First Service Pregnancy Rates Following Post-AI Use of hCG in Ovsynch and Heatsynch Programmes in Lactating Dairy Cows

Abstract

Lactating dairy cows (n = 667) at random stages of the oestrous cycle were assigned to either ovsynch (O, n = 228), heatsynch (H, n = 252) or control (C, n = 187) groups. Cows in O and H groups received 100 microg of GnRH agonist, i.m. (day 0) starting at 44 +/- 3 days in milk (DIM), and 500 microg of cloprostenol, i.m. (day 7). In O group, cows received 100 microg of GnRH (day 9) and were artificially inseminated without oestrus detection 16-20 h later. In H group, cows received 1 mg oestradiol benzoate (EB) i.m., 24 h after the cloprostenol injection and were artificially inseminated without oestrus detection 48-52 h after the EB injection. Cows in C group were inseminated at natural oestrus. On the day of artificial insemination (AI), cows in all groups were assigned to subgroups as follows: human Chorionic Gonadotrophin (O-hCG) (n = 112), O-saline (n = 116), H-hCG (n = 123), H-saline (n = 129), C-hCG (n = 94) and C-saline (n = 93) subgroups. Cows in hCG and saline subgroups received 3000 IU hCG i.m. and or 10 ml saline at day 5 post-AI (day 15), respectively. Pregnancy status was assessed by palpation per rectum at days 40 to 45 after AI. The logistic regression model using just main effects of season (summer and winter), parity (primiparous and pluriparous), method(1) (O, H and C) and method(2) (hCG and saline) showed that all factors, except method(1), were significant. Significant effects of season (p < 0.01), hCG and parity (p < 0.01), and a trend of parity and season (p < 0.1) were detected. A clear negative effect of warm period on first service pregnancy rate was noted (p < 0.01). The pregnancy rate was the lowest in the H protocol during warm period (p < 0.05). Treatment with hCG 5 days after AI significantly improved pregnancy rates in those cows that were treated with the H protocol compared with saline treatments (41.5% vs 24.8%; p < 0.01). O and H were more effective in primiparous than in pluriparous cows (46.1% vs 29.9%; p < 0.1 and 43.6% vs 24.6%; p < 0.01). First service pregnancy rates were higher in primiparous hCG-treated than in pluriparous hCG-treated cows (57.9% vs 32.3%; p < 0.01). The pregnancy rate was higher for the hCG-treated cows compared with saline-treated cows during warm period (37.9% vs 23.6%; p < 0.001).

Reproductive physiology of the heat-stressed dairy cow: implications for fertility and assisted reproduction

“…As already discussed, ovulation failure is more frequent during periods of heat stress and administration of more active analogs of GnRH can reduce the incidence of ovulation failure (García-Ispierto et al, 2019). In another study, Shabankareh et al (2010) evaluated the summer-winter differences in P/AI at first service for cows bred at spontaneous estrus or following timed AI using either GnRH (Ovsynch) or estradiol cypionate (Heatsynch) to induce ovulation. There was no difference in P/AI (32, 30 and 30% for OvSynch, Heatsynch and spontaneous estrus) in the summer while P/AI in the winter was highest for spontaneous estrus (51%), intermediate in Ovsynch (40%) and lowest for Heatsynch (35%).…”

“…Administration of progesterone using a CIDR device from day 5 to 18 after insemination did not cause an overall increase in P/AI but there were positive effects of the treatment in cows with low body condition or postpartum uterine disorders (Friedman et al, 2012). In the study of Shabankareh et al (2010), treatment with human chorionic gonadotropin (hCG) on day 5 after insemination increased P/AI in both summer (24 vs 38% for saline and hCG) and winter (35 vs 47%). Treatment with hCG at day 5 also increased pregnancy rate in cows during summer but the effect was seen only for primiparous cows (Zolini et al, 2019).…”

Identification of inadequate maternal progesterone concentrations in nulliparous dairy heifers and treatment with human chorionic gonadotrophin

“…The majority of studies that have demonstrated a treatment benefit have been in populations of lactating cows with lower fertility (control PR of below 50 per cent); Shabankareh and others (2010) revealed a benefit of treatment with an increase in PR to first insemination from 30 per cent to 43 per cent as did Santos and others (2001) (39–46 per cent). Lactating, compared to non-lactating cattle have been shown to metabolise progesterone more rapidly as a result of increased liver blood flow (Sangsritavong and others 2002).…”

“…However, hCG administered on day 5 or 6 has resulted in variable fertility: some reporting an increase in pregnancy rate (Santos and others 2001, Shabankareh and others 2010) while others found no effect (Schmitt and others 1996b, Walker and others 2005) despite elevated peripheral blood progesterone concentrations.…”

Effects of gonadotropin-releasing hormone administration or a controlled internal drug-releasing insert after timed artificial insemination on pregnancy rates of dairy cows

“…In this regard, a number of studies were performed to increase the circulating progesterone concentration post-insemination, thereby increasing fertility in dairy cows [131635]. An accessory corpus luteum (CL) is induced by treatment with gonadotrophin-releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) at 5 or more days post-insemination [82535]. Previous studies reported that treatment with GnRH or hCG increased the circulating progesterone concentration during the luteal phase [82122].…”