186 Vascular and morphological features of the corpus luteum 7 to 16 days post-AI and application of OvSynch and OvSynch + P4 protocols in dairy cows

The fertility of dairy cows has declined in the past three decades worldwide. One of the reported changes is increased liver blood flow, resulting in altered steroid metabolism and low efficiency of oestrus detection, which has motivated professionals to use oestrus synchronisation programs in a generalised way. OvSynch is a widely accepted oestrus synchronisation protocol for improving fertility. Although some reported weaknesses of the OvSynch protocol include inadequate luteolysis, low body condition score, and reduced follicular activity, they should be evaluated for changes in the synchronisation protocols to improve the pregnancy rate. The aim of this work was to evaluate the vascular and morphological features of the corpus luteum 7 to 16 days post-AI and application of OvSynch and OvSynch + Progesterone (P4) protocols in dairy cows. 10 dairy cows were selected at 34 to 35 days of lactation (postpartum), body condition (2 to 2.75; scale 1–5) and without reproductive pathologies. They were randomised to the OvSynch conventional and OvSynch + P4 protocols that include a progesterone implant (0.5 g) for 7 days (OvSynch protocol: gonadotrophin-releasing hormone [GnRH] on Day 0, PGFalpha on Days 7 and 8, GnRH 56 h after the first dose of PGFalpha). At Days 7 and 16 after fixed-time artificial insemination, cow ovaries were scanned for corpus luteum vascularity and morphology using ultrasound (MyLab™OneVET, Esaote Vet) equipped with a linear array rectal transducer in B-mode (6.0 MHz, 80% gain) and colour Doppler mode (6.6 MHz, 2.5 kHz pulse repetition frequency, 17.8 cm/s frame rate). The morphology of the corpus luteum (echotexture) size was measured in mm, while the vascularity was subjectively evaluated and classified into 4 degrees: 1 low; 2 medium; 3 intermediate; 4 high. Numerical data characterising the corpus luteum were subjected to descriptive statistical analysis (mean and standard deviation). The variables of the groups were compared with the independent Student’s t-test. P-values < 0.05 were considered statistically significant. The results indicate that the cows synchronised with OvSynch + P4 versus OvSynch conventional showed a numerically greater size (19.5 vs 15.5 mm) and degree of vascularity (1.3 vs 0.5) of the corpus luteum by Day 7 post-AI, but did not show significant differences. At Day 16, the cows showed a corpus luteum with increased size (22.5 vs 17.3 mm) and a reduction in the degree of vascularity (1.0 vs 0.67); however, the cows who were diagnosed as pregnant on Day 28 post-AI showed a higher degree of vascularity (between 2 to 2.5) on Day 16 of the measurement. In conclusion, the vascularity and morphological features of the corpus luteum 7 and 16 days post-AI showed the best characteristics after the application of OvSynch + P4 protocols.

This research was supported by Unidad Experimental de Zootecnia, Renato Zepilli.