In Ovo Olfactory Experience Influences Post‐hatch Feeding Behaviour in Young Chickens

In several mammalian species, prenatal exposure to odours can elicit later positive consummatory behaviour in response to substrates bearing that odorant. In birds, the sense of smell has been considerably underestimated, and very little is known about the effects of early sensory experience on the regulation of feeding behaviour. We tested the hypothesis that the feeding behaviour of the domestic chicken could be regulated by olfactory learning during the embryonic life. To that end, chicken embryos were exposed to an olfactory stimulus (blend of essential oil of orange and nature identical vanillin) from embryonic day (ED) 12 to ED20, and chicks were tested between 4 and 9 d of age. In short‐term choice tests, at day 4 and 5, chickens previously exposed to a low concentration (LC) of the olfactory stimulus spent a higher proportion of time eating a familiar or an unfamiliar food bearing the olfactory stimulus compared to non‐exposed control chickens. Conversely, chickens previously exposed to a high concentration (HC) of the olfactory stimulus were found to avoid all foods bearing the olfactory stimulus. On a 24‐ h time scale at day 7–8, LC and HC birds, but not controls, ingest significantly less familiar food containing the olfactory stimulus. This result indicated a long‐term effect of the early olfactory experience on feeding preferences. We demonstrated that chickens can utilize information from their pre‐hatch chemosensory environment to guide their later feeding behaviour. A pre‐hatch effect of the intensity of odour signals in the regulation of feeding behaviour is reported here for the first time.     

Maternal Diet Influences Offspring Feeding Behavior and Fearfulness in the Precocial Chicken

Background

In chicken, oils in the maternal diet confer a specific scent to the yolk. Embryos are known to perceive and memorize chemosensory signals of the surrounding environment; however, the potential impact of the maternal diet has not previously been investigated. In the present study, we hypothesized that chicken embryos memorize the chemical signals of the maternal diet and that this perceptual learning may orient subsequent feeding behavior of the hatchlings.

Methodology/Principal Findings

Laying hens were fed standard food enriched with 2% menhaden oil (MH group) or 2% soybean oil (controls). The scent of menhaden was significantly more detected in MH egg yolks than in control yolks by a human panel. We analyzed the development and behavior of offspring towards different types of food, bearing or not bearing the menhaden scent. When chicks were exposed to a 3-min choice test between the familiar food bearing the menhaden scent and the familiar food without menhaden, no effect of treatment was observed. In a 3-min choice test with unfamiliar food (mashed cereals) MH chicks showed a clear positive orientation toward the unfamiliar food bearing the menhaden scent. By contrast, control chicks showed a preference for the non-odorized unfamiliar food. MH chicks expressed higher emotional reactivity level than control chicks as expressed by food neophobia and longer immobility in a restraint test.

Conclusion/Significance

Chicks exposed in ovo to menhaden oil via the maternal diet preferentially oriented their feeding behavior towards food containing menhaden oil, but only when the food was unfamiliar. We propose that oil in the maternal diet engenders maternal effects and contributes to the development of behavioral phenotype in the offspring. In ovo chemosensory learning may have evolved to prepare precocial offspring for their environment. This suggests a common principle of embryonic chemosensory learning across vertebrate taxa.     

Pituitary adenylate cyclase activating polypeptide plays a role in olfactory memory formation in chicken

PACAP plays an important role during development of the nervous system and is also involved in memory processing. The aim of the present study was to investigate the function of PACAP in chicken embryonic olfactory memory formation by blocking PACAP at a sensitive period in ovo. Chicken were exposed daily to strawberry scent in ovo from embryonic day 15. Control eggs were treated only with saline, while other eggs received a single injection of the PACAP antagonist PACAP6-38 at day 15. The consumption of scented and unscented water was measured daily after hatching. Animals exposed to strawberry scent in ovo showed no preference. However, chickens exposed to PACAP6-38, showed a clear preference for plain water, similarly to unexposed chicken. Our present study points to PACAP's possible importance in embryonic olfactory memory formation.     

Effects of early embryonic bursectomy and opotherapic substitution on the functional development of the adrenocorticotropic axis.

Functional development of the adrenocorticotropic axis was inferred from plasma ACTH and corticosterone levels in intact and embryonically bursectomized (BFX) embryos and chicks from 8 days before to 56 days after hatch. Bursectomy was surgically made at 80 h of incubation and resulted in various alterations in developing adrenocorticotropic axis: ether stress-induced hormonal stimulation could be detected more precociously in BFX (day-6) than in intact embryos; the non stress-responsive period of newly hatched controls did not appear in BFX chicks; BFX young adult chicken exhibited quite smaller responses to stress than controls. In ovo injection of bursin (Lys-His-Gly-NH2) to 6- and 9-days old BFX embryos could restore normal adrenocorticotropic development provided convenient doses of tripeptide were used: administration of 100 fg or 100 pg of bursin was effective to restore normal hormonal levels at all stages studied whereas 100 micrograms was effective at embryonic stages only. The tripeptide Lys-His-Gly-NH2 is suggested as a possible signal from the immune B system directed at the hypothalamo-hypophysial-adrenocortical axis.     

Identification of stimuli and input pathways mediating food-attraction conditioning in the snail, Helix

Snails become conditioned by a single feeding episode to locate foods which they were unable to locate prior to feeding. To identify which of the different stimulus parameters of the food mediate learning, snails were presented with isolated stimulus components during feeding and re-tested the next day for their ability to locate the food. None of the individual components was sufficient to promote conditioning. Odor combined with a bulk stimulus conditioned the animals, as indicated by their subsequently locating the food. Elimination of the olfactory sensory inputs from the anterior and/or posterior tentacles prior to conditioning revealed that the acquisition of the olfactory memory requires olfactory stimulation of the sensory epithelia on the anterior tentacles. Recall of memory during olfactory orientation requires functional epithelia on the posterior tentacles, which suggests that the same odor is processed by different input pathways under different situations. Animals with the olfactory epithelia functional on the same side during conditioning and food searching were able to locate the conditioned food. Animals with different epithelia functional during conditioning and food searching failed, which suggests that olfactory memory is stored within one side of the nervous system and cannot be accessed from the contralateral side. Accepted: 28 November 1997     

Prenatal and early sucking influences on dietary preference in newborn, weaning, and young adult cats

Early experiences are of potential importance in shaping long-term behavior. This study examined the relative influence of prenatal and/or early postnatal experience of chemosensory stimuli on subsequent olfactory and dietary preferences of cats as newborns, at 9-10 weeks, and at 6 months. Cats were exposed to vanillin or 4-ethylguaiacol via their mother's diet either prenatally, postnatally, perinatally (prenatal and postnatal), or experienced no exposure to the stimuli (control). Newborns were given a two-choice olfactory test between the familiar "odor" and no odor; 9-10 week olds were tested for their preference between two food treats, one flavored with the familiar stimulus and the other unflavored; at 6 months, cats were given a choice of two bowls of food, one flavored with the familiar stimulus and the other unflavored. At all ages, cats preferred the familiar, and avoided the unfamiliar, stimulus. Perinatal exposure exerted the strongest influence on preference. Prenatal exposure influenced preference at all ages and postnatal exposure exerted a stronger effect as the cat aged. We conclude that long-term chemosensory and dietary preferences of cats are influenced by prenatal and early (nursing) postnatal experience, supporting a natural and biologically relevant mechanism for the safe transmission of diet from mother to young.     

Temporal changes in food preferences of wood mice (Apodemus sylvaticus L.)

Diet choice was determined for wild-caught wood mice (Apodemus sylvaticus L.), temporarily confined to cages in the field and offered a choice of 24–26 types of seeds and fruits in 2-h sessions throughout the night. The mice showed an overall preference for some foods over others. The set-up minimized influences on food preferences of predation risk, hunger, food availability and competition. Variation in food preferences was not attributable to differences between individuals, but followed a temporal pattern. The variety of foods eaten showed a bimodal pattern with peaks corresponding to the two most active periods at the beginning and end of the night. Both the amount of food eaten and variation in the amount diminished from the first to the second active period. An expected selection for carbohydrates early in the night and proteins at the end of the night was not found, but sugars were selected for early in the night. These results are discussed in relation to the conflict between an animal's continuous energy requirements and the essentially periodic activity of foraging.     

Reversibility revisited: Stimulus-dependent stability of filial preference in the chick

The reversibility of filial preferences was studied in domestic chicks, Gallus gallus domesticus, using an artificial as well as a more naturalistic imprinting stimulus. Day-old chicks were exposed for 2 h to either a rotating stuffed jungle fowl or a rotating red box. Two hours later their preferences were tested in a simultaneous choice test (test I), involving the box and the fowl. The next day, the chicks were trained and tested (test II) as before, except box-trained chicks were now exposed to the fowl and vice versa. In three different experimental groups, the relative attractiveness of the two stimuli (as measured in test I) was varied by altering the light intensity of the red box. In the chicks trained with the box and subsequently exposed to the fowl, there was a significant decrease in mean preference for the box from test I to test II. In contrast, the preference of the chicks trained with the stuffed fowl were not affected by subsequent exposure to the red box. This differential reversibility was also found when, in test I, the preference for the box was significantly higher than the preference for the fowl. These results support a model of the formation of filial preference as an interaction between acquired preference and a developing predisposition for a particular class of stimuli.     

Domestic hen chicks' conditioned place preferences for sound

Food and sounds (white noise, a food call and the sound of other chicks) were used in an attempt to establish conditioned place preferences with domestic hen chicks. Thirty-two chicks were randomly allocated to one of the 4 groups, and exposed to a 3-compartment apparatus to establish a baseline of their movements across 4 15-min sessions. They were then confined to one compartment and provided with free access to food or exposed to one sound for 15 min and then they were confined to the alternate compartment with no food or sound for 15 min. This process was repeated 3 times. Post-conditioning test sessions showed a conditioned place preference towards the area associated with food and away from the area associated with white noise. After conditioning, chicks showed no preference for spending time in the side associated with the food call or the sounds of other chicks; however, they entered a compartment first more often when it was associated with the food call and less often when it was associated with chick-sounds. Overall, these results showed that it was possible to use the conditioned place preference procedure to assess the effects of sounds and that the procedure has potential use for assessing other environmental stimuli.     

Food discrimination and induction of preference for artificial diets in the tobacco hornworm, Manduca sexta

ABSTRACT. Feeding discrimination of Manduca larvae reared on leaves and a variety of artificial media was tested against leaves, various media, solvent fractions of leaves and media, and media components, including pure chemicals. Field-collected animals showed the same preferences as did animals cultured in the laboratory for many generations. Rearing larvae on a leaf species, an artificial diet, or homogenized leaves added to artificial diet induced a preference for that food in subsequent choice tests. Extracts of these foods using organic solvents (particularly hexane) elicited feeding choices resembling those evoked by the foods themselves: water extracts were effective as stimulants or deterrents, but responses to them differed considerably from responses to the foods. Animals raised on a defined artificial diet showed an increased preference (or decreased deterrence) for the lipid component (linolenic acid) of that diet in behavioural tests. Thus induction of preference was shown to be influenced by a specific nutrient compound. Fifteen artificial diets were tested; three were successful, including a completely defined medium. Various components of the diets were tested for feeding preferences, both as omissions from the main diet and as pure compounds. Some were stimulatory, most were neutral or slightly deterrent; a few were strongly deterrent. With the exception of linolenic acid, preferences for pure compounds were not significantly correlated with the food on which the animals were reared. The data suggest that food discrimination depends on the perception of a complex chemical message comprised of both polar and non-polar compounds, with the latter being of somewhat greater importance. The results are consistent with the explanation of the induction of feeding preferences being due to a reduced responsiveness to deterrents, to an increased preference for feeding stimulants or to both.     

Predispositions and preferences. Effects on imprinting of lesions to the chick brain

Domestic chicks were exposed to a moving, stuffed jungle fowl or a rotating red box. The effects on the imprinting process of lesions to a restricted part of the hyperstriatum ventrale (IMHV) were studied in a series of experiments. Sham-operated control chicks developed a strong preference for the training object. Damage to IMHV impaired chicks' preferences for the training stimulus. However, the effect on chicks exposed to the red box was profound, whereas the effect on chicks exposed to the jungle fowl was relatively weak. The results suggest that information about a complex object, which in the experiments described resembled the chicks' own species, is stored in a different way from information derived from a relatively simple artificial object.     

A gene involved in the food preferences of larval Drosophila melanogaster

To examine the mechanism by which insects change their food preferences, a simple method was developed to measure their preferences. By using this method, we demonstrated preference of Drosophila melanogaster larvae of the yw control strain for a food based on soybeans over one based on cornmeal. We then screened for mutant strains with food preferences clearly different from the control yw strain, using the Gene Search collection of P-element insertions (GS strains). Among 380 GS strains screened using an assay plate-containing soybean and corn tastants, we identified one mutant, GS1189 that did not show any preference for either of the foods. Further behavioral assays indicated that the GS1189 larvae could have impaired olfactory and gustatory systems. The fact that the CG33071 gene expression was inactivated by the P-element insertion in the GS1189 strain, and that reversion of this gene completely recovered the normal food preference, indicates that this gene contributes to the control of food preferences in Drosophila larvae.     

Parental preference for red mouth of chicks in a songbird

Parental preferences during feeding and care-giving may select for ornamental traits in young, such as bright coloration. For chicks of coots, there is experimental evidence for this idea. We examined the hypothesis that bright yellow, orange and red mouths of chicks of songbirds have been favoured by feeding preferences in parents. In a field experiment, the orange–yellow mouths of great tit nestlings were dyed brightly red, and the feeding response of parents recorded. In nest boxes with extra daylight through a window, experimental chicks were on average given twice as much food (biomass) as control chicks (sham dyed). In normal nest boxes, the tendency was similar, but not significant. Thus, at least in good light, great tit parents prefer to feed young with red mouths, a preference for colourfulness that helps explain the evolution of bright gapes in chicks of songbirds (passerine birds).     

Sight or scent: lemur sensory reliance in detecting food quality varies with feeding ecology

Visual and olfactory cues provide important information to foragers, yet we know little about species differences in sensory reliance during food selection. In a series of experimental foraging studies, we examined the relative reliance on vision versus olfaction in three diurnal, primate species with diverse feeding ecologies, including folivorous Coquerel's sifakas (Propithecus coquereli), frugivorous ruffed lemurs (Varecia variegata spp), and generalist ring-tailed lemurs (Lemur catta). We used animals with known color-vision status and foods for which different maturation stages (and hence quality) produce distinct visual and olfactory cues (the latter determined chemically). We first showed that lemurs preferentially selected high-quality foods over low-quality foods when visual and olfactory cues were simultaneously available for both food types. Next, using a novel apparatus in a series of discrimination trials, we either manipulated food quality (while holding sensory cues constant) or manipulated sensory cues (while holding food quality constant). Among our study subjects that showed relatively strong preferences for high-quality foods, folivores required both sensory cues combined to reliably identify their preferred foods, whereas generalists could identify their preferred foods using either cue alone, and frugivores could identify their preferred foods using olfactory, but not visual, cues alone. Moreover, when only high-quality foods were available, folivores and generalists used visual rather than olfactory cues to select food, whereas frugivores used both cue types equally. Lastly, individuals in all three of the study species predominantly relied on sight when choosing between low-quality foods, but species differed in the strength of their sensory biases. Our results generally emphasize visual over olfactory reliance in foraging lemurs, but we suggest that the relative sensory reliance of animals may vary with their feeding ecology.     

An Easy Method to Test Odour Recognition in Songbird Hatchlings

We describe an easy method to test odour detection and recognition in 1‐d‐old zebra finch hatchlings (Taeniopygia guttata). Day‐old chicks beg in a stereotypical posture, which can be induced by directing gentle puffs of air from a plastic wash bottle near the face. We used this method to experimentally test whether begging duration of chicks was indicative of nest odour recognition. We manipulated the olfactory environment of 12 nests throughout incubation and hatching with either an artificial odour (orange oil) or with a neutral control (tap water). We then presented these two stimulus odours to 25 day‐old chicks and measured the duration of the first begging bout exhibited for each odour. Zebra finches hatched in a nest environment enriched with orange oil scent begged significantly longer when exposed to orange oil odour, compared to control hatchlings. Our simple testing procedure can be used to efficiently quantify odour recognition and/or preference in altricial songbirds at a very early developmental stage.     

Getting better all the time: improving preference scores reflect increases in the strength of filial imprinting

In the investigation of the neural mechanisms of filial imprinting, neurochemical measures are often correlated with preference score (PS): approach activity to the training stimulus/total approach in a test. In a previous study, domestic chicks, Gallus gallus domesticus, that had a PS under 65% were classed as 'poor learners' and those with a PS greater than 65% were called 'good learners'. We tested the effects of continued imprinting training in chicks from these two categories. After exposure to an imprinting stimulus for 30 min on day 1 after hatching, preferences were tested and then the chicks were exposed to the same stimulus for either 90 min, 3 h or 4 h on the next day, followed by a second preference test. In all these experiments there was a significant improvement in mean PS in the 'poor learners' between the first and second test, such that these chicks acquired a significant mean preference for the training stimulus. There was no such improvement in chicks that did not receive further training on day 2. When absolute approach was analysed, there was no significant difference between 'poor learners' and 'good learners' at the second test, after 4 h of retraining. Overall, mean preference scores increased with length of training. These results suggest that 'poor learners' are better characterized as 'slow learners', and that their initially low PS is not caused by, for example, a lack of motivation to express a preference. Preference scores reflect the strength of learning during imprinting. Copyright 2000 The Association for the Study of Animal Behaviour.     

Mineral metabolism in the developing turkey embryo--I. The effects of developmental age and shell-less culture on trace element contents of selected tissues.

1. Turkey embryos were incubated in ovo or in long-term shell-less culture (ex ovo) for 14, 18, 22 or 26 days. The embryos incubated ex ovo exhibited a progressive decline in the rate of growth and were hypocalcemic and hypoproteinemic compared to their in ovo counterparts from day 18 to day 26 of incubation. 2. The ratio of the concentrations of alpha-fetoprotein and albumin (AFP/A) in serum was determined for both groups of embryos. The AFP/A ratio may be useful as a biochemical index to stage avian embryonic development. Using this index it was concluded that ex ovo embryos exhibited a progressive developmental retardation compared to in ovo embryos. 3. Significant differences were observed in serum trace element concentrations for embryos incubated in ovo vs ex ovo. Most notably, serum copper concentration was significantly lower in ex ovo embryos on days 18 and 22 of incubation and significantly higher on day 26 of incubation compared to serum from embryos incubated in ovo. 4. Livers from embryos incubated ex ovo exhibited significant differences trace element levels compared to those incubated in ovo. By day 26 of incubation the concentration and total amount of zinc and iron were markedly elevated, whereas copper was greatly reduced in the livers of embryos incubated ex ovo compared to the corresponding in ovo levels. 5. Hearts from embryos incubated ex ovo contained less zinc and copper and more iron by day 26 of incubation than those from embryos incubated in ovo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Moderate Heat Challenge Increased Yolk Steroid Hormones and Shaped Offspring Growth and Behavior in Chickens

Background

Environmental challenges might affect the maternal organism and indirectly affect the later ontogeny of the progeny. We investigated the cross-generation impact of a moderate heat challenge in chickens. We hypothesized that a warm temperature–within the thermotolerance range- would affect the hormonal environment provided to embryos by mothers, and in turn, affect the morphology and behavioral phenotype of offspring.

Methodology/Principal Findings

Laying hens were raised under a standard thermal condition at 21°C (controls) or 30°C (experimental) for 5 consecutive weeks. A significant increase was observed in the internal temperature of hens exposed to the warm treatment; however plasma corticosterone levels remained unaffected. The laying rate was not affected, but experimental hens laid lighter eggs than the controls during the treatment. As expected, the maternal thermal environment affected yolk hormone contents. Eggs laid by the experimental hens showed significantly higher concentrations of yolk progesterone, testosterone, and estradiol. All chicks were raised under standard thermal conditions. The quality of hatchlings, growth, feeding behavior and emotional reactivity of chicks were analyzed. Offspring of experimental hens (C30 chicks) were lighter but obtained better morphological quality scores at hatching than the controls (C21 chicks). C30 chicks expressed lesser distress calls when exposed to a novel food. Unlike C21 chicks, C30 chicks expressed no preference for energetic food.

Conclusion/Significance

Our findings suggest that moderate heat challenge triggers maternal effects and modulate the developmental trajectory of offspring in a way that may be adaptive. This suggests that the impact of heat challenges on captive or wild populations might have a cross-generation effect.     

Food-attraction conditioning in the snail,Helix pomatia

Adult pulmonate snails (Helix pomatia) were released equidistant between two types of food, carrot and potato, respectively. Naive snails moved in different directions and did not locate either food above chance, although both foods were readily eaten upon direct contact. After a single carrot feeding episode, 75% of the carrot-fed snails moved directly towards the carrot and ate it. Conversely, potato-fed snails located the potato in 67% of the cases. Snails that were fed apple or lettuce behaved like naive animals, with the majority of animals (75% in both cases) locating neither the carrot nor the potato.The ability of snails to locate this particular food after a single feeding episode was maintained for at least 11 days, provided that the snails were not exposed to other foods in the interim. If the animals were fed a different food (but still tested for food-finding ability to the initially conditioned food) their orientation preference decreased gradually over a period of 5 days.Although the snails' orientation is based upon olfactory cues, exposure to food odor alone is not sufficient to enable food-finding; additional feeding related stimuli are necessary.These findings indicate that Helix do not possess a predisposition for the foods tested, and further suggest that processes underlying food-finding and food selection are strongly influenced by learning experiences. The conditioning phenomenon underlying food-finding behavior has been called Food-Attraction Conditioning, and appears to be a crucial link between the ecologies of learning and foraging behaviors. The accessibility of the snail's nervous system should permit neuronal analysis of the mechanisms underlying such a unique and complex learning phenomenon.     

Prenatal music stimulation facilitates the postnatal functional development of the auditory as well as visual system in chicks (Gallus domesticus)

Rhythmic sound or music is known to improve cognition in animals and humans. We wanted to evaluate the effects of prenatal repetitive music stimulation on the remodelling of the auditory cortex and visual Wulst in chicks. Fertilized eggs (0 day) of white leghorn chicken (Gallus domesticus) during incubation were exposed either to music or no sound from embryonic day 10 until hatching. Auditory and visual perceptual learning and synaptic plasticity, as evident by synaptophysin and PSD-95 expression, were done at posthatch days (PH) 1, 2 and 3. The number of responders was significantly higher in the music stimulated group as compared to controls at PH1 in both auditory and visual preference tests. The stimulated chicks took significantly lesser time to enter and spent more time in the maternal area in both preference tests. A significantly higher expression of synaptophysin and PSD-95 was observed in the stimulated group in comparison to control at PH1-3 both in the auditory cortex and visual Wulst. A significant inter-hemispheric and gender-based difference in expression was also found in all groups. These results suggest facilitation of postnatal perceptual behaviour and synaptic plasticity in both auditory and visual systems following prenatal stimulation with complex rhythmic music.