137 MACROSCOPIC AND MICROSCOPIC CHARACTERISTICS OF THE FEMALE LLAMA (LAMA GLAMA) FETAL, INFANTILE, AND ADULT GENITAL TRACTS

Abstract

The higher incidence of the left uterine horn gestations that occur in llamas (Lama glama) might be due to anatomical differences between the uterine horns. A study of the macro- and micro-anatomy of the female llama genital tract was conducted to determine possible differences between the left and the right uterine horns. Female genital tracts were obtained at a local slaughterhouse and immediately kept in a fixing solution. A total of 74 genital tracts were inspected grossly and/or by translumination after fixation (54 fetuses, 2 infantiles, 1 and 30 days old, and 18 adults, 3 to 8 years old) to determine gross anatomy. Fetal genital tracts were arranged, according to the Crown-Ramp lengths (C-R), into 6 groups: Group 1, 25.0-29.5 cm (n = 3); Group 2, 30.0-39.5 cm (n = 18); Group 3, 40.0-49.5 cm (n = 18); Group 4, 52.0-59.6 cm (n = 9); Group 5, 62.7-63.5 cm (n = 2); and Group 6, 70.6-78.9 cm (n = 4). Length of the uterine septum and the outer length (flexible ruler) and diameter (caliper) of the uterine horns, body of the uterus, and cervix were taken. Uterine luminal diameter was taken at 3 previously selected places. Length and diameter of the left and right uterine horns were compared by differences of means for paired observations and used to prepare regression curves of length and diameter growth in relation to C-R length. Seventeen of the 54 fetal genital tracts (two from Group 5 and three from each of the other groups), both infantile tracts, and 11 of the 18 adult tracts were used to determine microscopic characteristics. Histological preparations of tissue from 3 previously selected areas, (3 sections/area) of the left and right uterine horns, and from 1 area of the uterine septum and cervix, were prepared. Thickness samples of the uterine wall, endometrium, and myometrium plus perimetrium of the left and right uterine horns were measured under the microscope using a micrometer and were compared by differences of means for paired observations in relation to C-R length. Results indicated that, on an anatomical basis, the outer lengths and luminal diameters of the left uterine horn, from early fetal stages to adulthood, were greater than the right uterine horn (P ≤ 0.05). The special anatomical disposition of the uterine septum appeared to restrict the diameter of the lumen of the right horn. No microscopic differences were detected between horns. Additionally, uterine glandular development was found in fetal genital tracts at an early age (from C-R length, 34.5 cm and onward) and no differences were found either between left and right uterine horns or between fetal and adult genital tracts. In summary, both uterine horns, on a microscopic basis, were not different and appeared to be competent to carry out physiological events such as gestation. On a gross anatomical basis, the left uterine horn presented a greater luminal diameter than the right uterine horn. The greater space that the left uterine horn offers and the peculiar disposition of the uterine septum appear to contribute to the higher incidence of left uterine horn gestations.