Unilateral relationship of embryos and the corpus luteum in cattle

Abstract

The unilateral relationship between embryo and corpus luteum was studied in two experiments in Holstein heifers. Two fertilized ova were inserted into one uterine horn of recipient heifers on Day 6 after estrus. Recipients were given progesterone from Day 13 through Day 23 and were necropsied on Day 24 (18 days after ova transfer). Corpora lutea were weighed and classified as maintained or regressed. In Exp. 1, the uterine horns were separated and the fertilized ova were inserted ipsilateral (group 1, 5 heifers) or contralateral (group 2, 5 heifers) to the CL. Nine of 10 heifers were pregnant at necropsy. Mean CL weight for group 1 (3725 mg) was greater (P<0.01) than that for group 2 (1300 mg). Results indicated that in heifers with a surgically isolated uterine horn a unilateral utero-ovarian mechanism was involved in maintenance of the CL during early pregnancy. Experiment 2 was designed to determine if embryos inserted into the uterine horn contralateral to the CL in uterine-intact heifers would maintain the CL and, if so, whether the luteotropic message passed from gravid to nongravid side through the uterine body and horns or through the intercornual area. Recipient heifers were randomized into 4 groups (n=4): 1) uterine-intact controls; 2) ipsilateral horn transected, intercornual ligament intact; 3) uterine horns intact, intercornual ligament severed; 4) ipsilateral horn and intercornual ligament severed. Mean CL weight was smaller (P<0.05) in group 1 (2900 mg), group 2 (1405 mg) and group 4 (578 mg) than in group 3 (4848 mg). There was a significant difference between groups 1 and 3 although the CL in all heifers in both groups were classified as maintained. Mean CL weight was not significantly different between groups 2 and 4. Results indicated that embryos transferred to the contralateral horn were capable of maintaining the CL if the uterine horns were not separated. The passage of the luteotropic message from gravid to nongravid side was exerted through the uterine body and horns rather than through the intercornual area and is most likely attributable to the growth of embryonic membranes into the nongravid horn.