In vertebrates and invertebrates, morphological and functional features of gastrointestinal (GI) tracts generally reflect food chemistry, such as content of carbohydrates, proteins, fats, and material(s) refractory to rapid digestion (e.g., cellulose). The expression of digestive enzymes and nutrient transporters approximately matches the dietary load of their respective substrates, with relatively modest excess capacity. Mechanisms explaining differences in hydrolase activity between populations and species include gene copy number variations and single-nucleotide polymorphisms. Transcriptional and posttranscriptional adjustments mediate phenotypic changes in the expression of hydrolases and transporters in response to dietary signals. Many species respond to higher food intake by flexibly increasing digestive compartment size. Fermentative processes by symbiotic microorganisms are important for cellulose degradation but are relatively slow, so animals that rely on those processes typically possess special enlarged compartment(s) to maintain a microbiota and other GI structures that slow digesta flow. The taxon richness of the gut microbiota, usually identified by 16S rRNA gene sequencing, is typically an order of magnitude greater in vertebrates than invertebrates, and the interspecific variation in microbial composition is strongly influenced by diet. Many of the nutrient transporters are orthologous across different animal phyla, though functional details may vary (e.g., glucose and amino acid transport with K+ rather than Na+ as a counter ion). Paracellular absorption is important in many birds. Natural toxins are ubiquitous in foods and may influence key features such as digesta transit, enzymatic breakdown, microbial fermentation, and absorption.

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Comparative digestive physiology.

Omega-3 (ω-3) and omega-6 (ω-6) fatty acids are important components of cell membranes. They are essential for health and normal physiological functioning of humans. Not all fatty acids can be produced endogenously owing to the absence of certain desaturases; however, they are required in a ratio that is not naturally achieved by the standard diet of industrialized nations. Poultry products have become the primary source of long-chain polyunsaturated fatty acids (LC-PUFA), with one of the most effective solutions being to increase the accretion of PUFAs in chicken products via the adjustment of fatty acids in poultry diets. Several studies have reported the favorable effects of ω-3 PUFA on bone strength, bone mineral content and density, and semen quality. However, other studies concluded negative effects of LC-PUFA on meat quality and palatability, and acceptability by consumers. The present review discussed the practical application of ω-3 and ω-6 fatty acids in poultry diets, and studied the critical effects of these fatty acids on productive performance, blood biochemistry, immunity, carcass traits, bone traits, egg and meat quality, and semen quality in poultry. Future studies are required to determine how poultry products can be produced with higher contents of PUFAs and favorable fatty acid composition, at low cost and without negative effects on palatability and quality.

Omega-3 and Omega-6 Fatty Acids in Poultry Nutrition: Effect on Production Performance and Health.

This review provides a comprehensive overview of the vascularization of the avian growth plate and its subsequent role in the pathogenesis of bacterial chondronecrosis with osteomyelitis (BCO, femoral head necrosis). BCO sporadically causes high incidences of lameness in rapidly growing broiler (meat-type) chickens. BCO is believed to be initiated by micro-trauma to poorly mineralized columns of cartilage cells in the proximal growth plates of the leg bones, followed by colonization by hematogenously distributed opportunistic bacteria. Inadequate blood flow to the growth plate, vascular occlusion, and structural limitations of the microvasculature all have been implicated in the pathogenesis of BCO. Treatment strategies have been difficult to investigate because under normal conditions the incidence of BCO typically is low and sporadic. Rearing broilers on wire flooring triggers the spontaneous development of high incidences of lameness attributable to pathognomonic BCO lesions. Wire flooring imposes persistent footing instability and is thought to accelerate the development of BCO by amplifying the torque and shear stress imposed on susceptible leg joints. Wire flooring per se also constitutes a significant chronic stressor that promotes bacterial proliferation attributed to stress-mediated immunosuppression. Indeed, dexamethasone-mediated immunosuppression causes broilers to develop lameness primarily associated with avascular necrosis and BCO. Prophylactic probiotic administration consistently reduces the incidence of lameness in broilers reared on wire flooring, presumably by reducing bacterial translocation from the gastrointestinal tract that likely contributes to hematogenous infection of the leg bones. The pathogenesis of BCO in broilers is directly relevant to osteomyelitis in growing children, as well as to avascular femoral head necrosis in adults. Our new model for reliably triggering spontaneous osteomyelitis in large numbers of animals represents an important opportunity to conduct translational research focused on developing effective prophylactic and therapeutic treatments.

Bone circulatory disturbances in the development of spontaneous bacterial chondronecrosis with osteomyelitis: a translational model for the pathogenesis of femoral head necrosis.

Bacterial chondronecrosis with osteomyelitis and lameness in broilers: a review

SUMMARY Nutrient deposits in the fertile egg affect broiler embryo development and hatchling quality Although the fertile egg has a defined nutrient composition, the rate and mechanism of absorption of these nutrients by the yolk sac membrane (YSM) and by the embryonic intestine are largely unknown Current research by our group is focused on the levels of the macronutrients (fat, protein, water, and carbohydrates) and micronutrients (P, Ca, Fe, Zn, Cu, and Mn) in the yolk and the albumen, and their utilization from the yolk sac during incubation In addition, the physiological, cellular, and molecular mechanisms by which the developing embryo derives its nutrition via the YSM are investigated Different limitations in yolk mineral and fat availability and in their utilization by the embryo during incubation have been observed These findings contribute to a better understanding of the ability and capacity of the YSM to digest and transport nutrients; provide insight into the role of the YSM as similar to that of the intestine and, to some extent, to that of the liver; and lead to new perspectives on the role of the yolk sac in supplying nutrients to the embryo for its optimal development

R. Yair

Papers

Content and uptake of minerals in the yolk of broiler embryos during incubation and effect of nutrient enrichment

Nutritional limitations during poultry embryonic development

The chick embryo yolk sac membrane expresses nutrient transporter and digestive enzyme genes

In ovo feeding with minerals and vitamin D3 improves bone properties in hatchlings and mature broilers

Bone characteristics of late-term embryonic and hatchling broilers: Bone development under extreme growth rate