Intervenciones nutricionales en edades tempranas para optimizar la función de la microbiota ruminal, la salud digestiva y la productividad animal

Abstract

The rumen is a fermentation chamber that enables ruminants to efficiently digest fibrous diets. This organ harbours a complex and diverse microbial community which makes it difficult to achieve a successful modulation of its activity. The first weeks of life of the animal when the ecosystem is being developed and therefore have high plasticity represent an interesting opportunity of modulation. Different interventions applied during the first weeks of life can allow the modulation and promotion of the rumen microbial colonization and rumen development, which is of great importance specially in artificial milking systems, where kids are quickly separated from their dams and therefore lack a natural source of colonization. This thesis aimed to evaluate several strategies to accelerate the rumen microbial development and to delve into the knowledge of the different factors that modulate the rumen microbiota. The first experiment of the thesis attempted to identify, under in vitro conditions, the mature rumen microbiota with a greater potential to be used as inoculum in newborn goats (Publication 1). Fresh rumen fluid sampled after feeding was found to be the inoculum that promoted a higher fermentative activity and therefore it was chosen for the following in vivo study. In this second experiment (Publications 2 and 3) newborn goat kids were daily inoculated until weaning under artificial-rearing conditions to assess the effects of this intervention on rumen development. This study showed that the inoculation with fresh rumen fluid in goat kids improved rumen fermentative activity and accelerated the rumen microbial colonization before weaning, as shown by the greater concentration and absorption of fermentation products such as butyrate (+50 %) and the more abundant and diverse microbial community (P < 0.05). Furthermore, Inoculated kids had a greater weight gain immediately after weaning, possibly because of their higher forage intake (+44 %) and complex rumen protozoal community. While animal growth was unaffected by inoculation, some of its positive effects also persisted after weaning. A subsequent study (Publication 4) aimed to evaluate the effects of mimicking the former microbial transmission to newborn goat kids until weaning by the presence of non-lactating adult companions in the same pen. This management strategy also resulted in an earlier rumen microbial development in goat kids, as shown by the presence of a diverse bacterial (+132 phylotipes), protozoal and methanogens communities at weaning, which better resembled those of the adults. Effects on rumen activity and animal performance were not as clear as with the direct inoculation but higher butyrate (+ 45 %) and ammonia concentrations suggest improved fibrolytic and proteolytic activities. These findings suggest that under artificial-rearing conditions, the direct inoculation of young ruminants with rumen fluid from adult animals, or indirectly by the mere presence of adult companions, allows an acceleration of the microbial and functional rumen development with positive effects during the weaning period. Concurrently, this thesis evaluated the role of the salivary bioactive components in the regulation of the rumen microbial populations and their fermentative activity by incubating with different saliva fractions and from different donors. Incubating with a high proportion of filtrated saliva (without microbiota but with salivary proteins) boosted the levels of rumen fermentative activity (Publication 5). The use of autoclaved saliva led to a very divergent microbial community composition, with greater abundance of Proteobacteria and lower of Prevotellaceae, compared to the communities resulting from incubation with non-autoclaved goat’s or sheep’s saliva (Publication 6). These findings suggest that direct and, to a lesser extent, indirect inoculation of rumen microbiota improved the rumen development in goat kids at weaning and that the bioactive components of saliva selectively modulate the rumen microbial populations and their activity for a suitable host-microbiota association.