Fertilization rate, early embryonic mortality, and luteal function in Brahman crossbred heifers

Abstract

A study was conducted to determine the fertilization rate, incidence of embryonic mortality by day 35, and luteal progesterone secretion (in vitro) in Brahman crossbred heifers. On hundred fifty-five virgin heifers were artificially inseminated with frozen semen from a bull of high proven fertility and allotted to the day 3, day 16, or day 35 group (day 0 = estrus). Seven empty ruptured zona pellucidae (ERZP) were recovered from five heifers in the day 3 group and the fertilization rate depended upon the classification of these structures. When the ERZP were classified as ova ovulated at a previous cycle or ova damaged in the collection process, they were not included in the calculation of the fertilization rate. However, when the ERZP were classified as ova ovulated at the immediately preceding estrus and unavailable for further embryonic development, the ERZP were included in the calculation of the fertilization rate. Consequently, the fertilization rate at day 3 postinsemination was 80% or 93% when the ERZP were included or deleted from the calculations, respectively. In the day 16 group, the percentage of heifers having an embryo was 78, and in the day 5 group the percentage pregnant was 72. When the ERZP were deleted from the calculations, the fertilization rate was high (93%), and the incidence of embryonic loss between day 3 and 35 was 21% (93%-72%) (P<.05). However, when the ERZP were included in the calculations, the fertilization rate was comparatively low (80%). In the latter case the primary loss of potential embryos occurred prior to day 3 with the embryonic loss after day 3 being only 8% (80%-72%) (P<.05). fifty-one virgin Brahman crossbred heifers were used to determine the effect of luteinizing hormone (LH), estradiol 17β (E2), or a combination thereof on progesterone secretion from dispersed luteal cells collected on day 16 postinsemination (experiment 1 and 2), day 16 postestrus (nonmated group, and day 28 postinsemination (pregnant group). In experiments 1 and 2, the relationship between extraembryonic membrane length (day 16) and progesterone secretion from homologous luteal cells was also investigated. The corpora lutea in experiment 1 were thin sliced immediately after collection and placed in iced medium; whereas, the corpora lutea in experiment 2 were placed in iced medium and were not sliced until 30 to 50 min later...