Progesterone concentration, pregnancy and calving rate in Simmental dairy cows after oestrus synchronisation and hCG treatment during the early luteal phase

Abstract

Early embryonic development may be negatively affected by insufficient progesterone (P4) production. Therefore, the aim of our study was to increase P4 by gonadotropin-releasing hormone (GnRH) and/or human chorionic gonadotropin (hCG) treatments after inducing oestrus by prostaglandin (PG) treatment. Lactating Simmental dairy cows (n = 110), between 1 to 5 lactations, with an average milk production of 6,500 1/305 days, at 40-80 days postpartum were used and grouped as follows: (1) PG + GnRH treatment at AI (GnRH group), (2) PG + hCG treatment at day 7 after AI (hCG group), (3) PG + GnRH at AI + hCG treatment at day 7 after AI (GnRH/hCG group), and (4) spontaneous oestrus (C: control group). All animals were double inseminated (at the time of oestrus detection and 12 ± 2 h thereafter). Blood serum and milk samples were collected at the day of observed oestrus (day 0), and 14, 21 and 28 days after AI. Serum P4 was determined using a commercial radioimmunoassay (RIA) test (INEP, Zemun), and milk P4 was determined using enzyme-linked immunoassay (ELISA) test (NIV Novi Sad). Pregnancy status was confirmed by ultrasonography between days 28 and 35 after AI. Differences of serum or milk P4 medians, pregnancy (and calving) rate were determined using Dunn's Multiple Comparison Tests and Z test, respectively. Serum P4 medians were significantly higher at days 14, 21 and 28 after AI in the hCG-treated animals, indicating increased luteal activity, with a similar tendency in whole milk P4 values. Treatment with hCG during the early luteal phase significantly contributed to the maintenance of gestation at days 28-35 after AI, and also increased the calving rate in Simmental dairy cows.

Two melatonin treatments improve the conception rate after fixed‐time artificial insemination in beef heifers following synchronisation of oestrous cycles using the CoSynch‐56 protocol

“…We found administration of hCG after AI has not consistently increased conception rates to AI. Although, previous reports indicate that supplementation of hCG 7 days after AI is beneficial for early CL development, effectively maintaining the pregnancies and leading to an increase in the calving rate and reducing embryo loss 25 . The present results showed that injecting hCG at 5 days after AI could not significantly improve the conception rate even though serum P4 concentration on both days 10 and 45 was greater in the MT + hCG group than in the CTR group 41 .…”

“…Administration of human chorionic gonadotropin (hCG) on day 5 after oestrus induces the formation of an accessory corpus luteum (CL) while increasing the concentration of P4 from day 7 24 . Supplementation of hCG after AI is beneficial to early CL development and effectively maintains the pregnancy, increasing the calving rate and reducing embryonic loss 25 . Despite the potential benefits of supplementing with melatonin during AI, its effects on fertility of beef cattle inseminated at a synchronised oestrus have not yet been studied.…”

Effects of GnRH or hCG on day 11 after artificial insemination in cows luteal activity

“…Other studies have shown that administration of natural sequence GnRH, GnRH agonists or hCG after AI can stimulate CL function which induces accessory CL formation, increases progesterone concentration, and reduces oestradiol production with a consequent positive effect on embryonic survival (Thatcher et al, 2003). Administration of GnRH, a GnRH agonist or hCG after AI at specific times, coincident with the presence of the dominant follicle of the first and second follicular waves, may stimulate CL function, induce accessory CL formation, increase progesterone concentration (Schmitt et al, 1996a, Stevenson et al, 2007 and reduce oestrogen production with a consequent positive effect on pregnancy rate or embryo survival (Thatcher et al, 2003;Šuluburić et al, 2017). Several studies have investigated the effects of GnRH administered during mid-estrous cycle (day 12, 13 or 14 after AI) (Szenci et al, 2006;Lopez-Gatius et al, 2006).…”