Induction and Formation of Accessory Corpus Luteum after Artificial Insemination (AI) Might Increase Pregnancy Rate per AI in Heat Stressed Dairy Cows

Abstract

The present study aimed to evaluate whether the induction and the formation of an accessory corpus luteum (CL) after AI might increase the pregnancy per AI (P/AI) in heat stressed dairy cows. Starting at d 50±3 post-partum, 113 lactating Holstein cows from one commercial herd during summer were scored for body condition, blood sampled and examined by ultrasound. Those bearing a CL>25mm and progesterone (P4) level>2ng/mL were synchronized using a double PGF2α injection given 12 h apart and AI-ed at detected estrus. In total 18 cows, there were not any signs of estrus (n=10) nor a P4 level <2ng/mL at the time of enrolment (n=8) and therefore they were excluded from the study, leading to 95 cows finally enrolled.. At d5 post-AI, cows were randomly allocated into 2 groups: control group (CON, n=45) without any additional treatment, and treatment group (GnRH, n=50), treated with 0.008 mg Buserelin – a GnRH agonist. Blood sampling and ultrasound examination were done at d5, d14 and at d21 after AI, whereas the pregnancy diagnosis was done at d21 and d30 after AI. Average daily temperature and relative humidity values were used to calculate the temperature-humidity index (THI). The average THI during the experiment was 79.5±0.6. At d5, no differences were observed neither between the number of the CL nor between the P4 level in both groups. At d14 and d21, 82% of the GnRH-treated cows had more than one CL versus 0% of the CON cows. Both at d14 and 21, GnRH-treated cows had higher P4 levels compared to the CON cows (p<0.05). In addition, P/AI were higher in the GnRH group than in the CON group (65% vs. 48.3%, p<0.05), whereas late embryonic losses were higher in CON in comparison to GnRH cows (10.6 vs. 4%, respectively). The BCS at the moment of insemination did not affect P/AI (p>0.05). In conclusion, the induction of an accessory CL at d 5 after AI might increase P/AI in heat stressed dairy cows.

Effect of increased serum progesterone on luteal morphology and function, pregnancy, and gestational loss in Nelore cows

“…More recent experiments based on P4 supplementation after AI had satisfactory results with GnRH, hCG (Akhtar et al, 2018; Stojanov et al, 2020), or a long‐acting P4 (Couto et al, 2019; Pugliesi et al, 2016). In contrast, some studies evaluating the effect of increased plasma P4 levels on fertility did not reveal improved pregnancy rates, despite the use of higher concentrations of P4 in the supplemented groups.…”

“…Thus, an increase in the serum concentration of P4 can be beneficial to the uterine environment, affecting the reproductive efficiency of beef herds in timed artificial insemination (TAI) programs. Strategies that promote increased P4 concentration in early dioestrus can increase pregnancy rates and decrease gestational loss (GL) (Couto et al, 2019; Pugliesi et al, 2016; Stojanov et al, 2020).…”

“…Previous studies have evaluated the effect of P4 supplementation on dioestrus, either via exogenous supplementation or the use of luteotropic agents, and reported satisfactory results with increased pregnancy rates (Akhtar et al, 2018; Couto et al, 2019; Junior et al, 2017; Mehni et al, 2012; Stojanov et al, 2020) and decreased embryonic loss (Beltman et al, 2009; Couto et al, 2019; Junior et al, 2017).…”

“…P4 supplementation after insemination and its possible effects on vascularization and luteal functions in cattle have not been investigated yet. Studies conducted with dairy and beef cows did not reveal whether supplementation would be harmful to the viability of the CL (Couto et al, 2019; Souza et al, 2013; Stojanov et al, 2020). Further, supplementation had no effects on the size and volume of the CL (Beltman et al, 2009; Monteiro et al, 2015; Nascimento et al, 2013).…”

Efficiency of Two Protocols of Resynchronization of Estrus and Ovulation in High-Producing Dairy Cows at Peak Lactation

“…High P4 (>2 ng/mL) concentrations in dairy cows immediately before PGF 2α is administered [28] and its low levels at AI [29] are crucial for maximizing the following P/AI in TAI programs [30]. In both groups, cows with a good ovulatory response to PGF 2α , which was refl ected in low P4 values at the time of GnRH2 application (Table 1), had higher P/AI.…”