The morphology and postnatal development of isthmus region of the oviduct in the Kuttanad duck was studied using 78 ducklings from day-old to 24 weeks in 13 different age groups. Isthmus was not differentiated grossly from the magnum and uterus up to 10th week of age in Kuttanad duck. Differentiation of the isthmus region occurred at the same time as that of more cranial segments of the oviduct, that is, at 12th week of age. Isthmus showed a small diameter when compared to the magnum, since the time of its differentiation at 12th week to 24th week of age. A spurt in growth of magnum occurred between 18 to 20 weeks of age, when egg laying started in these birds. In differentiated oviduct, similar to magnum, the weight, length and width of the isthmus region showed highly significant positive correlation with the age and weight and length of oviduct but no significant correlation with the body weight. The present study thus indicated presence of a longer isthmus region in native Kuttanad ducks similar to that of Japanese quail and Nothura spotted quail which might explain thicker shell membranes in these birds.
Lekshmi Priya Menon (Tue,) studied this question.