The current study described the developmental sequence of the ventriculus of the post-hatching Muscovy ducks of both sexes ranging from 1-60 days old, by using gross-histomorphometic measurements and by using light microscope, scanning electron microscope and transmission electron microscope. The ventriculus was extended from the level of the 4th intercostal space to terminate behind the last rib at variable distances dependent on the age of the duck. The statistical analysis revealed that the length of the ventriculus from that of the stomach was decreased by the advancement of the age, while the weight was increased. At all developmental age-stages, the cuticula gastrica was composed of two layers; vertical rods and horizontal matrix. The vertical rods projected slightly as dentate processes beyond the surface of the mucosa at 30-60dys old. The type of the gizzard gland was different according to the age; it was simple tubular type lining by one type of cells (chief cells) at 1-15 days old, but were compound-branched type lining by two types of cells; chief and basal cells at 30-60 days old. By semithin sections, the secretory basophilic granules within the cells lining of the tubular glands were increased by ageing. Transmission electron microscopy exhibited that the chief cells had numerous large sizes electron dense and electron lucent secretory granules. In conclusion, there are wide variations in the morphometrical analysis and the structure of the ventriculus at the developmental age-stages of the duck.

The lack of proofreading activity of the viral polymerase and the segmented nature of the influenza A virus (IAV) genome are responsible for the genetic diversity of IAVs and for their ability to adapt to a new host. We tried to adapt avian IAV (avIAV) to the pig by serial passages in vivo and assessed the occurrence of point mutations and their influence on viral fitness in the pig’s body. A total of 25 in vivo avIAV passages of the A/duck/Bavaria/77 strain were performed by inoculation of 50 piglets, and after predetermined numbers of passages 20 uninoculated piglets were exposed to the virus through contact with inoculated animals. Clinical signs of swine influenza were assessed daily. Nasal swabs and lung tissue were used to detect IAV RNA by real-time RT-PCR and isolates from selected passages were sequenced. Apart from a rise in rectal temperature and a sporadic cough, no typical clinical signs were observed in infected pigs. The original strain required 20 passages to improve its replication ability noticeably. A total of 29 amino-acid substitutions were identified. Eighteen of them were detected in the first sequenced isolate, of which 16 were also in all other analysed strains. Additional mutations were detected with more passages. One substitution, threonine (T) 135 to serine (S) in neuraminidase (NA), was only detected in an IAV isolate from a contact-exposed piglet. Passaging 25 times allowed us to obtain a partially swine-adapted IAV. The improvement in isolate replication ability was most likely related to S654 to glycine (G) substitution in the basic protein (PB) 1 as well as to aspartic acid (D) 701 to asparagine (N) and arginine (R) 477 to G in PB2, glutamic acid (E) 204 to D and G239E in haemagglutinin and T135S in NA.