The colonization of the digestive tract in animals begins soon after birth or hatching and the normal microbiota changes dramatically during the life of the host. The composition of gastrointestinal microbiota differs between animal species, between individuals within the same species and between the body sites of the host. The gut microbiota is a complex interactive community of organisms and its functions are the result of activities of all microbial components. Together with the host, the microorganisms constitute an ecological system, beneficial for the host, as well as for the microbial species. In principle, the role of gut microbiota in animals is the same as in humans—salvaging energy from the undigested feed components through fermentation, providing the basis for a barrier that prevents pathogenic bacteria from invading the gastrointestinal tract, protective functions together with the gut immune system, a role in metabolism of xenobiotics and contribution to the vitamin and amino acids requirements of the animals (1). Some of these functions are emphasized in farm animals with regard to their environment, character of their feed and the economy of farm animals' rearing. The composition and metabolism of the gastrointestinal microbiota affects the performance of farm animals in many ways, especially in the young, which are subjected to many stressful conditions.

Farm animals can be divided into three main groups according to the degree of development of their gastrointestinal tract and efficacy of feed digestion: (1) omnivorous animals—the feed of plant origin with small content of cellulose and lignin, as well as the feed of animal origin is easily and quickly digested with a help of enzymes produced in the gastrointestinal tract of the animal (pigs), (2) carnivorous animals—under natural conditions they consume mostly feed of animal origin, (3) herbivorous animals—consume feed of plant origin with high content of cellulose and lignin, which the animal is able to digest exclusively through microbial fermentation by its gastrointestinal microbiota (ruminants, horses). Herbivorous animals have some part of their gastrointestinal tract adapted to microbial fermentation. The ruminants are polygastric animals with foregut capacity 150-180L in adult cows. In horses, which are monogastric, the caecum with capacity 100-140L is developed for microbial fermentation of lignin and cellulose.

The greatest differences in the composition of the microbiota of the gastrointestinal ecosystem have been shown to occur between ruminants and monogastric animals. Gradual changes in the composition of the gastrointestinal microbiota that take place within an animal species are related to age (2). At an early age the microbiota of the digestive tract of young animals is very similar. With the exception of poultry, this similarity is related to the intake of maternal milk. During the suckling period, bacteria, which can utilize the components of milk, predominate in the upper tract, and the milk constituents evidently largely determine which microbe can be implanted in the intestines. The forestomachs of ruminants have not yet started functioning and the physiology of the digestive tract compares to that of monogastric animals. After the animals start to consume creep feed and they are finally weaned, an adult type of microbiota begins to develop in the upper and lower intestinal tract. At the same time the main site of bacterial fermentation changes from the stomach to the large intestine or, in ruminants, to the rumen.

Due to progressing of age, changes in the composition of the ingested feed and a different morphological and functional development of the gastrointestinal tract, certain differences gradually occur in the composition of the microbiota in calves, lambs, suckling piglets and chicks that are typical for the given farm animal species. The gut ecosystem of adult animals is stable and changes only due to the effects of external factors of an adequate intensity (long-lasting change of feeds, stress, administration of antibiotics).

Pregnancy And Childbirth

Pregnancy And Childbirth

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