Do newborn puppies have their own microbiota at birth? Influence of type of birth on newborn puppy microbiota

Highlights

• Better understanding of the canine meconium and placenta microbiota is provided.

• Colonization of the newborn microbiome likely begins prior to birth, as microbes have been isolated from the placenta.

• The puppies’ meconium and placenta at birth harbor a variety of microbes.

• Type of delivery has an impact on puppies’ weight gain.

• Bacterial colonization is important considerations for puppies’ weight gain in the first few days of life.

Abstract

With recent research in humans, a hypothesis known as the sterile womb paradigm has been challenged. The objectives of this study were to determine the presence of placental and fetal microbiomes in dogs, the effect of different types of parturition on the fetal microbiome, and the effect that the fetal microbiome has on early puppy development.

A total of 96 newborn puppies from 17 dams were included in the study. Puppies were divided into two groups depending on the type of parturition (vaginal birth (VB) or cesarean section (CS)). Immediately after birth, swabs of the placenta and meconium were taken. Swabs of the oral and vaginal mucosa of the dam were taken in the second half of the pregnancy and just before parturition. All samples were analyzed with a classical bacteriological examination, and bacterial colonies were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The weight gain of each puppy was tracked daily in the first 7 days postpartum.

Bacteria from several different genera were isolated from 86.5% of meconium samples and 57% of placenta samples. While the meconium microbiota resembled bacteria from the maternal vagina in VB puppies, the meconium microbiota of puppies born by CS indicated a relative resemblance to maternal oral and vaginal microbiota. A statistically significant difference in the relative growth rate between puppies born by VB and CS was found (p < 0.05), with puppies born by VB gaining weight faster compared to the CS group. This difference was even more noticeable when VB puppies were compared to puppies born by elective CS. Puppies born without a detectable meconium or placental microbiota showed a slower growth rate than those with a meconium microbiota, regardless of the type of parturition (p < 0.05).

The findings of this study provide new information about the placental microbiome in healthy pregnant dams and suggest intrauterine colonization of the fetus in dogs. It seems that the type of delivery and bacterial colonization might be an important consideration for the weight gain in puppies in the first few days of life.

Introduction

Until the second half of the 19th century, it was believed that a fetus develops in a sterile environment and that the initial bacterial colonization of the newborn occurs while traveling through the maternal birth canal. This hypothesis is also known as the sterile womb paradigm and has remained dogma for more than a century [1]. However, many recent studies employing modern sequencing technologies in humans suggest that the uterus, placenta, amniotic fluid, meconium and umbilical blood from healthy pregnancies contain bacterial communities [[2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]]. These studies suggest that the placental microbiome may initiate colonization within the fetus [[2], [3], [4]] and that bacterial transmission through the placental barrier is a part of the normal developmental process of the fetus [1].

Several studies have shown the influence of delivery type on the composition of the gut microbiota of newborn babies. The gut microbiota of vaginally born (VB) infants is composed of bacteria present in the vagina of the mother but also includes bacteria present in the mother’s gut [14,15]. In contrast, the gut microbiota of infants born by cesarean section (CS) resembles maternal skin and oral microbiota [16,17]. However, it needs to be mentioned that in these studies, the samples of the infants’ gut microbiota were obtained a few days after birth and not immediately after parturition.

The presence of an endometrial microbiome has been reported in healthy cows [[18], [19], [20], [21]], giant pandas [22] and dogs [23]. Microbes have also been found in foal amniotic fluid [24], newborn calf meconium [25] and pregnant bovine uterus [26]. Recently, a transplacental translocation of Staphylococcus aureus through the maternal/fetal barrier to the fetus was reported in a pregnant ewe [27].

While a layer of maternal endothelium separates canine fetal chorion from maternal blood (endotheliochorial placenta), in humans, maternal blood comes into direct contact with the fetal chorion (hemochorial placenta). This direct connection in humans allows for a much better exchange of substances, including immunoglobulins, between the mother and the offspring. While human babies are born with high levels of immunoglobulins, in dogs, only 5%–10% of immunoglobulins are transferred through the endotheliochorial placenta from the mother to her offspring [28]. In dogs, the transplacental exchange of antibodies is very limited and mainly occurs during the last third of gestation in a specific placental region with a hemochorial organization [29]. This different structure of the canine placenta could minimize the transmission of bacteria from the endometrium and blood to the placenta and fetus and thereby prevent the formation of the placental microbiome and early intrauterine microbial colonization of the puppy.

There is a paucity of knowledge about the placental and fetal microbiomes in dogs. The objectives of this study were to determine the presence of placental and fetal microbiomes in dogs and evaluate the effect of different types of parturition (VB vs. CS) on the fetal microbiome and early puppy development.