The influence of the conventional microflora on the body temperature of the chick

Maternal antibiotics disrupt microbiome, behavior, and temperature regulation in unexposed infant mice

Maternal antibiotic (ABx) exposure can significantly perturb the transfer of microbiota from mother to offspring, resulting in dysbiosis of potential relevance to neurodevelopmental disorders such as autism spectrum disorder (ASD). Studies in rodent models have found long-term neurobehavioral effects in offspring of ABx-treated dams, but ASD-relevant behavior during the early preweaning period has thus far been neglected. Here, we exposed C57BL/6J mouse dams to ABx (5 mg/ml neomycin, 1.25 μg/ml pimaricin, .075% v/v acetic acid) dissolved in drinking water from gestational day 12 through offspring postnatal day 14. A number of ASD-relevant behaviors were assayed in offspring, including ultrasonic vocalization (USV) production during maternal separation, group huddling in response to cold challenge, and olfactory-guided home orientation. In addition, we obtained measures of thermoregulatory competence in pups during and following behavioral testing. We found a number of behavioral differences in offspring of ABx-treated dams (e.g., modulation of USVs by pup weight, activity while huddling) and provide evidence that some of these behavioral effects can be related to thermoregulatory deficiencies, particularly at younger ages. Our results suggest not only that ABx can disrupt microbiomes, thermoregulation, and behavior, but that metabolic effects may confound the interpretation of behavioral differences observed after early-life ABx exposure.

Comparative biology of germ-free and conventional poultry

Interaction between the host and the enteric microbiome is highly complex. Microbial involvement in certain pathologies is moderately well established, but the contribution of the microbiome to animal welfare, behavior, sustainability, immune development, nutritional status, physiology, and maturation is less clear. A valuable experimental model to enable scientists to explore the role of the microbiome in various domains is to compare various phenotypes of a conventionally reared (CV) cohort with those in a germ-free (GF) state. A GF animal is one that is devoid of any detectable microbial life including bacteria, viruses, protozoa and parasites. The GF state is different from gnotobiotic animals where the microbiome is fully described, or ‘specific pathogen free’ (SPF) animals where a moderately normal microbiome is present but devoid of pathogenic microorganisms. Pioneering GF research in poultry in the late 1940s and 1950s has its origin in a need understand the mode of action of antibiotics. Early researchers quickly established that GF chicks responded differently to antibiotics than CV counterparts. The GF experimental model has since been exploited in many divergent fields including pathology, immunology, metabolism, anatomy, physiology, and others. The absence of a microbiome presents the host with a range of advantages and disadvantages. For example, GF chicks often grow more quickly and have lower feed conversion ratio (FCR) than their CV counterparts but may be less resilient to external stress and have a compromised immunological maturation rate. This review will summarize the literature on GF animal research with a special emphasis on poultry. The objective of the review is to establish a frame of reference to understand the extent of the role of the microbiome in animal health, welfare, nutrition, and growth, to provide opportunities for targeted modulation of the microbiome to achieve desired phenotypic responses whilst simultaneously minimizing unintended collateral effects.

The functionality of the gastrointestinal microbiome in non-human animals

Due to the significance of the microbiome on human health, much of the current data available regarding microbiome functionality is centered on human medicine. For agriculturally important taxa, the functionality of gastrointestinal bacteria has been studied with the primary goals of improving animal health and production performance. With respect to cattle, the digestive functions of bacteria in cattle are unarguably critical to digestion and positively impact production performance. Conversely, some research suggests that the gastrointestinal microbiome in chickens competes with the host for nutrients and produces toxins that can harm the host resulting in decreased growth efficiency. Concerning many other species including reptiles and cetaceans, some cataloging of fecal bacteria has been conducted, but the functionality within the host remains ambiguous. These taxa could provide interesting gastrointestinal insight into functionality and symbiosis considering the extreme feeding regimes (snakes), highly specialized diets (vampire bats), and living environments (polar bears), which warrants further exploration.

Modification of energy metabolism by the presence of the gut microflora in the chicken

Whether the association with gut microflora modifies the energy metabolism of chickens was investigated by varying the metabolizable energy consumption level from zero to above the maintenance requirement in the germ-free and conventional states. Single comb White Leghorn chicks were either fasted for 3 d (Expt 1), or fed for 6 d at a fixed daily meal intake of 2, 5 or 8 g/d (Expt 2), or 5, 10 or 15 g/d (Expt 3). Changes in carcass energy deposition and heat production indicated that when no dietary energy was available the presence of the gut microflora could benefit the birds by reducing energy losses, whereas when dietary energy was supplied the efficiency of energy utilization was reduced by the presence of the gut microflora. It was concluded, therefore, that the heavy burden of the gut microflora modifies energy metabolism by exerting a buffering or a counter-productive action on the energy utilization of the chicken.

Influence of the gut microflora on fasting heat production in chicks

1. The influence of the gut microflora on fasting heat production in chicks was investigated. 2. Single Comb White Leghorn chicks were fed on an adequate diet from 2 to 12 d of age and then fasted for 3 d. Fasting heat production was estimated from changes in body composition and energy content of droppings from days 1 to 3 of fasting. Measurements of body temperature and plasma thyroxine concentration were also made. 3. Body fat content was consistently higher in germ-free (GF) chicks than in conventional (CV) counterparts during the starvation period, whereas no difference was found in body protein content. The GF birds had a significantly higher body temperature than the CV controls with no change in plasma thyroxine concentration. 4. It was concluded that estimated fasting heat production of chicks was increased by the absence of the gut microflora.

Comparison of media for isolation of poultry intestinal bacteria

The effects of medium composition, incubation temperature, and length of incubation were determined for recovery of the predominant intestinal bacteria from turkey poults. Incubation of recovery media at 41 degrees C resulted in significantly higher counts than at 37 degrees C. In 2- and 3-week-old turkey poults. RGCAP-30, RGCAP-10, and RGCA-30 gave the highest recoveries of cecal bacteria. M98-5 was less effective and brain heart infusion agar was definitely inadequate. However, there was no significant difference between RGCAP-30 and brain heart infusion agar for recovery of duodenal bacteria. In older birds (6 weeks of age), M98-5 was equal or superior to the RGCA-based media. The choice of a primary isolation medium is thus dependent on the site to be sampled and the age of the bird.