Maternal experience influences the establishment of visual/auditory, but not olfactory recognition of the newborn lamb by ewes at parturition

The Role of Oxytocin in Domestic Animal’s Maternal Care: Parturition, Bonding, and Lactation

Oxytocin (OXT) is one of the essential hormones in the birth process; however, estradiol, prolactin, cortisol, relaxin, connexin, and prostaglandin are also present. In addition to parturition, the functions in which OXT is also involved in mammals include the induction of maternal behavior, including imprinting and maternal care, social cognition, and affiliative behavior, which can affect allo-parental care. The present article aimed to analyze the role of OXT and the neurophysiologic regulation of this hormone during parturition, how it can promote or impair maternal behavior and bonding, and its importance in lactation in domestic animals.

Toward assessing the role of dietary fatty acids in lamb's neurological and cognitive development

Understanding and measuring sheep cognition and behavior can provide us with measures to safeguard the welfare of these animals in production systems. Optimal neurological and cognitive development of lambs is important to equip individuals with the ability to better cope with environmental stressors. However, this development can be affected by nutrition with a special role from long-chain fatty acid supply from the dam to the fetus or in lamb's early life. Neurological development in lambs takes place primarily during the first two trimesters of gestation. Through late fetal and early postnatal life, the lamb brain has a high level of cholesterol synthesis. This rate declines rapidly at weaning and remains low throughout adulthood. The main polyunsaturated fatty acids (PUFA) in the brain are ω-6 arachidonic acid and ω-3 docosahexaenoic acid (DHA), which are elements of plasma membranes' phospholipids in neuronal cells. DHA is essential for keeping membrane integrity and is vital for normal development of the central nervous system (CNS), and its insufficiency can damage cerebral functions and the development of cognitive capacities. In sheep, there is evidence that supplying PUFA during gestation or after birth may be beneficial to lamb productive performance and expression of species-specific behaviors. The objective of this perspective is to discuss concepts of ruminant behavior and nutrition and reflect on future research directions that could help to improve our knowledge on how dietary fatty acids (FA) relate to optimal neurological and cognitive development in sheep.

The Onset of Maternal Behavior in Sheep and Goats: Endocrine, Sensory, Neural, and Experiential Mechanisms

In sheep and goats, the onset of maternal behavior at parturition is characterized by a first phase called maternal responsiveness during which the mother is attracted to any newborn. In a second phase, called maternal selectivity, the mother establishes a selective bond with her young so that she only accepts it at suckling. After a description of the behavioral expression of both phases, this chapter reviews the physiological, sensory, and neural mechanisms involved. These two behavioral processes are synchronized with parturition by the vaginocervical stimulation induced by the expulsion of the newborn. Olfactory cues provided by the neonate are involved in maternal responsiveness and selectivity. Oxytocin supported by estrogens is the key factor for maternal responsiveness. The neural network involved in maternal responsiveness is mainly hypothalamic and is different from the circuitry involved in selectivity, which mainly concerns olfactory processing regions. Visual and auditory cues are necessary for offspring recognition at a distance. This multisensory recognition suggests that mothers form a mental image of their young. Maternal experience renders mothers more responsive to maternally relevant physiology and to young-related sensory inputs.

Maternal reactivity of ewes at lambing is genetically linked to their behavioural reactivity in an arena test

In sheep, the bond between the dam and her lambs is established during the first hours of a lamb's life. Genetic variability for behavioural reactivity of ewes assessed in an arena test performed 24 hr after lambing has already been reported. However, there is no evidence that this reactivity represents the ewe's maternal reactivity at lambing in outdoor conditions. The objective of this study was to investigate whether or not the behavioural reactivity of ewes in the arena test is genetically related to their maternal reactivity measured at lambing. A total of 935 Romane ewes were studied. The maternal reactivity of ewes at the outdoor lambing site was recorded in response to a human approach and to the handling of the lambs. Their behavioural reactivity was also recorded 24 hr post-lambing in the arena test that involved a separation from the litter and a human presence. Flight distance, aggressive reaction, time to restore contact with the litter, maternal behaviour scores and vocalizations recorded at the lambing site were heritable (0.12-0.34). All of these behaviours were genetically correlated with the behavioural reactivity in the arena test. The highest genetic correlations (from 0.60 to 0.90) were found amongst maternal behavioural scores, flight distance and high-pitched bleats. In conclusion, behavioural reactivity in the arena test can be used to assess early maternal reactivity in standardized conditions. Phenotyping of ewes' behavioural reactivity with a simplified arena test can be performed for genetic improvement in maternal behaviour in sheep.

Neurophysiological Mechanisms of Mother-Young Bonding in Buffalo and Other Farm Animals

Simple Summary

The present paper reviews the importance of bonding for the survival and well-being in the cow–calf relationship. The review focuses on buffaloes and information from other species is used for comparison or to find more general patterns in the absence of specific sources. Differences between several farm species are also described, focusing on the role played by the sensory stimuli during the sensitive period after birth. How bonding can be classified according to the predominant senses used by different species, the importance of learning (i.e., imprinting) in the development of mother–young relationship, and the neurobiological mechanisms involved are also delineated. Finally, some examples of the main factors that can affect the mother–young relationship in the field are given. By understanding the imprinting at brain level, as well as the relationship with behavior, we gain a deeper insight into the critical role that experience, and environmental factors play in shaping the development of the mother–offspring bond.

Abstract

In buffaloes and other mammalian farm species, the mother provides food and protection to the young, but she is also the main source of behavioral and social learning for the offspring. It is important that mother and young establish a bond based on a learning mechanism defined as “imprinting” early after parturition during the sensitive period, on which the welfare and survival of the offspring will depend. This review aims to summarize and discuss current knowledge regarding the imprinting process, the neurobiological pathways that are triggered during this sensitive period, and the development of the cow–calf bond. Touch, hearing, vision, and smell seem to be the predominant senses involved during imprinting in buffaloes and other mammalian farm species. In buffalo, bonding is very particular due to the expression of specific behaviors, such as allo-suckling and communal rearing. In general, imprinting and the subsequent bond may be affected by the lack of experience of the mothers or dystocic parturitions, which occur most frequently with male calves and in primiparous dams. The main problems in the development of this process include lack of seeking a protected and isolated place to give birth; moving from the birth-site after parturition; insufficient postpartum care; aversion or aggressiveness towards the newborn, or abandonment of the newborn. The process can develop differently according to the species. However, the correct development of the cow–calf relationship represents, regardless of the species, a key factor for their fitness.

Ewe-lamb bond of experienced and inexperienced mothers undernourished during gestation

The aims were to compare ewe-lamb behaviours between primiparous (PRI) and multiparous (MUL) undernourished grazing ewes at birth and at 3 months of age, and to determine if mothers’ parity affects milk yield and composition, and lambs’ body weight (BW). Food availability restricted the nutritional requirements from day 30 to day 143 of gestation. The MUL ewes had greater BW than the PRI during gestation, and their lambs tended to vocalize less frequently until their first suckle. PRI ewes both displayed a lower frequency of acceptance behaviours and, a greater number of high-pitched bleats toward the alien lamb than toward that of their own, but MUL did not. PRI ewes produced less milk than the MUL ewes. The heart rate was greater in lambs reared by MUL ewes than by PRI. Although PRI ewes had a lower BW during gestation, this difference was stable throughout and did not affect the establishment of the ewe-lamb bond neither at birth nor at 3 months postpartum. At least under nutritionally restricted conditions during gestation, inexperienced mothers appeared to have had a shorter sensitivity period of maternal responsiveness than that of experienced mothers.

Genetic parameters estimates for ewes' behavioural reactivity towards their litter after lambing

In livestock, improving maternal reactivity towards the litter is an important issue in breeding strategies to promote production and animal welfare. As of yet, no studies have investigated the within-breed genetic variation of maternal reactivity in sheep. The objective of this study was to estimate the genetic parameters of maternal reactivity traits. A total of 1,095 primiparous and 1,441 multiparous Romane ewes were phenotyped 24 hr postlambing using a behavioural test (arena test, AT) over a 10-year experimental period. The test consisted of three successive phases evaluating the ewe's attraction to her litter, reactivity to separation from her litter, and reactivity to a conflict between attraction to her litter and avoidance of a motionless human. The ewes were reared exclusively on rangelands (South of France) and lambed outdoors in the spring. High-pitched bleating and low-pitched bleating in the AT were mostly highly heritable (0.39-0.46). Heritabilities were moderate for proximity to the litter in the presence of a human (0.27) and low for locomotion and vigilance in the AT (0.09-0.15). The measurements of a given behaviour in the three phases of the AT were highly genetically correlated. Few genetic correlations were found between the different behavioural traits in the AT, the highest correlations being between high-pitched bleating and low-pitched bleating (-0.43 to -0.77). In conclusion, our findings demonstrate moderate-to-high heritability for maternal reactivity traits. These traits could be included in genetic selection schemes to enhance maternal attachment provided there is no unfavourable link with other production traits.

The parental brain and behavior: A target for endocrine disruption

During pregnancy, the sequential release of progesterone, 17β-estradiol, prolactin, oxytocin and placental lactogens reorganize the female brain. Brain structures such as the medial preoptic area, the bed nucleus of the stria terminalis and the motivation network including the ventral tegmental area and the nucleus accumbens are reorganized by this specific hormonal schedule such that the future mother will be ready to provide appropriate care for her offspring right at parturition. Any disruption to this hormone pattern, notably by exposures to endocrine disrupting chemicals (EDC), is therefore likely to affect the maternal brain and result in maladaptive maternal behavior. Development effects of EDCs have been the focus of intense study, but relatively little is known about how the maternal brain and behavior are affected by EDCs. We encourage further research to better understand how the physiological hormone sequence prepares the mother's brain and how EDC exposure could disturb this reorganization.

Female-female aggression in goitered gazelles: the desire for isolation

In contrast to males, which compete with other males for access to mates, females compete with each other for forage-rich sites, birthing grounds, comfortable resting places, and access to sources of water and salt licking locations. This behavior has been observed in many species. However, many agonistic interactions between females occur where resources are not immediately at stake, and the reasons for their rivalry are often unclear. Therefore in this paper, I want to analyze the main causes of female-female aggression in the yearly cycle of goitered gazelles. I found that adult females had conflicts moistly with sub-adult females and less with other adult females; and these behaviors were observed mainly in May, with less in June, and only a few cases displayed during the rest of the year. The months of May-June had the most abundant and highest quality forage of the year, when competition for resources would seem to be least expected. Struggles for resting places occurred throughout the entire year, with only some bias for May that did not represent a primary level of aggression. In reality, the high rate of female-female aggressive interactions was related to the protection of birthing grounds, where mothers isolated themselves to give births, establish a strong selective mother-young bonds, keep their hiding fawns separated from alien offspring (having initial problems with distant visual recognition), and protect them against disturbance from all other females, which can undermine a fawn's hidden status and make it more vulnerable to predation.

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Flawed mothering or infant signaling? The effects of deficient acoustic cues on ovine maternal response

The neonate distress cry, which displays a similar acoustic structure across a range of mammalian species, is highly effective in attracting, even compelling, parental care. However, if this cry is defective, as found in human and rodent neonates with poor neurobehavioral function, is the signal less enticing? Using playback recordings of a ewe's own co-twins as stimuli in a two choice test, we compared the preference of each sheep dam for acoustic features of lamb distress calls to assess the impact of signal quality on maternal response. The results of this study indicate that lamb vocalizations with acoustic parameters reflecting poor vocal fold engagement and arousal were less likely to be preferred by their dam. Additionally, these calls were associated with delayed vocal initiation and poor infant survival behavior suggestive of subtle cognitive deficit; and support the possibility that, as in deer and rodents, ovine vocalizations within a specific fundamental frequency range may well be a trigger for optimal maternal behavior. This research has important implications for understanding failed maternal-young interactions in ungulate and other species, and for verifying standardization of infant stimuli used in maternal behavior studies.

Mother-young recognition in goitered gazelle during hiding period

The mother-young recognition process is crucial for the growth and survival of progeny. In "follower" ungulate species, vocal and visual cues have been found to play a leading role in the mother-young identification process from the first days postpartum, with olfactory cues also important in establishing the initial selective mother-young bond immediately after birth. In "hider" species, however, much less has been documented of mother-young recognition behaviors, especially in their natural habitat. In this paper, we investigated this process in goitered gazelle (Gazella subgutturosa), a typical hider species, in its native environment in Kazakhstan. Over the course of our study period, we investigated the behaviors of 257 females with twins and 158 females with singles through visual observations. We found that within the first month after birth, when females spend only a short time with their young, mothers recognized their fawns using mostly olfactory cues, while vision was used to locate their hiding offspring. Fawns vocalized very rarely, producing only distress calls that did not seem intended for individual identification. Licking of young by their mothers was observed frequently, not only during the first week after birth, when this action was very important for fawn stimulation for a number of physiological functions, but for several weeks after (until one month of age), when licking lost its physiological importance and likely became more of a recognition procedure. Fawns did not recognize their mothers at all, either through vision or vocalizations, since during their first weeks after birth, they responded to any gazelle that approached their hiding area. By a month after birth, when mothers and fawns began to stay together for longer periods of time, their recognition process became more enhanced, and in addition to olfactory cues, the mother and her young began to use more and more visual cues for longer distance identification, as well as vocalizations for shorter distances. Similar dynamics are likely typical for most hiding species, although information for wild ungulates is still very limited, especially for those with strong hider behaviors.

Survival of lambs from maiden ewes may not be improved by pre-lambing exposure to mature lambing ewes

The survival of lambs born to ewes at their first (maiden) lambing is generally lower than for those born to ewes which have previously lambed, and poor maternal behaviour is a contributing factor. This study examined whether pre-lambing exposure of maiden ewes to multiparous lambing ewes would improve the survival of lambs born to maiden ewes. Pregnant maiden (n = 333, 2 years of age) Merino ewes were allocated to three replicates of two treatments: exposed – maidens were grazed with multiparous Merino ewes (n = 111, 5 or 7 years of age), which were due to lamb during the 2 weeks before the start of maiden lambing, with mature ewes comprising 50% of the mob size; and non-exposed – maiden ewes grazed in paddocks without mature ewes. The total number of ewes per paddock (74), number of ewes per hectare (14.0) and paddock size were the same in both treatments. The number of lambs born per ewe was similar between treatments, indicating a similar proportion of multiple births. The proportion survival of lambs from maiden ewes exposed to adults (0.53) tended to be lower (P = 0.091) than the survival of lambs born to maiden ewes grazing alone (0.61). The number of lambs marked per ewe lambing was similar (P = 0.284) in exposed (0.71) compared with non-exposed (0.78) maidens. The survival of lambs from maiden ewes was not improved by lambing in the same paddock with adults, even where the adults had largely completed lambing before the maidens commenced.

Chemical olfactory signals and parenthood in mammals

This article is part of a Special Issue "Chemosignals and Reproduction". In mammalian species, odor cues emitted by the newborn are essential to establish maternal behavior at parturition and coordinate early mother-infant interactions. Offspring odors become potent attractive stimuli at parturition promoting the contact with the young to ensure that normal maternal care develops. In some species odors provide a basis for individual recognition of the offspring and highly specialized neural mechanisms for learning the infant signals have evolved. Both the main and the accessory olfactory systems are involved in the onset of maternal care, but only the former contributes to individual odor discrimination of the young. Electrophysiological and neurochemical changes occur in the main olfactory bulb leading to a coding of the olfactory signature of the familiar young. Olfactory neurogenesis could also contribute to motherhood and associated learning. Parturition and interactions with the young influence neurogenesis and some evidence indicates a functional link between olfactory neurogenesis and maternal behavior. Although a simple compound has been found which regulates anogenital licking in the rat, studies identifying the chemical nature of these odors are lacking. Neonatal body odors seem to be particularly salient to human mothers who are able to identify their infant's odors. Recent studies have revealed some neural processing of these cues confirming the importance of mother-young chemical communication in our own species.

The power of oral and nasal calls to discriminate individual mothers and offspring in red deer, Cervus elaphus

BACKGROUND

In most species, acoustical cues are crucial for mother-offspring recognition. Studies of a few species of ungulates showed that potential for individual recognition may differ between nasal and oral contact calls.

RESULTS

Vocalizations of 28 hinds and 31 calves of farmed Iberian red deer (Cervus elaphus hispanicus) were examined with discriminant function analyses (DFA) to determine whether acoustic structure of their oral and nasal contact calls encodes information about the caller's identity. Contact calls were elicited by brief separation of individually identified animals by a distance over 10 m or by a bar fence. Both oral and nasal calls of both hinds and calves showed high potential to discriminate individuals. In hinds, individuality was significantly higher in the oral than in the nasal calls, whereas in calves, individuality was equally well expressed in both oral and nasal calls. For calves, the maximum fundamental frequency was higher and the duration was longer in oral calls than in nasal calls. For hinds, the maximum fundamental frequency and the duration were indistinguishable between oral and nasal calls. Compared to the pooled sample of oral and nasal calls, separate oral or nasal call samples provided better classifying accuracy to individual in either hinds or calves. Nevertheless, in both hinds and calves, even in the pooled sample of oral and nasal calls, the degree of individual identity was 2-3 times greater than expected by chance. For hinds that provided calls in both years, cross-validation of calls collected in 2012 with discriminant functions created with calls from 2011 showed a strong decrease of classifying accuracy to individual.

CONCLUSIONS

These results suggest different potentials of nasal and oral calls to allow the discrimination of individuals among hinds, but not among red deer calves. The high potential of individual recognition even with the pooled sample of oral and nasal calls allows mother and young to remember only one set of acoustic variables for mutual vocal recognition. Poor between-year stability of individual characteristics of hind oral and nasal calls would require updating keys to individual recognition each calving season.

Storing maternal memories: hypothesizing an interaction of experience and estrogen on sensory cortical plasticity to learn infant cues

Much of the literature on maternal behavior has focused on the role of infant experience and hormones in a canonical subcortical circuit for maternal motivation and maternal memory. Although early studies demonstrated that the cerebral cortex also plays a significant role in maternal behaviors, little has been done to explore what that role may be. Recent work though has provided evidence that the cortex, particularly sensory cortices, contains correlates of sensory memories of infant cues, consistent with classical studies of experience-dependent sensory cortical plasticity in non-maternal paradigms. By reviewing the literature from both the maternal behavior and sensory cortical plasticity fields, focusing on the auditory modality, we hypothesize that maternal hormones (predominantly estrogen) may act to prime auditory cortical neurons for a longer-lasting neural trace of infant vocal cues, thereby facilitating recognition and discrimination. This couldthen more efficiently activate the subcortical circuit to elicit and sustain maternal behavior.

Amniotic fluid is important for the maintenance of maternal responsiveness and the establishment of maternal selectivity in sheep

Amniotic fluid (AF) is important for the establishment of maternal behaviour in inexperienced ewes, but its role in experienced mothers remains to be studied. Here, the maintenance of post-partum maternal responsiveness and the establishment of exclusive bonding was investigated in multiparous ewes when AF was removed from the neonate or/and physical contact with the young was precluded for the first 4 h post partum. Maintenance of maternal responsiveness and establishment of exclusive bonding were measured by the proportion of mothers accepting their own lamb and alien lambs that had been either washed or not washed, and by comparing an acceptance score for each type of lamb. The acceptance score was computed by summing standardised variables of acceptance (low bleats, acceptance at udder, nursing and licking time) and subtracting standardised variables of rejection (high-pitched bleats, rejection at the udder and aggressive behaviour). Washing the neonate reduced its acceptance score, but the proportion of mothers rejecting their own lamb was reduced only when washing the neonate and prevention of physical contact for 4 h were combined (7/15 v. 0/10 in controls, P = 0.02). In addition, washing the neonate increased the acceptance score of the washed alien lamb, but not of the unwashed alien. However, washing and privation of physical contact did not increase significantly the proportion of mothers accepting an alien lamb at 4 h post partum. We conclude that AF is important in experienced ewes for the establishment of maternal responsiveness, as already found in primiparous mothers. In addition, our results indicate that AF also carries some chemosensory information facilitating exclusive bonding.

Mother-young relationships in sheep: a model for a multidisciplinary approach of the study of attachment in mammals

The onset of maternal responsiveness and the development of mother-young attachment in sheep are under the combined influence of hormonal and sensory stimulations. In the mother, the prepartum rise in oestrogen and vaginocervical stimulation caused by expulsion of the foetus act on the main olfactory system and on hypothalamic regions. This induces maternal care through the central release of oxytocin, modulated by opiates and corticotrophin-releasing hormone. In parallel, activation of the main olfactory network enables the learning of individual lamb odour and maternal attachment. In the neonate, the first suckling episodes and the concomitant activation of the cholecystokinin, opioids and oxytocin systems facilitate the development of a preference for the mother. Gastrointestinal signals activate the brain stem, the hypothalamus and the amygdala. Within 72 h of parturition, the mother-young attachment shifts from proximal to distal recognition based on visual and auditory cues after which vocal cues become more salient. Although olfaction remains a key element in the display of selective maternal nursing, maternal attachment relies on a multisensory mental image of the lamb. These findings support the view that sheep are amongst the most appropriate animal models for the study of maternal and filial attachment in mammals.

Development of social familiarity in ewes

We assessed the development of individual discrimination resulting from direct contact/familiarization in ewes. Unfamiliar ewes were introduced during 6, 24 or 72 h in groups of already familiarized ewes. At the end of this contact period, the development of social recognition with the animal that has been introduced was assessed using two different types of tests: a Y-maze preference test and a delayed paired close encounters test where tested ewes are successively and randomly interacting with the familiar animal and an unfamiliar conspecific. The results of both tests showed that ewes developed a recognition of the familiar animal in comparison to a completely unfamiliar female. However, this preference was evidenced after 24 h of contact when using the paired close encounters test whereas it appears only after 72 h when using the Y-maze test, suggesting that the paired close encounters test is a more sensitive methodology to assess the development of social familiarization. The importance of estrogens, in the formation of social familiarization was also evaluated. To this end, social recognition in the paired close encounters test was compared between ovariectomized animals receiving estrogen implants or not. Despite significant high levels of estradiol in estrogen implanted females, no major differences in recognition appeared between groups, suggesting that in our conditions estrogens do not have major influence on social familiarization.

Vaginocervical stimulation of Ewes induces the rapid formation of a new bond with an alien young without interfering with a previous bond

Ewes form a selective olfactory memory for their lambs after 2 hr of mother-young interaction following parturition. Mothers will subsequently reject any strange lamb at suckling. The present study investigated whether artificial vaginocervical stimulation (VCS) allows the formation of a selective bond with an unfamiliar lamb and whether it interferes with the maintenance of the bond formed with the familiar lamb. At 2 hr postpartum, mothers were separated from their familiar lamb after having formed a selective bond with it and were given 10 min of mechanical VCS. In the "VCS + lamb" group (n = 24) an unfamiliar lamb was left with the ewe for 2 hr whereas in the "VCS no lamb" group (n = 26) the mother was left alone for the same period of time. Ewes of the "no VCS" group (n = 14) did not receive any VCS. In the majority of animals of the "VCS + lamb" group (23/24) VCS induced a complete acceptance of the unfamiliar lamb without any disruption of the bond previously formed with the familiar lamb. VCS or 2 hr of separation did not disrupt the maintenance of the selective bond initially formed with the familiar lamb since all the ewes of the "VCS no lamb" and "no VCS" groups accepted it at suckling.

Challenge by a novel object does not impair the capacity of ewes and lambs selected for a nervous temperament to display early preference for each other

Novelty, a powerful fear-inducing and stressful stimulus, could be detrimental on the capacity of ewes and lambs to recognise each other. The effect of a novel object on the ability of ewes and lambs, selected for their calm or nervous temperament, to show a preference for each other was tested in a two-choice discrimination test. Both calm and nervous temperament mothers showed a preference towards their own offspring rather than the alien lambs. Nervous temperament ewes also looked at their own lamb more than the alien. In contrast, nervous lambs showed a greater preference and took less time to reach their own mother than calm lambs. Nervous temperament does not seem to impair the capacity of ewes and lambs to display an early preference for each other, and might be an advantage in some challenging postnatal situations because of the increased motivation of nervous lambs to reunite with their mother.

Mother–young vocal communication and acoustic recognition promote preferential nursing in sheep

In mammals with precocial neonates, exclusive maternal care and investment depend on mutual mother–young recognition. In sheep, this is ensured by rapid olfactory recognition of the neonate by its mother. However, recent studies suggest that other processes may participate in preferential maternal care. We investigated the possibility that acoustic communication promotes preferential nursing of the lamb. In the first of two studies, we examined the association between nursing and vocal activity in ewes and their lambs during the first 2 weeks of lactation. As early as 3 and 6 h postpartum, vocal activity was preferentially concentrated before nursing and by day 15 all vocal activity occurred within 2.5 min before nursing. In the second study, we tested the responses of ewes and lambs at 15 days postpartum to the playback of recorded bleats of their partner or from unrelated ewes and lambs. When playback was performed 30 min after a nursing episode, both ewes and lambs responded to bleats of their partner but not to bleats from alien subjects. When playback was performed 5 min after nursing, ewes did not respond to any lamb's bleats, while lambs continued responding to the bleats of their mothers, but significantly less than 30 min after nursing. Nursing therefore appears to play an important role in structuring very early vocal communication between the mother and her neonate. In turn, if the motivational state of the members of the mother–young dyad is adequate, this ensures the display of mutual acoustic recognition and prepares them for preferential nursing before maternal olfactory recognition of the lamb comes into play.

Eyeblink classical conditioning in the preweanling lamb

Classical conditioning of eyeblink responses has been one of the most important models for studying the neurobiology of learning, with many comparative, ontogenetic, and clinical applications. The current study reports the development of procedures to conduct eyeblink conditioning in preweanling lambs and demonstrates successful conditioning using these procedures. These methods will permit application of eyeblink conditioning procedures in the analysis of functional correlates of cerebellar damage in a sheep model of fetal alcohol spectrum disorders, which has significant advantages over more common laboratory rodent models. Because sheep have been widely used for studies of pathogenesis and mechanisms of injury with many different prenatal or perinatal physiological insults, eyeblink conditioning can provide a well-studied method to assess postnatal behavioral outcomes, which heretofore have not typically been pursued with ovine models of developmental insults.

Individual variation in the expression of maternal behaviour: a review of the neuroendocrine mechanisms in the sheep

Individual variation in the expression of maternal behaviour can affect offspring development and survival. Ewes showing a poorer quality of maternal behaviour (low levels of licking and grooming, infrequent low-pitched bleating, inconsistent udder acceptance) at parturition and throughout lactation (large ewe-lamb distance, low vigilance) form a weaker bond with their lambs, and have higher lamb mortality, than ewes which show high levels of grooming and low-pitched bleating, close ewe-lamb distances and high levels of vigilance. Using two models of variation in maternal behaviour in the sheep (differences between ewes of two breeds, and differences between primiparous and multiparous ewes), the neuroendocrine mechanisms that underpin these differences are explored. In both cases, significant variation in oestrogen priming is observed, with breed differences in circulating concentrations of oestrogen in late gestation, and parity effects on receptor density but not circulating concentrations. The consequences of these differences for central oxytocin release and binding are discussed. In addition, preliminary data suggest that opioid modulation, in both breed and parity models, may also play a role in mediating individual variation in maternal behaviour in the sheep.

Genetic and physiological determinants of maternal behavior and lamb survival: Implications for low-input sheep management1,2

The relatively intensive supervision afforded many ewes at lambing time is a barrier to the development of low-input sheep management systems. However, in some flocks, reduction in this level of supervision may initially affect lamb mortality and animal welfare. In this review, possibilities for optimizing behavioral interaction between the ewe and lamb are considered, with the goal of improving lamb survival without the need for high levels of human supervision. At birth, ewes show specific behavioral patterns (e.g., licking or grooming, low-pitched bleats, udder acceptance) that facilitate the transition of the lamb from pre- to postnatal life and that accompany the formation of an exclusive olfactory memory for the lamb. The lamb also performs a specific sequence of behaviors directed toward standing, finding the udder, and sucking. The successful accomplishment of these behavior patterns is vital for the formation of a strong attachment between both partners, and for lamb survival. The expression of maternal behavior in the ewe is affected by her previous maternal experience, by nutrition in pregnancy, by breed, by temperament, and, to some extent, by the behavior of her lamb. The maternal care expressed by a ewe at parturition is indicative of her behavior throughout that lactation and in successive pregnancies, suggesting an underlying basis to maternal care intrinsic to that ewe. Studies with Scottish Blackface and Suffolk ewes show that ewes expressing high levels of maternal care have elevated plasma estradiol in late gestation compared with ewes with poorer maternal care, and that circulating estradiol concentration is correlated with maternal behaviors. Although the genetic basis of maternal behaviors has still to be fully determined, there are possibilities of improving maternal behavior by selection, and a better understanding of the neuroendocrine processes underlying individual differences in maternal behavior may help in developing selection strategies. In addition, selection on lamb behaviors, which show some genetic basis, may also be a route to improve lamb survival. Because behavior of both the ewe and lamb is affected by environmental factors, appropriate management, through pregnancy and at parturition, will enhance the expression of maternal behavior and lamb vigor, and so contribute to improving lamb survival.

Parity effects on maternal behaviour are not related to circulating oestradiol concentrations in two breeds of sheep

Primiparous females of many species, including the sheep, do not show as competent maternal behaviour as multiparous mothers. In this study we investigated whether circulating concentrations of oestradiol might be related to this response, since breed differences in oestradiol concentrations have been shown to correlate with maternal behaviours. Oestradiol concentrations were measured in plasma collected at 2-weekly intervals from primiparous and multiparous ewes of two breeds (Scottish Blackface and Suffolk) throughout gestation, and maternal behaviour was recorded at parturition. Circulating oestradiol concentrations, and the ratio of oestradiol to progesterone concentration (O:P ratio) were higher in late pregnancy in Blackface ewes, but there were no significant effects of ewe parity. However, there was a significant interaction between breed and parity as O:P ratio was lower in primiparous Suffolk ewes compared to multiparous. This relationship was not seen in Blackface ewes. Blackface ewes of both parities groomed their lambs more frequently and made more low-pitched vocalisations than Suffolk ewes. Primiparous ewes were more likely to move as the lamb attempted to suck, and to show withdrawal or aggression towards the lamb. Primiparous Suffolk ewes also made more high pitched bleats than other classes of ewe. The data support previous studies which show an effect of breed on circulating oestradiol and O:P ratio but suggest that parity effects on maternal behaviour may be mediated by sensitivity to circulating concentration of oestradiol rather than variations in the plasma concentrations of this hormone.

Establishment of vocal communication and discrimination between ewes and their lamb in the first two days after parturition

In sheep, the mother-young relationship is characterized by an exclusive bond that relies on the rapid establishment of mutual recognition. However, the role of acoustic cues has been underestimated and neglected in this early discrimination. Therefore, the aim of the present study was (1) to characterize the vocal behavior of ewes and their lambs during the first 15 days postpartum and (2) to investigate the ability of newborn lambs and their mothers to discriminate each other from alien subjects within the first 48 hr postpartum on the basis of acoustic cues only. Ewes started to vocalize in the last 3 hr preceding parturition, emitting mainly high-pitched bleats. However, the bleating activity was highest during the first 3 hr following birth, consisting mainly of low-pitched bleats. Thereafter it decreased sharply until 24 hr postpartum, with most of the activity coming from the mother. In a two-choice test, ewes discriminated their own from an alien lamb on the basis of acoustic cues only at 24 hr postpartum, while lambs did so for their mother at 48 hr, which in both cases was much earlier than reported so far. We conclude that early vocal recognition between the ewe and her lamb may play an important role for the maintenance of mother-young contact.

Perinatal visceral events and brain mechanisms involved in the development of mother-young bonding in sheep

In sheep the onset of maternal responsiveness and the development of the mutual mother-young bond are under the combined influence of hormonal and visceral somatosensory stimulations. These stimuli are provided in the mother by parturition (via steroids and vaginocervical stimulation) and in the neonate by the first suckling episodes (via cholecystokinin and oro-gastro-intestinal stimulation). In addition, each partner relies on specific chemosensory stimulation for reciprocal attraction: amniotic fluids for the mother, colostrum for the young. In the ewe parturition activates several brain structures to respond specifically to sensory cues emanating from the young. The main olfactory bulbs undergo profound neurophysiological changes when exposed to offspring odors at parturition. Additional activations in the hypothalamus - preoptic area - and the amygdala - medial and cortical nuclei - also contribute to maternal responsiveness and memorization of lamb odors. In the neonate, post-ingestive stimulations activate the brain stem via vagal afferents. Like in the ewe, several regions of the hypothalamus and the amygdala respond to colostrum ingestion suggesting common ground for the integrative neural processes involved in early learning and bonding. This leads to rapid visual and auditory recognition in both partners although olfaction remains important in the ewe to display selective nursing. It is concluded that the biological basis for the development of maternal and filial bonding in sheep presents striking similarities.

From birth to colostrum: early steps leading to lamb survival

New-born lambs have limited energy reserves and need a rapid access to colostrum to maintain homeothermy and survive. In addition to energy, colostrum provides immunoglobulins which ensure passive systemic immunity. Therefore, getting early access to the udder is essential for the neonate. The results from the literature reviewed here highlight the importance of the birth site as the location where the mutual bonding between the mother and her young takes place. Attraction to birth fluids by the periparturient ewe leads to intense licking of the lamb. Grooming not only dries, cleans and stimulates the newborn it also facilitates bonding through learning of its individual odour. Ewes having twins should ideally stay on the birth site for at least six hours in order to establish a strong bond with both lambs and favour lambs survival. However, primiparous ewes or ewes having high levels of emotivity are more likely to exhibit poor maternal behaviour. In addition, difficult parturition and weather conditions have an indirect effect on the behaviour of the mother and are other major causes of lamb death. On the lamb's side, rapid access to the udder and early suckling are extremely important. Delayed lactation or insufficient colostrum yield may be fatal especially since suckling has strong rewarding properties in the establishment of a preference for the mother, which in turn increases lamb survival. Insufficient access to the udder in mothers leaving the birth site too soon after parturition, especially in twin-bearing ewes, could also partly account for the high incidence of loss of mother-young contact and subsequent death in such lambs. Strategies to improve neonatal survival should be aimed at maximising lamb vigour, colostrum production, and mutual mother-young bonding through adequate feeding in late pregnancy and selection on behaviour.

Maternal responsiveness and maternal selectivity in domestic sheep and goats: The two facets of maternal attachment

Sheep and goats rapidly establish an exclusive relationship with their neonate following contact with it during a sensitive period of maternal responsiveness induced by the physiological events occurring at parturition. The data concerning the sensory, physiological, and neurobiological factors involved in the activation of both maternal responsiveness and the establishment of selective nursing indicates that these processes are activated simultaneously by the combined action of two main factors, the prepartum rise in circulating estrogen and the vaginocervical stimulation (VCS) caused by fetus expulsion. On the one hand, these two factors act on a neural network including the main olfactory system (MOB), the medial preoptic area (MPOA), and the paraventricular nucleus of the hypothalamus (PVN) to induce maternal responsiveness towards any neonate. The intracerebral release of oxytocin (OT) from the PVN, and the triggering of olfactory attraction for amniotic fluid (AF) are key elements in this process. On the other hand, VCS at birth also sets the MOB ready to memorize the individual odor of the neonate, through the release of peptides and neurotransmitters (noradrenaline and acetylcholine). In addition to the MOB, the network involved in recognition mainly includes the medial and cortical amygdala. Across consolidation processes, reorganization occurs in the network engaged in lamb recognition. Whether this memorization may be potentiated by other sensory cues is not known. The identification of the chemosensory compounds involved in the attraction for AF and in the recognition of the neonate is important for understanding the mechanisms of maternal attachment.