The corpus luteum (CL) may develop as a compact or cavitary structure. But it is unknown whether the morpho-physiological characteristics of compact corpora lutea (CLsCom) differ from that of cavitary corpora lutea (CLsCav), neither if these characteristics are determined by type, wool producing ewes (oveja de lana - OL) versus hair ewe (oveja de pelo - OP). Therefore, in our study ovaries were collected from sacrificed ewes and 81 corpora lutea were obtained from OL and 81 from OP. The experimental design was completely randomized with a 2x2 factorial arrangement of treatments. The variables evaluated were frequency, macroscopic and microscopic morphology, and production of progesterone (P4) in vitro, in 0.1 g luteum tissue, with or without addition of 350 IU of eCG. The frequency of CLsCav was higher (p≤0.05) in OP (50.6 %) than in OL (35.8 %). The CLsCav were smaller (p≤0.05) than the CLsCom. The P4 concentration in CLsCav and CLsCom of both types, with or without eCG, was similar (p>0.05) throughout culturing. The CLsCav from OP had fewer cells per visual field (19) and were larger (25 μm) than CLsCom cells (25.6 and 15 μm; p≤0.05). Hair ewes had a higher percentage of CLsCav than wool ewes. The CLsCav were smaller than the CLCom and in vitro progesterone production of the two types of CL was similar.

El cuerpo lúteo (CL) puede desarrollarse como una estructura compacta o cavitaria. Pero no se conoce si hay diferencias en las características morfofisiológicas entre los cuerpos lúteos compactos (CLsCom) y los cuerpos lúteos cavitarios (CLsCav), ni si estas características están determinadas por el tipo, ovejas de lana (OL) versus ovejas de pelo (OP). Por lo tanto, en este estudio ovarios de ovejas se recolectaron después del sacrificio, y se obtuvieron 81 cuerpos lúteos OL y 81 OP. El diseño experimental fue completamente al azar con un arreglo factorial 2x2 de tratamientos. Las variables evaluadas fueron frecuencia, morfología macroscópica y microscópica y producción de progesterona (P4) in vitro, en 0.1 g de tejido lúteo, con o sin adición de 350 UI de eCG. La frecuencia de CLsCav fue mayor (p≤0.05) en OP (50.6 %) que en OL (35.8 %). Los CLsCav tuvieron tamaño menor (p≤0.05) que los CLsCom. La concentración de P4 durante el cultivo tanto para CLsCav como para CLsCom de OL y OP, con y sin eCG, fue similar (p>0.05). Los CLsCav de OP tuvieron menos células por campo visual (19) y tamaño mayor (25 µm) que los CLsCom (25.6 y 15 µm; p≤0.05). Los OP tuvieron porcentaje mayor de CLsCav que los OL. El tamaño de los CLsCav fue menor que el de los CLCom y la producción de progesterona in vitro fue similar entre los CLsCav y los CLCom.

The objective of this study was to evaluate pregnancy rates of recipients of different breed groups (Nellore and crossbreed), as well as the effects of size and type of the corpus luteum (CL) on plasmatic concentrations of progesterone and pregnancy rates of embryo recipients. A total of 152 heifers were synchronized with progesterone implants and on the day of embryo transfer, previously obtained by superovulation and frozen in ethylene glycol, the diameter and type of the corpus luteum (cavitary and compact) was measured and blood was collected for progesterone measurement. The pregnancy rate was 44.1%, with a diameter of corpus luteum higher in recipients that became pregnant (2.03±0.41) compared with non-pregnant ones (1.86±0.34 cm). Plasmatic concentrations of progesterone did not differ between pregnant (1.50±1.05) and non-pregnant (1.31±0.91 ng/mL) animals. The type of corpus luteum did not influence the pregnancy rates. Only Angus and crossbred Marchigiana differ among themselves in pregnancy rates (33.3 and 59.2%, respectively). The pregnancy probability was affected only by CL diameter, but not by P4 plasmatic concentration. Selection of the corpus luteum size at the time of embryo transfer is an important factor to increase pregnancy rates in recipients, and compact and cavitary corpora lutea do not influence the pregnancy rates of bovine embryo recipients. Nellore recipients have pregnancy rates that are satisfactory and comparable to crossbred (Bos taurus × Bos indicus) recipients.