Estrous response and conception rate in postpartum Bos taurus-Bos indicus cows, treated with bovine somatotropin in an ovulation induction program with progestogens and eCG

Abstract

Bovine somatotropin (bST) injection was administered at the beginning of the ovulation induction with progesterone and eCG, and a second one during insemination to prove if it increased estrous response and conception rate (CR) in postpartum beef cows. A hundred and seventy four cows (Bos taurus-Bos indicus) of 60 to 100 days postpartum, with offspring and body con­dition of 2 to 2.5 were used. A progesterone-releasing intravaginal device (CIDR) was inserted to all females for 9 days and, while removing it, PGF2α was injected. Cows were randomly assigned to the following treatments: eCG (n = 44), received 400 IU of eCG at the moment CIDR was removed; bST (n = 44), received 500 mg of bST when CIDR was inserted and 500 mg of bST during insemination; bST-eCG (n = 44), received 500 mg of bST when CIDR was inserted and 400 IU of eCG while removing it; and 500 mg of bST during insemination; control (n = 42), only received the CIDR. Progesterone concentrations were assessed before the insertion of CIDR. IGF-I serum concentrations were determined in seven cows of each group. At the beginning of the experiment, 93% of the cows were in anoestrus. The rate of cows that showed estrus was similar (P > 0.05) between treatments [eCG (36.4%; bST (45.4%); eCG-bST (52.2%); control (40.4%)]. The CR was not different (P > 0.05) be­tween treatments [eCG (31.2%); bST (15%); eCG-bST (34.7%); control (40%)]. Cows treated with bST had higher IGF-I con­centrations than control cows. It is concluded that the injection of bST at the beginning of the ovulation induction with proges­terone and eCG, and a second one during insemination does not improve estrous response or fertility in postpartum beef cows.