Influence of autonomous regulation type on the connective tissue content in the muscular membrane of the chickens’ small intestine

The relationship between the small intestine's muscular membrane structure of chickens and the autonomous regulation type was investigated. Based on electrocardiographic and variational pulsometric studies, adult laying hens of the Isa-Brown breed were divided into two groups: sympathotonic (ST) and sympatho-normotonic (ST-NT). The volume of individual layers and the entire muscle membrane, as well as the volume of connective tissue fibers located in it, was determined in the small intestine of the hens. In general, the relationship between morphological parameters and the autonomous regulation type is similar throughout the whole intestine, but it has certain peculiarities in different intestine parts. An increase in the volume of both the circumferential and longitudinal layers of the intestinal muscular membrane accompanies an increase in sympathetic tonus. This pattern is typical for both groups. The ratio between these layers varies along the intestinal wall: the share of the longitudinal layer increases while that of the circumferential layer decreases. Accordingly, the average volume of the entire small intestine's muscular membrane in ST and ST-NT chickens differs by 590.6 mm3, and the total volume by 1771.7 mm3. Increased sympathetic tonus also contributes to a more significant number of collagen fibers in the circular layer of the muscle membrane. In the average values of the small intestine, its superiority over the longitudinal layer is 5.6 % in ST chickens and 3.4 % in ST-NT chickens. Regarding absolute values of elastic fiber volume, no group of birds has a complete advantage along the small intestine. However, the average values of this section are still dominated by ST chickens, which outnumber the other group by 15.3 mm3 in the circumferential layer and by 11.7 mm3 in the longitudinal layer of the muscle membrane. Birds with persistent sympathotonia also have more collagen fibers per 1 mm3 muscle membrane. Regarding average small intestine parameters, ST-NT chickens demonstrate a lower value (0.005 mm3). However, regarding the number of elastic fibers alone, ST-NT chickens already occupy a dominant position, and the difference between the two groups decreases to 0.004 mm3. The established muscle membrane's morphological features indicate its plasticity in adapting the intestinal wall to the autonomous regulation peculiarities.