PR, percentage incidence, duration of PR, and the time required for the transition from the photosensitive to the PR state.The earliest onset of PR occurred 7 wk after photostimulation, and the mean onset occurred at about 18 wk of photostimulation. Hens that expressed PR did so within an 18-wk period ending at 25 wk of photostimulation, but not all of these first-year hens expressed PR. Incidence of PR was variable at 59 and 89% in Experiments 2 and 3, respectively. The transition from a photosensitive state to an overt PR state, and therefore a laying to nonlaying state, occurred abruptly within a 2-wk period. Photorefractoriness was permanent during 45 wk of photostimulation for 11% of the PR hens. In the remaining 89% of hens, PR persisted for at least 14 wk (mean of 20.0+/-0.9) but it was not permanent, because they subsequently spontaneously recrudesced. That is, they spontaneously terminated PR. It was concluded that most, but not all, first-year turkey hens become PR and that the incidence is highly variable; PR may be relative or absolute, and absolute PR occurs abruptly but with a highly variable onset time. In most hens, PR is not permanent.

Domestic hens have declarative representations

It is generally considered that information can be stored either as a procedural or as a declarative representation. A devaluation technique was used to determine whether hens have declarative representations. Individual hens (Gallus gallus domesticus) were fed in an enclosure with two containers, each with a new food type. One of the food types was devalued by pre-feeding with that food, after which the hens were tested with empty food containers. The pre-feeding should only affect the choice of the hens if they have learned where a particular food type was (declarative representation) rather than “go left when coming into the enclosure” (procedural representation). A significant proportion of the hens went to the location previously occupied by the non-devalued food (seven out of eight). This supports the hypothesis that domestic hens can form declarative representations.

Monitoring northern fowl mites (Acari: Macronyssidae) in caged laying hens: feasibility of an egg-based sampling system.

Northern fowl mites were monitored on a caged-layer operation in southern California for 22 mo. Three experienced observers underestimated actual numbers of mites in the vent region approximately 80% of the time. Errors were higher for heavy infestations. Observer estimates were highly correlated with each other (r > 0.89, P < 0.01) and with mite numbers estimated by vent feather removal (r > 0.82, P < 0.01). Mites on hens varied between houses and over time. Molting consistently reduced mite numbers, but did not eliminate then in a flock. Long-term monitoring of individual sentinel hens demonstrated that some hens would support high numbers of mites for several months or more. Use of a new sequential hen sampling plan required approximately 1 min per hen, if mite numbers were estimated. At this site, treatment decisions often could be reached in < 20 min per house. Mite scores (index of estimated mites per hen) were well correlated with percentage of hens infested in both test houses. In a chronically infested house, prevalence of mites on eggs averaged 8.5%, with a range of 0-55%. Applications of tetrachlorvinphos-dichlorvos by the producer appeared to be based on mites on > about 20% of eggs. The chemical was marginal for controlling mites on hens (25% reduction in percentage of hens infested), but effectively reduced mites on eggs (95% fewer mites on eggs at 1 wk and 90% at 2 wk). When data were grouped by mite index score on hens, there was a strong relationship (r2 = 0.83, P < 0.01) between mite prevalence on eggs and the scores of the hens which laid them. Sampling 100 eggs evenly spaced in a house required < 7 min, and adult mites were easily seen. Sampling mites on eggs appears to be useful to localize at least high-level infestations, and egg-based sampling for mites merits further investigation.

Discrimination of multidimensional geometrical figures by chickens: categorization and pattern-learning

Japanese bantam hens were trained to discriminate between geometrical figures varying along four integral dimensions. Only one dimension predicted food: selections of sharp-cornered figures were reinforced, while selections of rounded figures were not. In experiment 1, hens were subsequently trained to discriminate between nine figure pairs in a simultaneous discrimination task. Because single pairs contained multiple redundant cues, whereas the relevant dimension was obvious only across stimulus pairs, the results revealed effects of both generalization and reversal learning. Accordingly, learning speed was enhanced for later discriminations. Experiment 2 tested the hens’ transfer performance to unknown pairs, following experience of 9 or 18 figure pairs. Four of seven hens showed reliable transfer after experience with 9 figures, but only three showed transfer after experience with 18 figures, indicating lower transfer with higher number of stimulus pairs learned. In experiment 3, hens were trained to discriminate 27 figure pairs. Discrimination ratios further decreased and the groups of pairs differed significantly in their ratios of discrimination. Individual hens’ pecking behaviour was analysed in relation to each dimension of single figures and in relation to relative differences in the levels of dimensions between paired figures. Hens were shown to be oriented towards irrelevant information and more towards relational and configurational than elemental and dimensional aspects. The results are discussed in the biological context of individual recognition in chickens’ dominance hierarchies, in which we suppose that chickens identify individual flock mates by representation of their visual pattern rather than by single characteristics.