A Common Marmoset Model of Mother-Infant Intervention for Breastfeeding Disorders in the Presence of Paternal Inhibition and Maternal Neglect

Summary

Here, we present a nonhuman primate model of mother-infant intervention for breastfeeding disorders in the presence of paternal inhibition and maternal neglect. The mate model video complements education to support primate and human caregivers with respect to infants with breastfeeding problems such as pain.

Abstract

Parents' psychological stress during the perinatal and neonatal periods continues to increase in an environment of declining birthrates, aging populations, and shrinking family sizes. The increase in child abuse and neglect cases, most likely by inexperienced and insufficiently knowledgeable parents, necessitates education on childcare and intervention techniques in nursing and midwifery training. In particular, attachment formation early in life between mother and infant is crucial. To accurately teach sensitive and comprehensive information on intervention techniques for mother-child attachment formation, realistic videos, and educational materials are necessary. Although pseudoeducational materials are available, they might be limited in explaining complex realism, particularly to support breastfeeding that involves both parents and child and that encourages interaction between the two.

In a previous study in a common marmoset (Callithrix jacchus) model, we experimentally controlled infant feeding and nurturing through 24 h of constant sensing and collected 1 month of quantitative data on psychological indices that possibly translated to psychological development. Age-dependent dynamic visualization of these data by multivariate analyses inferred causal relationships between early parental feeding and psychobiological rhythm formation. In the same primate model, we identified a spontaneous case of breastfeeding failure in which the father inhibited his neonatal infant's feeding and the mother appeared to abandon nurturing, leading to clinically significant weight loss in the infant.

Thus, we explored intervention techniques to promote mother-infant interaction. The mother was trained to allow the infant to spontaneously explore her breast. Initially, the mother refused to display the feeding pose potentially due to pain associated with breast engorgement. Massage was used to soften the breast and feeding was reintroduced. We hypothesize that activation of instinctive attachment formation mechanisms by encouraging spontaneity in each parent and child is the key to successful feeding intervention.

Introduction

The perinatal and neonatal periods are often stressful for parents. This is a particular problem in countries like Japan, where direct exposure to child rearing is limited given the countries' low birthrate, aging population, and tendency to live in nuclear families. This situation is exacerbated by a lack of institutionally supported education regarding child rearing¹. Against the background of this limited experience and the social problems associated with poverty, for instance, in younger couples, there is a high risk of postnatal growth failure related to breastfeeding issues in the presence of stress-related abuse and neglect by parents².

The establishment of breastfeeding by mothers separated from their infants after delivery is crucial for attachment formation and "the comparison between breastfeeding and formula feeding shows that the former has an effect on the development of rich emotions in newborns," suggesting a strong causal relationship between breastfeeding and attachment formation³. However, to improve early breastfeeding success and postnatal growth and development if there are medical problems in the infant or mother, it is often necessary to separate the infant from the mother to allow appropriate nutritional management of the newborn. Following the stabilization of the newborn, mothers must be provided guidance and support to successfully establish breastfeeding. Fathers, intimate partners, and other support individuals should be included in this instruction to learn how to nurture their child and provide appropriate support for breastfeeding⁴. Most of the available literature (e.g., "Environment and Nursing Intervention from Immediately After Delivery to Establishment of Breastfeeding") focuses mainly on interventions and support for mothers⁵. It is expected to be better taught to midwifery and nursing students' awareness and specific intervention skills to support breastfeeding that involves both the parents and child and that encourages interaction between the two.

Previously, we developed the common marmoset (Callithrix jacchus) as a small nonhuman primate model to explore the psychobiological basis of perinatal and neonatal interventions⁶. We designed a system that uses social scene-dependent changes^7,8,9 and biomolecular activities^10,11,12 to quantitatively identify developmental changes in the control of sensory (visual, auditory, tactile, olfactory) perception in different environments. Using principal component analysis (PCA), we were able to extract multiple explanatory behavioral factors, which allowed us to reproduce the complex neural network responsible for social psychological function in these animals. The results of this Behavior Output analysis for Quantitative Emotional state Translation (BOUQUET) method suggested that social interaction between adult males and females could be visualized quantitatively based on familiarity-dependent features in the same evaluation system¹¹. We hypothesized that differences in common marmoset behavior reflect each individual's psychocognitive learning in the past.

In this study, we compared animals in three conditions: siblings in a social environment where children interacted with each other, a single child that only experienced social interactions with their parent, and a situation similar to human foster care in which young were separated from any genetic family members. The BOUQUET analysis revealed quantitative differences in the time course of social response behavior development between groups, indicating that familial interactions (i.e., parents and siblings) during development influence the formation of social psychological functions¹³. In addition, we analyzed psychosocial development from postnatal day 15 to day 45 in marmosets using continuous infrared imaging in a situation replicating foster care in which formula was provided by the research staff. Data, including body surface temperatures, activity, and location preference, suggested the existence of unique age-dependent patterns. Further analysis indicated that experience during initial feeding periods may have significantly influenced behavioral rhythms after 1 month of development¹⁴. Circadian rhythms and their disruption are known to be closely related to mental functions that are required for human adaptability to an increasingly complex society, and their formation is influenced by early childhood experiences.

This report follows previous findings^11,13,14 to explore the feasibility of intervening in a case of breastfeeding failure in a common marmoset family displaying abuse-like behavior by the father and neglect-like behavior by the mother. While marmosets generally produce multizygotic multiples and are known for their communal raising of the offspring by not only the mother but also with the cooperation of the father and older siblings, this primate model involved a nuclear family, parents, and their only offspring, which aimed to mimic the current state of the human social condition. The first-time common marmoset parents exhibited disinhibited behavior followed by cessation of breastfeeding and infant abandonment, leading to the infant failing to thrive. The intervention and recovery process in this case of attachment dysfunction in a social feeding primate model was assessed through video records. The symptoms and treatment effects are indicated by an increase or decrease in body weight relative to the survival limit, referring to previously published criteria^15,16. The larger goal of this study is to determine the efficacy of human clinical interventions for the education of mothers and fathers who implement breastfeeding and the midwives who support them. Although the abandonment of vulnerable offspring with some problems by natural selection might be categorized as normal behavior for common marmosets, this clinical model aims to explore human evolutionary strategies of supporting health and well-being for the dignity of all life.

Protocol

This study protocol was approved by the Institutional Animal Care and Use Committee of Saitama Medical University (2476).

1. Animals

1. House a pair of parents with their first-time infants of common marmosets (Callithrix jacchus) who have no experience raising any infants in a light-sealed incubated cage, maintaining constant temperature (25-30 °C), and a 12 h light/dark cycle). Set light intensity per cage at 750-930 lx during the light period and 0 lx during the dark period. Ensure that the parents are healthy with respect to feeding and cleaning.
   NOTE: The cage was sized according to the Standards relating to the Care and Keeping and Reducing Pain of Laboratory Animals by the Japanese Ministry of the Environment.

2. The diagnosis of underweight and parental infant-rearing abnormality

1. Refer to the general diagnosis and intervention flows visualized in Figure 1 (A: Infant, B: Mother). When the infant is found to be underweight, choose intervention methods for the infant based on the presence or absence of five infant behaviors (crying, clinging to mother, head control, rooting reflex, sucking) and for the mother based on the presence or absence of five maternal behaviors (the will to feed, breast enlargement, infant's sucking acceptance, milk secretion, and pain expression).
   ​NOTE: Take care throughout to not cross-contaminate the animals' scent.

3. Animal characteristics

1. Gestational age at birth
   1. Make a note of the common marmoset's full-term gestation period of approximately 140-150 days. This compares to the human standard full term ¹⁷.
2. Birth and developmental weight
   1. Age and sex definition
      1. As a day-old notation, define birthdays as postnatal day 0 (PD 0). Define the sex of the infant by examination of external genitalia.
   2. Identification of congenital malformations or diseases
      1. Examine the infant to identify any congenital malformations or diseases, paying particular attention to those that might cause feeding difficulties (e.g., cleft palate).
   3. Body weight measurement
      1. Weigh the infant daily using a scale with 0.1 g increments to check their feeding volume. Prepare a clean plastic box or bowl lined with soft tissue paper to hold the infant and maintain its body temperature during weighing. Tare the prepared box or bowl on the scale, place the infant in the prepared container, and record the body weight. Weigh daily at approximately the same time to compare with the standard ^15,16.
         NOTE: Measure the weight with precautions to prevent the infant from escaping or being harmed while on the scale.
   4. Body weight gain graph
      1. Visualize a graph of body weight gain per day. The weight at birth and on the second day is expected to be more than 27 g and to then increase by approximately 1 g per day according to the colony records of neonatal infants' weight required for survival (Figure 2).
   5. Assessment of milk intake volume
      1. Assess milk intake volume by weighing the infant both before and after feeding. However, be aware that separating the infant from the parent for weighing may itself cause stress and interfere with nurturing behavior. If normal breastfeeding and growth are expected, reduce weight measurements to once daily for the first week.
   6. Crown, rump, and length measurement (CRL)
      1. Separate the infant from the parent gently and quickly measure CRL by laying the infant flat in the prone position against a ruler and determining the length from the top of the head to the base of the tail (Supplemental Figure S1). After measurement, immediately return the infant to the parent.
3. Breastfeeding behavior of the infant
   1. Confirm that the infant is performing four behavioral patterns (Figure 1A).
      1. Determine whether the infant is clinging to the mother's body sufficiently.
      2. Observe whether the infant's head is bent forward to the mother's body by its own whole body muscle tension.
      3. Note whether the infant explores and reaches the mother's nipple by itself as a human sucking "rooting" reflex with some parental help.
      4. Vocalizing a phee call^11,12 loudly when separated from its parents.
4. Mother's breastfeeding behavior and function
   1. Confirm these behavior patterns and functions in the mother (Figure 1B).
      1. Confirm the mother's cooperative acceptance of the newborn for breastfeeding.
      2. Confirm that when the mother's breast becomes taut, the mother encourages the infant to suckle, and then the breast becomes less taut and the teat protrudes.
      3. Support the mother's breastmilk secretion by pressing the breast side with the fingers (Figure 3A). Check that the breast tension is not too hard and is without engorgement.
         NOTE: Wear soft and thick cowhide gloves to prevent the mother from biting and hold the mother using the nondominant hand.
      4. Observe the mother's expression and look for signs of pain, such as tears in her eyes and her upper and lower teeth closed and exposed, which may be the cause of her refusal of the infant's suckling.
5. Father's parenting behavior
   1. Observe the father's parenting behavior. Observe whether the father is carrying the infant excessively, so much that it interferes with the mother's breastfeeding adequately and thus disrupts nursing. The father's assistance to carry the infants is usually limited.
6. Intervention targeting both the mother and infant to reestablish spontaneous breastfeeding
   1. When an underweight infant ( less than 27 g ) is found, observe the family relationship and search for any abnormal parental infant-rearing behavior. Potential parental abnormal behaviors pose a high risk of harming the infant or interfering with feeding (abuse) or abandonment of feeding (neglect).
   2. When the infant is too weak to explore or cling to the mother and initiate nursing by itself, separate it from the mother and give it a minimal amount of formula (e.g., 0.5 mL of Lebens Haihai, Wakodo at two-thirds concentration) by oral syringe, as needed based on body weight (Figure 1A,B).
   3. As the first intervention step aimed at the mother, soften the hardened nipple area by pressing and massaging in three steps from the areola base toward the nipple between fingers to open the milk duct (Figure 3B). Exude milk slightly from the teat for the odor to encourage the infant to explore.
   4. Next, hold the mother's body softly and lay the infant near the mother's breast to encourage it to search for the mother's nipple (Figure 1C). Guide the mother to raise her arms to improve nipple access for the infant. After the infant finds the nipple, continue the breast massage to assist with milk secretion. Confirm that the mother's breast is relieved of pressure, likely relieving the pain and the teat is protruding.
   5. During the intervention, provide occasional handling and build rapport with the family.
   6. Repeat this intervention one or more times per day until the mother voluntarily allows feeding and the infant learns to suck spontaneously. When the infant's feeding is inhibited by the father, remove the father from the family until the infant's development improves.

Results

Diagnosis of underweight and parental infant-rearing abnormality
A pair of five-year-old common marmosets (Callithrix jacchus) obtained from a colony at Saitama Medical University gave birth to their first set of offspring (twins) overnight in May 2019. This was a spontaneous vaginal birth. Only one of the offspring (a male) was found alive and embracing the mother's body. Another sibling was found dead, the birth weight (less than 25 g) and sex unclear, multiple hours after death. The prese...

Discussion

Parental care of infants in diverse species requires mutual physiological and psychological considerations^{7,9,10,12,13,14,18,19,20,21,22,}

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
			Specification
Common Marmoset			Self Breeding
			Mother 5 year-old Number: 1
			Father 5 year-old Number: 1
			infant 0-13 day-old Number: 1
Formula Milk			Lebens Haihai, Wakodo Number: 1
			distilled water
Plastic glove			powder-free
Syringe			1 mL Number: 1
Video Cemera			Sony Handycam Number: 1
			iPhone camera Number: 1
Weight Scale			0.1 g increment Number: 1