Effects of insemination timing and GnRH treatment on pregnancy rates of N’Dama cattle after estrus induction with progestin

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The aim of this clinical trial was to quantify the results of pregnancy after treat­ing trypanotolerant N’Dama female cattle (n = 168) with a progesterone-releas­ing intravaginal device (CIDR; 1.38 g of progesterone) inserted for seven days. An intramuscular (IM) prostaglandin injection (500 μg of cloprostenol) was administered two days before removal of the device. Subsequently, an IM injec­tion of 400 IU of eCG was administered when the device was removed. The animals were inseminated 48 (Group 1) and 72 hours (Group 2) after removal of CIDR. In both groups, half the animals were treated with 4.2 μg of busere­lin acetate and the other half with 1 ml of physiological saline. Four protocols were thus tested: CIDR-PG-eCG/IA48h, CIDR-PG-eCG/IA48h/GnRH+, CIDR-PG-eCG/IA72h, and CIDR-PG-eCG/IA72h/GnRH+. A pregnancy diagnosis was performed by echography 45 to 60 days after insemination. The average preg­nancy rate was 37.5%. That of the adult cows (43.2%, n = 111) was significantly (p < 0.03) higher than that of the heifers (26.3%, n = 57). The pregnancy rate observed in animals in Group 2 (48.8%) was significantly higher (p < 0.002) than that observed in animals in Group 1 (26.2%). The physiological condition and injection of GnRH at the time of insemination had no significant impact on the pregnancy rate. The hormonal protocol using CIDR-PG-eCG (400 IU) and a timed artificial insemination 72 hours later improved the pregnancy rates in N’Dama females.