Embryological development of the spiral loop of the bovine ascending colon.

The spiral colon is formed as the result of a lengthening and coiling of the midgut ascending limb. The literature reports two arguments that explain the details of such a development: the first argues that the spiral loop is formed to the left of the mesentery (Asari et al. Jpn J Vet Sci 47, 1985; McGeady et al. Veterinary Embriology, 2006; Noden and De Lahunta, Embriologia degli animali domestici, 1991), while the second to the right of it (Barone, Anatomia comparata dei mammiferi domestici, 2003). The purpose of this study was to clarified this aspect and identified the point at which the spiral loop adheres to the mesentery. Twenty-five Holstein bovine foetuses between 2.7 and 23 cm crown-rump length (CRL) were used in this study. Between 2.7 and 4.5 cm CRL (45-55 days of gestation) the ascending limb of the midgut occupies the umbilical cord. Between 4.5 and 8 cm (55-67 days) the first evidence of looping of the spiral loop is seen on the right side of the mesentery. Subsequently, the spiral loop, passing caudal to the mesentery, moves to the left side and concludes its looping forming a coil. Between 8 and 12 cm (67-85 days) the spiral loop adheres to the mesentery. Our observations, therefore, are in a condition intermediate to the two theses previously exposed. The identification of the moment in which the spiral loop adheres closely to the mesentery is particularly important in understanding the abnormalities of the colon.