Abstract

VELAZQUEZ ROSAS, Linda Esther; FREGOSO AGUAYO, Carlos; LOPEZ ORDAZ, Reyes  and  HERNANDEZ CERON, Joel. 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. Vet. Méx [online]. 2011, vol.42, n.3, pp.245-251. ISSN 0301-5092.

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, PGF2a 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.

Keywords : bST; conception rate; beef cattle; ovulation.

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