1 Poultry nutrition

Abstract

Nutrition is the most important environmental factor affecting development, health status, growth performance and profitability of poultry production. Feeds for poultry constitute up to 70-75% of total production costs. Poultry nutrition differs considerably from that of other livestock, which is determined by the specific anatomy of the gastrointestinal tract. Protein, energy, fat, fiber, minerals, vitamins, and water are of basic importance for poultry nutrition and their content in feeds must cover the requirement that differ depending on the bird's age and species. In general, feed protein must be of good value including the content of essential amino acids. Among them lysine, methionine, cysteine, threonine and tryptophan are the limiting ones. The main ingredient of poultry feeds are cereal grains, i.e. wheat and maize, which predominantly constitute an energy source because their protein content is insufficient for birds. Because of that cereals cannot be the only feed for poultry and must be combined with protein sources such as soybean or rapeseed meal, legume seeds or protein concentrates. Despite birds' requirement for nutrients and chemical composition of feeds are well known, nutrition must face many problems. One of the most important issues is to find alternatives to antibiotic growth promoters.

1.1 Introduction

Nutrition is the most important environmental factor affecting development, health status, growth performance and profitability of poultry production. Feeds for poultry constitute up to 70-75% of total production costs [1]. Poultry nutrition differs considerably from that of other livestock, which is determined by the specific anatomy of the gastrointestinal tract [2]. The digestive system of birds is short which causes that an average daily feed intake is low. Therefore, the feed must be varied and contain all the necessary nutrients. Even a short-term feeding a diet that does not cover nutrient requirements impairs growth and development of young birds [3], while in older birds decreases or inhibits production [4, 5] and contributes to worsening of the health status [6], [7], [8], [9], [10], [11].

Protein, energy, fat, fiber, minerals, vitamins, and water are of basic importance for poultry nutrition and their content in feeds must cover the requirement that differ depending on the bird's age and species. In general, feed protein must be of good value including the content of essential amino acids. Among them lysine, methionine, cysteine, threonine, and tryptophan are the limiting ones. Nowadays, plant feeds supplemented with crystalline amino acids are the main source of amino acids. In poultry diets, the metabolizable energy to protein ratio is very important. An appropriate energy concentration in diets is ensured by carbohydrates, fat, and protein. Dietary fiber is a feed constituent which importance in poultry nutrition has increased considerably in recent years [12]. The reason for that is the increasing knowledge about the composition and activity of the intestinal microbiota which produces numerous bioactive compounds during fiber fermentation [13], [14], [15], [16], [17], [18]. Ducks and geese better utilize dietary fiber than chickens, and geese better than ducks. This is because of that geese have an efficient and powerful proventriculus and gizzard and an effective microbial fermentation occur in their large intestine [19].

Minerals and vitamins are necessary for the regulation of metabolism and ensure a proper development of young organisms and birds' productivity [20, 21]. Water is another essential constituent in poultry nutrition. Requirement for water depends on: species, body weight, age, physiological state, productivity, external temperature, and rearing system [22].

The main ingredient of poultry feeds are cereal grains, i.e. wheat and maize, which predominantly constitute an energy source because their protein content is insufficient for birds. Because of that cereals cannot be the only feed for poultry and must be combined with protein sources such as soybean or rapeseed meal, legume seeds or protein concentrates. Animal protein sources are also available for poultry nutrition and include fish meal, blood meal or feather meal. Forages are mainly used in ducks and geese feeding but their use depend on the production system [23, 24]. Poultry feeds also contain fat sources such as plant oils or animal fat, mineral-vitamin mixes, and a wide range of feed additives including enzymes, pre- and probiotics, antioxidants, etc. Usually, all these ingredients are included in one balanced feed, which composition is adjusted to the bird species, type of production, growth phase, metabolic rate, as well as anatomy and physiology of the digestive tract [25], [26], [27], [28], [29]. This is the most convenient method of poultry feeding ensuring the coverage of nutrient requirement and high productivity.

Despite birds' requirement for nutrients and chemical composition of feeds are well known, nutrition must face many problems. One of the most important issue is to find alternatives to antibiotic growth promoters which will ensure intestinal microbiota balance without the risk of development of antibiotic resistance in bacteria species [30]. Another one is the decreasing consumer acceptance for products originating from birds fed diets containing the genetically modified crops. Owing to consumer concerns as well as increasing prices of soybean meal, alternative protein sources must be taken into consideration [27, 31, 32]. However, the use of diets without or with reduced content of soybean meal requires studies on the effect on growth performance, gastrointestinal tract physiology and production profitability. Modern poultry nutrition also must ensure birds' welfare as well as reduction of the negative impact of production on the environment. Improvement of nitrogen and phosphorus utilization by birds and reduction of emission of ammonia, hydrogen sulfide, and other odorous compounds are of particular importance [33], [34], [35]. Nowadays, climate warming and the resulting heat stress are becoming a growing problem [28]. Therefore, modern approach in poultry nutrition must include solutions for alleviation of the negative impact of the heat stress on birds' physiology and productivity. There are many effective feed additives that may counteract and prevent some of these problems [36]. Also, plant breeders have obtained modern cultivars of legumes that may partially replace soybean meal in poultry diets.

In this chapter, anatomical and physiological bases of poultry nutrition, recent advances in the field of intestinal microbiota research, feed characteristics, and the most important directions of feeding of different bird species are given.

1.2 Gastrointestinal tract physiology in poultry

The digestive tract of poultry is important in converting the feed that is eaten into the nutrients which are necessary for growth, maintenance, and reproduction. Feed is broken in the body by mechanical and chemical processes. In many animals, the mechanical action involves chewing but due to the fact that birds do not have teeth, their bodies use other mechanical action. The chemical action involves digestive enzymes and fluids which are released from various parts of the digestive system. After being released from feed during digestion, nutrients are absorbed and distributed throughout the bird's body.

The digestive tract of chickens and most other birds consists of several sections which differ in morphological structure and function. The first part is the mouth, which, as compared to the mammalian organ, has no lips, cheeks, teeth, masseter muscles, and jaws but there is an organ called the beak. The hen's beak is slightly curved and pointed at the apex of its upper part. It is a prehensile organ. The hen's palate is the arch of the beak cavity and is not completely separate from the nasal cavity. The gap in it ensures communication between the beak and the nasal cavity. The beak cavity in...