ALL CHICKENS ARE NOT EQUAL
I read recently a very interesting study that I would like to share with you today. This work has been published in 2021 by the Danish company Christian Hansen, specialist in bacterial probiotics. This experiment has been looking at the correlation between the growth on broilers and the composition of their intestinal microbiome.
Broiler production is based upon a multiple-generation procedure of purebred genetic lines and their crosses. Broiler purebred lines have low heterozygosity and are very closely related to each other. Intensive selection processes over the past five decades have decreased genetic variation within purebred lines resulting in a distinctly low genetic variation of the broiler. When housed under the same conditions and fed the same feed, one should think that broilers would have a relatively comparable growth and that a certain uniformity in final body weight (BW) could be achieved. Nevertheless, at slaughter, variations in BW of 11–18% in mixed sex flocks are regularly observed, and 8–10% have been reported even for male-only flocks. Poor uniformity translates to decreased profitability due to devaluation of carcasses not complying with the processing plant and market specifications. At the same time, it is desirable to achieve healthy, productive birds reaching a high final bodyweight. The low genetic variation is not expected to solely drive this variation in final BW, hence other factors must also play a role. Poor management practices or health problems can cause some birds to have reduced access to feed and water. The gut microbiome is a player to also consider with regards to carcass uniformity. The composition and activity of the gut microbiome is predominantly shaped by dietary and environmental factors and to a smaller extent by host genetics and is known to impact animal health and productivity.
The Lachnospiraceae has for instance, consistently been associated with high chicken productivity, possibly due to the anti-inflammatory potential of this short chain fatty acid (SCFA) producing family. Lactic acid bacteria are also associated with chicken performance. On the other hand, the genus Escherichia and the family Enterobacteriaceae correlate frequently with low productivity due to a high pathogenic potential within these taxa. Enterobacteriaceae is recognized as a pro-inflammatory marker of imbalance of the gut microbiota (dysbiosis) in poultry.
In this new study, 218 male newly hatched Ross 308 broilers chickens were placed in one pen and reared for 37 days. Animals housed together share microbiomes to a large extent due to the shared local environment and behaviors such as coprophagy and pecking/preening activities. We can therefore expect that homogeneously reared group would present similar caecum microbiome profiles.
At the end of the study, the 25 heaviest (the Big) and 25 lightest (the Small) birds were selected, sacrificed and contents from the cecal sacs were sampled.
After 37 days, birds averaged 2379 g. The 25 heaviest birds (Big) averaged 2887g with the biggest bird achieving 3134 g. The 25 lightest birds (Small) had a mean BW of only 1836 g and the smallest one weighing 1514 g.
When we compared the caeca content composition of these groups, differences between the Big and Small chickens were investigated using a descending taxonomic rank approach, starting from phylum rank for a high level overview, then family, genus and ultimately the MAG level, which is comparable to species level or in some cases even strain level.
Six phyla were represented across all samples: Firmicutes, Actinobacteriota, Bacteroidetes, Verrucomicrobiota, Proteobacteria and Cyanobacteria. Firmicutes was the dominating phylum both in Big birds (66%) and Small birds (58%).
We noted that the Big group had 31 bacteria species more abundant than the Small group and only 5 species that were less abundant. Among the most abundant one, we can list Lachnospiraceae, Eisenbergiella, Christensenellales, Faecalibacterium, Flavonifractor, Butyricicoccus, Bifidobacterium.
At the opposite among the species more abundant in the Small group we identified Akkermansia associated to leanness and Escherichia acting as proinflammatory.
The Big birds had a higher diversity compared to the Small birds from the same pen. Microbial diversity of the gastrointestinal tract is a solid marker of gut health, as mostly demonstrated in humans. In poultry, high diversity has also been linked to high productivity and gut health. The higher diversity and thus improved microbiome functionality could therefore have contributed to the improved growth of the Big chickens in that study.
All the species that were more abundant in the Big group are recognized are major producer of Short Chain Fatty acids, especially butyrate. The SCFA butyrate is specifically a critical energy-source for the colonocytes and exerts numerous beneficial effects, including growth promotion, antimicrobial activity, immunomodulation, and anti-inflammatory activity; inclusively these attributes can lead to a reduction in pathogens. Of butyrate- producing taxa with higher levels in the Big birds were Eisenbergiella, Eubacterium, Faecalicatena and Flavonifractor.
Among other SCFA-producing taxa enriched in the Big chickens were Fusicatenibacter which produce formate and acetate.
The interesting question behind this study is to understand why some chicken gets a more diverse and development microbiome although all chickens were raised in the same environment, eating the same feed from the same feeder in the same barn. It may come from unnoticeable micro-events at the early life of the birds. A self-enforcing cascade of events might happen: some birds have by chance poorer microbiome, leading to reduced nutrient absorption and the birds not feeling as fit as the others. This can lead to social stress by lower ranking and a viscous circle of reduced feed intake and picking in the litter with increased ingestion of pathogenic and dysbiosis-related bacteria starts. Ultimately, this leads to an even more suboptimal microbiome. At some point, the difference in bodyweight itself will force further differentiation, as larger birds are requiring more feeder space for a longer duration of time. These heavy broilers will be harder to push aside when lighter birds want to make their way to the feeder and drinker.
Beneficial early life programming of the gut microbiome is crucial for the development of the immune system, establishment of gut health and even behavior. Such programming may be achieved through early probiotics distribution, additives promoting early microbiome development and/or seeding environment with beneficial bacteria. These intervention examples might also be helpful in overcoming microbiome heterogeneity and thus bodyweight heterogeneity.
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