Maternal Behaviour In Sheep Research Articles

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 24hr 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 24hr 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.

Disruption of adult olfactory neurogenesis induces deficits in maternal behavior in sheep

Profound behavioral changes occur in the mother at parturition, a time when the maternal brain undergoes extensive remodeling of neural circuits, especially in olfactory structures. Adult neurogenesis, a form of brain plasticity, could constitute an adaptive response to motherhood. The present study hypothesized that chemical disruption of olfactory neurogenesis would impair the establishment of maternal behavior in sheep. In addition, because ewes are able to learn the olfactory signature of their offspring, we also examined whether disruption of olfactory neurogenesis altered recognition of the familiar lamb. At one month of gestation, ewes received either infusion of the antimitotic drug Ara-C or saline into the lateral ventricles via one-month-long osmotic minipumps. Ara-C infusion dramatically decreased olfactory neurogenesis but spared hippocampal neurogenesis. Mothers exhibiting more than a 70% reduction in olfactory neurogenesis emitted fewer maternal bleats during the first hours after parturition. Reduction of olfactory neurogenesis also negatively affected discrimination of the familiar lamb. Differences in ewes’ aggressive behavior toward familiar and alien lambs were observed in sham mothers, but not in mothers with reduced olfactory neurogenesis. In addition, when ewes were given the choice between familiar and unfamiliar anesthetized lambs, so that only olfactory cues were available, mothers with a reduction in neurogenesis greater than 70% were not able to discriminate their own lamb from an alien lamb. These results indicate that adult-born olfactory neurons are to some extent involved in the establishment of maternal behavior in sheep by contributing to the processing of offspring odors.

Identification of SNPs within the PRLR gene and effects on maternal behavior in sheep.

The prolactin receptor gene (PRLR) plays an essential role in maternal behavior. The aim of the study was to detect PRLR mutations in exon 10, using a polymerase chain reaction-single stranded conformation polymorphism method, and to determine the association between mutations in this region with maternal behavior traits in Chinese Hu sheep. Polymorphisms were detected only in the gene region amplified by the primer P3; three genotypes (AA, AB and BB) were observed. The genotype BB was predominant in the ewe study population, and genotype distributions were in agreement with the Hardy-Weinberg equilibrium (P > 0.05). There was no significant difference between observations for licking and kicking behaviors of AA and AB genotype individuals (P > 0.05), but there was a significant difference (0.01 < P ≤ 0.05), when both were compared with the BB genotype. Significant differences were observed in suckling behavior between AA and AB genotype individuals (0.01 < P ≤ 0.05), and the difference between these two genotypes and BB was highly significant (P ≤ 0.01). No obvious difference was observed between the genotypes in behavior of suckling rejection (P > 0.05). These results contribute to methods for selection and breeding through marker-assisted selection for maternal behavior traits in Hu sheep.

Pen size and parity effects on maternal behaviour of Small-Tail Han sheep

The aim of this experiment was to study the effects of pen size and parity on maternal behaviour of twin-bearing Small-Tail Han ewes. A total of 24 ewes were allocated to a 2×2 design (six per pen), with parity (primiparous or multiparous) and pen size (large: 6.0×3.0 m; small: 6.0×1.5 m) as main effects at Linyi University, Shandong Province, China. Behaviour was observed from after parturition until weaning. All ewes were observed for 6 h every 5 days from 0700 to1000 h and from 1400 to 1700 h. Continuous focal animal sampling was used to quantify the duration of maternal behaviours: sucking, grooming and following as well as the frequency of udder accepting, udder refusing and low-pitched bleating. Oestradiol and cortisol concentrations in the faeces (collected in the morning every 5 days) were detected using EIA kits. All lambs were weighed 24 h after parturition and again at weaning at 35 days of age. The small pen size significantly reduced following (P<0.005), grooming (P<0.001) and suckling durations (P<0.05), as well as the frequency of udder refusals (P<0.001). However, there was a significant interaction with ewe parity, with decreased grooming and suckling in the small pen largely seen in the multiparous ewes (P<0.001). Independent of pen size, multiparous ewes accepted more sucking attempts by their lambs (P<0.05) and made more low-pitched bleats than primiparous ewes (P<0.001). Multiparous ewes had higher faecal oestradiol concentrations than primiparous ewes (P<0.001), and ewes in small pens had higher faecal cortisol levels compared with ewes in larger pens (P<0.001). As lambs increased in age, the duration of maternal grooming, following and suckling as well as frequency of udder acceptance and low-pitched bleating all declined, and the frequency of udder refusing increased (P<0.001 for all). Ewe parity, but not pen size, affected lamb weight gain during the period of observation (P<0.001). This is the first study to show that pen size, interacting with parity, can affect the expression of maternal behaviour in sheep during lactation. The study is also the first to report on the maternal behaviour of Chinese native sheep breeds (Small-Tail Han sheep), with implications for the production of sheep in China.

Maternal behaviour and peripartum levels of oestradiol and progesterone show little difference in Merino ewes selected for calm or nervous temperament under indoor housing conditions

Temperament influences the expression of maternal behaviour in sheep under experimental field conditions. We investigated whether maternal behaviour between ewes selected for a calm or nervous temperament is independent from environmental conditions. In addition, the level of maternal behaviour expressed by mothers is correlated with the concentration of hormones during the peripartum period. Therefore, we investigated whether the selection for temperament had resulted in hormonal differences between the two lines with regard to the hormones that could be involved in the onset of maternal behaviour. Oestradiol, progesterone and cortisol concentrations from 4 days before parturition to 24 h after parturition were determined from blood samples collected from 10 calm and 12 nervous ewes. Behavioural interactions between ewe and lamb were also recorded for 2 h starting at parturition. Mothers of both temperament lines showed adequate maternal behaviour under the controlled conditions of the study. Therefore, the results of the study do not suggest that selection for a calm or nervous temperament has profoundly affected the intrinsic ability of mothers to display adequate maternal behaviour. Hormonal differences between the two temperament lines were generally small and their possible influence on the display of maternal behaviour in the two temperament lines would have to be demonstrated.

Afferent and efferent connections of the cortical and medial nuclei of the amygdala in sheep

The cortical (CoA) and the medial (MeA) nuclei of the amygdala are involved in the processing of olfactory information relevant to social recognition in the ewe. To better understand the neural pathways responsible for these effects, the connections of both CoA and MeA with the telencephalic and diencephalic regions were studied by injecting an anterograde (Biotin-Dextran-Amine, BDA) or a retrograde (Fluorogold, FG) neuronal tracer into either the CoA or the MeA. Concerning the primary olfactory structures, the CoA receives inputs from both the main olfactory bulb and the accessory olfactory bulb (AOB), while the MeA is innervated by cells only from the AOB. Among the other olfactory structures, only the entorhinal cortex and the tenia tecta are connected with both the CoA and the MeA. With respect to the other secondary olfactory structures, the connections with the CoA and the MeA show segregating neuronal routes. The CoA is connected with the accessory olfactory nucleus, the piriform, the endopiriform and the orbitofrontal cortices while the MeA exhibited connections with the nucleus of the lateral olfactory tract, the perirhinal and the insular cortices. Concerning the diencephalic structures, only the MeA receives projections from the PVN and the MBH. On the other hand, we showed that the BNST is the major site of connection with both the CoA and the MeA. Reciprocal projections were observed between the CoA and the MeA and between both nuclei and the basal or the lateral nuclei of the amygdala with the exception of the CoA which does not send inputs to the lateral nucleus. These data are discussed in relation with olfactory learning in the context of sexual and maternal behavior in sheep.

Inactivation of the medial preoptic area or the bed nucleus of the stria terminalis differentially disrupts maternal behavior in sheep

The present study was designed to investigate the role of the medial preoptic area (MPOA) and the bed nucleus of the stria terminalis (BNST) in the onset and maintenance of maternal behavior in sheep. In a first experiment, the MPOA or BNST were transiently inactivated during the first 2 h postpartum in primiparous ewes with the use of the anaesthetic lidocaine. MPOA inactivation greatly impaired the display of maternal behavior whereas inactivation of BNST or of adjacent sites (septum or diagonal band of Broca) or infusion of cerebrospinal fluid did not. In a separation/reunion lamb test (S/R) performed at 2 h postpartum, ewes with MPOA inactivation exhibited little reaction after separation of their lambs and did not show any motivation to reunite with them. Ewes with BNST inactivation showed intermediate performances in the S/R test. Moreover, in control ewes that were maternal for the first 2 h postpartum, MPOA or BNST inactivation performed in the following 12 h induced deficits in the S/R test, indicating that the MPOA and to a lesser extent BNST are also involved in the maintenance of maternal behavior. A second experiment showed that, in multiparous ewes, MPOA inactivation at parturition induced less deficit in the display of maternal behavior and in the S/R test than in primiparous mothers. These findings indicate that the MPOA and, to some extent, the BNST are functionally involved in the initiation and in the maintenance of maternal behavior in sheep, but this involvement is influenced by maternal experience.

Prepartum plasma estradiol and postpartum cortisol, but not oxytocin, are associated with interindividual and breed differences in the expression of maternal behaviour in sheep

Consistent, individual differences in the expression of maternal behaviour have been described in several species including the sheep. The neuroendocrine mechanisms underlying the onset of maternal behaviour in the sheep have been described, although the relationship between hormonal events and individual differences in behaviour has yet to be determined. In this study, we examined whether the individual differences in plasma estradiol, progesterone, oxytocin and cortisol concentrations were related to observed individual and breed differences in maternal behaviours in two breeds of sheep (Scottish Blackface and Suffolk) known to differ in maternal behavioural expression. Maternal estradiol concentration increased rapidly before parturition and was higher in Blackface ewes than Suffolk ewes. Plasma progesterone declined before parturition and was higher in Suffolk than Blackface ewes. Prepartum estradiol, but not progesterone, was related to individual differences in maternal grooming of the lamb. Plasma oxytocin did not differ between breeds in late gestation. There was a tendency for oxytocin to be higher in Blackface than Suffolk ewes immediately after birth. However, there were no significant relationships between prepartum or postpartum oxytocin and any maternal behaviours. Plasma cortisol was higher in Blackface than Suffolk ewes in the last days of pregnancy but rose in both breeds over the last 24 h before parturition and did not differ at delivery. Cortisol peripartum was negatively related to individual differences in maternal affiliative behaviours. These data suggest that estradiol, and potentially cortisol, may mediate individual differences in maternal behaviour in sheep.

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

Maternal behavior in sheep is characterized by the rapid establishment of individual recognition of the lamb through the use of different sensory modalities. Olfactory recognition mediates acceptance at suckling whereas visual/auditory cues are involved in recognition from a distance. This study investigates (a) the timing of both types of recognition and (b) whether they can be influenced by maternal experience. Olfactory recognition was assessed at lambing, 30 min, 1, 2, or 4 hr postpartum by presenting successively an alien and the familiar lamb. Recognition at a distance was assessed at 6, 8, and 12 hr postpartum by using a two-choice test between the familiar and an alien lamb. A majority (33/51) of ewes showed selectivity at suckling as early as 30 min after parturition, and no differences due to maternal experience were observed. By contrast, in the two-choice recognition test, multiparous ewes showed a preference for their familiar lamb at 6 hr whereas primiparous mothers did so only after 24 hr of mother-young contact: The performance of biparous mothers was intermediate. Thus, both types of recognition can be rapidly established after parturition, and maternal experience has a differential effect on the dynamics of these learning processes.

Physiological Correlates of Maternal–Offspring Behaviour in Sheep: A Factor Analysis

The onset of maternal behaviour in sheep is controlled by levels of oestrogen and progesterone in gestation and the release of oxytocin during delivery. Factor analysis was used to investigate the relationships between maternal behaviour, offspring behaviour, and maternal ovarian hormone levels during gestation in sheep. Ewes gave birth to lambs following embryo transfer between two breeds (Suffolk and Scottish Blackface), which differ in their expression of maternal behaviour. Plasma oestradiol-17β concentration was significantly higher in Blackface ewes in the last 6 weeks of pregnancy, whereas plasma progesterone was higher in Suffolk ewes in early and mid gestation. Factor analysis revealed three factors that accounted for 50% of the total variation between variables. Factor 1 described lamb activity and had positive loadings for lamb behavioural latencies immediately postpartum, and negative loadings for sucking frequency. Factor 2 described some aspects of ewe maternal behaviour, and had positive loadings for ewe–lamb separation and lamb vocalisation, and negative loadings for ewe grooming behaviour and plasma oestradiol concentration. Factor 3 described ewe and lamb-sucking interactions, and had positive loadings for ewe moving as the lamb made sucking attempts, and negative loadings for ewe and lamb vocalisation. Factor 1 scores were significantly affected by lamb breed: Suffolk lambs received positive scores, indicating a longer latency to right and stand, whereas Blackface lambs had negative scores. Maternal progesterone concentration was significantly correlated with Factor 1 scores. Factor 2 and 3 scores were significantly affected by ewe breed. This study has shown that there are two behavioural axes to maternal behaviour in sheep, and that maternal oestradiol concentration is related to affiliative behaviours (e.g., grooming) but only weakly to ewe responsiveness to lamb-sucking attempts.

Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections

The olfactory bulb (OB) is involved in the processing of olfactory information particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gold, was injected into the olfactory bulb of seven ewes. By using immunocytochemical techniques, retrogradely labeled neurons were colocalized with choline acetyltransferase, tyrosine hydroxylase, dopamine-β-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluoro-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfactory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled neurons were observed in the taenia tecta, the septum, the nucleus of the lateral olfactory tract, the preoptic area, the lateral hypothalamic area, the mediobasal hypothalamus, the lateral part of the premammillary nucleus, the paraventricular nucleus of the hypothalamus, the paraventricular thalamic nucleus, the central grey, the substantia nigra (SN), the ventral tegmental area (VTA), the lateral nucleus to the interpeduncular nucleus (lIP), the raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the lIP and the LC. Cholinergic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical branch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the lIP. These data are discussed in relation with olfactory learning in the context of maternal behavior in sheep.

Maternal behaviour in sheep (Ovis aries) following administration of opioid agonists

Aims. As kappa(κ)-opioids have marked effects on pain threshold in sheep during oestrus, late pregnancy and after birth, a study was undertaken to determine if к-opioids also had other roles during these states. Methods. Opioid agonists (GR89696, DAMAGO) were administered into either the lateral hypothalamus (LH) or amygdala of non-pregnant sheep (n = 5) or pregnant sheep (n = 15) in late pregnancy (n = 5) within 12 h of birth (n = 5) or in the third week after birth (n = 5). Cortisol, behavioural and electrocardiographic responses to an auditory stimulus were assessed with and without drug administration, as was feed consumption and suckling events. Results. In non-pregnant sheep, DAMAGO injected into either the LH or amygdala had little effect on the response to the auditory stimulus but when injected into the LH did decrease food consumption. GR 89696 had no obvious effects. In late pregnancy, cortisol and heart rate responses to the auditory stimulus were significantly reduced compared to the non-pregnant animals irrespective of treatment. This was also the case in the third week after birth. Immediately post-partum cortisol responses were closer to that seen in the non-pregnant animal. In late pregnancy and both post-partum periods, GR 89696 in the LH significantly increased feed consumption while DAMAGO had no significant effects. GR 89696 injected into the amygdala reduced the behavioural response to the auditory stimulus in late pregnancy and both post-partum periods. Conclusion. Changes in sensitivity to opioids occur in both the amygdala and LH with pregnancy and after birth. These may influence maternal behaviours and feed intake.

Corticotrophin releasing factor mRNA expression in the sheep brain during pregnancy, parturition and lactation and following exogenous progesterone and oestrogen treatment

In the multiparous ewe, intracerebroventricular (i.c.v.) infusions of corticotrophin releasing factor (CRF) act centrally to facilitate the induction of maternal behaviour if administered with vaginocervical stimulation. Changes in CRF mRNA expression in the brains of multiparous ewes were therefore examined as a function of late pregnancy, parturition and lactation using in situ hybridisation histochemistry. As the induction of maternal behaviour in sheep is steroid dependent, a comparable analysis was undertaken in ovariectomised ewes treated with the sex steroids oestrogen and progesterone. Changes in CRF mRNA were quantified in the paraventricular nucleus (PVN) and in the bed nucleus of the stria terminalis (BNST). Expression levels in both the PVN and BNST were unaltered during pregnancy and lactation, but were significantly increased immediately post partum. CRF expression in the BNST, but not in the PVN, was significantly increased in response to treatments with progesterone and oestrogen alone or in combination, although there were no significant differences between treatments. These results indicate that CRF mRNA expression is increased in neuroanatomical locations relevant to the control of maternal behaviour when this behaviour is induced or, in the case of steroid influences on the BNST, is inducible by vaginocervical stimulation. They also indicate, that CRF mRNA expression in the BNST and PVN is differentially influenced by sex steroids.

Involvement of the main but not the accessory olfactory system in maternal behavior of primiparous and multiparous ewes

The respective roles of the main and accessory olfactory systems in the development of maternal behavior and selective suckling were investigated in parturient primiparous and multiparous ewes. Vomeronasal nerve section before parturition did not disturb either maternal behavior or maternal selectivity at suckling. By contrast, anosmia induced by zinc sulphate infusion had significant effects on the onset of maternal behavior in primiparous ewes. The onset of licking and of suckling were delayed and licking times and maternal bleats were reduced. Such disturbances were not observed in multiparous anosmic ewes, indicating that experience can compensate for the loss of olfactory information. On the other hand, anosmia prevented selective care regardless of maternal experience. Our results underline the importance of the main olfactory system for the development of adequate maternal behavior in sheep.

Maternal behaviour in sheep and its neuroendocrine regulation.

Non-parturient sheep, hormonally primed and presented with newborn lambs are, at best, indifferent to them and if approached by the lamb may show violent rejection. However, non-gestant ewes primed with oestrogen and progesterone, but given vaginocervical stimulation, do show a rapid onset in maternal behaviour. This stimulation is ineffective in promoting maternal behaviour with epidural anaesthesia. Vaginocervical stimulation increases the release of oxytocin into cerebrospinal fluid and in-vivo microdialysis has revealed high levels of oxytocin release in limbic brain areas known to be important for maternal behaviour. Oxytocin, when given intraventricularly, produces the full complement of acceptance and suckling behaviour in non-gestant ewes. Although ineffective when given alone, opioids potentiate the release of oxytocin in the limbic brain and increase the intensity of maternal responding, while the opioid receptor blocker, naltrexone, prevents both maternal induction and oxytocin release. This neural basis for maternally motivated behaviour may be equally relevant to human behaviour, although the mechanisms available for addressing these peptidergic systems have clear differences.

Autoradiographic detection of vasopressin binding sites, but not of oxytocin binding sites, in the sheep olfactory bulb

Oxytocin facilitates maternal behaviour in sheep. In the present study, we searched for the presence of oxytocin and vasopressin binding sites in the sheep olfactory bulb, a brain area which is thought to be involved in specific bond formation between the ewe and its lamb. Using in vitro autoradiography, we observed binding of triated vasopressin to the glomerular layer of the olfactory bulb. Competition studies performed with structural analogues and the use of a 125I-labelled linear vasopressin antagonist suggested that sites which bind vasopressin are V 1 type receptors. In contrast, specific binding sites for oxytocin in the olfactory bulb could be detected neither in control females, nor in ovariectomized females treated with estradiol nor in postparturient ewes, although such sites were present in the uterus.

Mammalian parenting: biochemical, neurobiological, and behavioral determinants

Norman A. Krasnegor: Biological and behavioral determinants of parenting in mammals: An introduction Part I. Four perspectives on parental behavior: Leon Eisenberg: The biosocial context of parenting in human families Martin Daly: Evolutionary theory and parental motives Jay S. Rosenblatt: Landmarks in the physiological study of maternal behavior with special reference to the rat Roger A. Gorski: Structural sexual dimorphisms in the brain: implications for parental behavior Part II. Biochemical correlates of parenting: Robert S. Bridges: Endocrine regulation of parenting behavior in rats Bruce B. Svare: Maternal aggression: hormonal, genetic, and developmental determinants Pascal Poindron, & Frederic Levy: Physiological, sensory, and experimental determinants of maternal behavior in sheep and goats C.L. Coe: Psychobiology of parental behavior in nonhuman primates Alison S. Fleming: Hormonal and experiential correlates of maternal responsiveness in human mothers Michelle P. Warren, & Barbara Shortle: Endocrine correlates of human parenting: a clinical perspective Part III. Neurobiological correlates of parenting: Michael Numan: Neural control of maternal behavior Thomas R. Insel: Oxytocin and maternal behavior E. Barry Keverne, & K.M. Kendrick: Neurochemical changes accompanying parturition and their significance for maternal behavior Barbara K. Modney, & Glenn I. Hatton: Motherhood modifies magnocellular neuronal interrelationships in functionally meaningful ways C.E. Grosvenor, G.V. Shah, & W.R. Crowley: Role of neurogenic stimuli and milk production in the regulation of prolactin secretion during lactation Part IV. Biobehavioral correlatesof parenting: Craig H. Kinsley: Prenatal and postnatal influences upon parental behavior in rodents Susan A. Brunelli, & Myron A. Hofer: Parental behavior in juvenile rats: environmental and biological determinants M. Leon, R. Coopersmith, L.J. Beasley, & R.*M. Sullivan: The role of mother-young contact in maternal care Jeffrey R. Alberts, & David J. Gubernick: Functional organization of dyadic and triadic parent-offspring systems Warren G. Holmes: Parent-offspring recognition in mammals: a proximate and ultimate perspective M.W. Yogman: Male parental behavior in humans and nonhuman primates Part V. Future directions in research research on mammalian parenting

Influence of the blood concentration of prolactin on the length of the sensitive period for establishing maternal behavior in sheep at parturition

The fading of postpartum maternal interest for the neonate (sensitive period) in ewes separated from their young at lambing is delayed when parturition is induced with 20 mg of estradiol benzoate (EB). An experiment was carried out to investigate the role of prolactin in this phenomenon. The sensitive period was studied in three groups of parturient ewes. In all groups lambs were removed at birth and reintroduced to their mothers 24 hr later. Maternal acceptance was tested at this time. In group 1 (dexamethasone D), ewes were induced to lamb with dexamethasone (15 mg im). In group 2 (EB), ewes were treated with 20 mg of estradiol benzoate (im). In group 3 (EB + CB 154) ewes received 20 mg of EB as in group 2 and 1 mg of CB 154 (sc) every 12 hr to prevent the enhanced secretion of prolactin which normally occurs after EB injection. The concentration of prolactin was highest in group 2 (EB), lowest in group 3 (EB + CB), and intermediate in group 1 (D) ( p ⩽ 0.001 between groups). By contrast, the proportion of ewes showing maternal behavior was similar in groups 2 and 3 ( 15 23 and 17 22 ), both of which differed from group 1 ( 3 22 ; p ⩽ 0.005 ). It is concluded that the lengthening of the sensitive period for establishing maternal behavior in sheep following EB induced parturition is not related with high levels of prolactin in the peripheral circulation.

Importance of the characteristics of the young in the manifestation and establishment of maternal behaviour in sheep.

The role played by the lamb in the regulation of maternal behaviour of the ewe around parturition was investigated in three experiments. In the first, the spontaneous manifestation of that behaviour was observed in parturient ewes when their lambs were swapped with either newborn or 12 to 24-hr old alien lambs. The ewes were undisturbed, or only slightly so, when their lambs were exchanged for alien newborn. In contrast, very obvious and significant differences were observed when swapping involved 12 to 24-hr old lambs. In the second experiment, ewes totally separated from their lambs at birth and for 12 hrs accepted a newborn alien lamb more readily than their own 12-hr old lamb at the time of reunion. In the third experiment, ewes were maintained in partial contact with their lambs for 12 hrs and maternal behaviour was tested at that time. The ewes remained maternal up to the time of testing only if they could smell their lambs. It was concluded that some characteristics of the newborn lamb are necessary for the development of adequate maternal behaviour.