Pharmacological manipulation of the estrous cycle in Nellore cows: I - Effect of doses of PGF2α for luteolysis on days 5 and 7 of the estrous cycle. II - Effect of replacement of GNRH by EB, in the 5Co-Synch program, at estrus detection and distribution, at ovulation rate and pregnancy rate

Author(s)

Marcos Vinicius de Castro Ferraz Junior

• Document type: Master's Dissertation
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2013-07-02

Examining board members

Alexandre Vaz Pires; João Bosco Barreto Filho; Pietro Sampaio Baruselli

• Advisor: Alexandre Vaz Pires

Abstract

The objective of the experiment I was to evaluate the luteolysis caused by three doses of PGF2&#945; (12.5, 25 and 50 mg of Dinoprost tometamina) when applied on the 5th and 7th days of the estrous cycle. Three hundred thirty-nine (339) nonlactating Nelore cows were used. The animals were divided into two groups according to the onset of estrus, and received the PGF2&#945; dose on the 5th or 7th day of the estrous cycle. Each group was divided into three subgroups, which were submitted to the treatments of PGF2&#945; with dose of 12.5 mg, 25 mg or 50 mg. Through the P4 concentration, the rates of 1 and 0.5 luteal regression were estimated (1 - animals with P4 concentration below 1 ng/mL and 0.5 - animals with P4 concentration below 0.5 ng/mL). There was no interaction between the PGF2&#945; dose and the day of the estrous cycle. The PGF2&#945; application on the 7th day of the estrous cycle had higher rates of the 1 and 0.5 luteal regression, when compared to the PGF2&#945; application on the 5th day of the estrous cycle (1 - 76.9 vs 37.0 % - P = 0.0001; 0,5 - 57.5 vs 21.7 %, P = 0.0001, respectively). The rate of 1 luteal regression increased with the PGF2&#945; dose (12.5 mg - 39.0 %; 25 mg - 56.9 %; 50 mg - 76.5 %, P < 0.0001). The average concentrations of P4, when the PGF2&#945; was administered on the 5th day of the estrous cycle, follow the partial luteolysis standard that dependent on the PGF2&#945; dose. When the PGF2&#945; is applied on 7th day of the estrous cycle, the average concentration of P4 drops dramatically from 0 to 24 h and it do not rise again in 48 h. The P4 concentration is lower in the 50 mg (0.51 ± 0.07 ng/mL), 48 h after the PGF2&#945; application. The luteolysis rate was low on the 5th day of the estrous cycle. The luteal regression percentage increased with increase of the PGF2&#945; dose. The objective of the experiment II was to evaluate whether the replacement of the GnRH applications by BE, ECP and eCG in the 5-day protocols of P4 cause double ovulation and if the use of 1 or 2 mg of BE at the beginning of the protocol influences the double ovulation rate. Eighty-five (85) multiparous Nelore cows were used. On day 0 of the protocol, the cows received a P4 implant and a dose of BE that depending on the treatment to which the cows belong (Treatment A - 1 mg of BE, treatment B - 2 mg of BE). Five days later, the device was removed and the PGF2&#945;, ECP and eCG were applied. In the experiment II, there was 6.5 % of double ovulation. There was no significant difference in the double ovulation rate, dominant follicle diameter on the 5th and 7th day of the protocols, and follicular growth rate between the treatments A and B. The 5-day protocol of P4 with BE, eCG and ECP caused a low rate of the double ovulation, and there was no difference between 1 or 2 mg of BE to synchronize the follicular development wave. The objective of the experiment III was to compare the onset and frequency of estrus and the ovulation and pregnancy rates among the protocols of 5 days of P4 with GnRH and 7 days of P4 with BE, ECP and eCG in nulliparous, primiparous and multiparous. Four hundred eleven (411) Nellore females were used (nulliparous - n = 198; primiparous - n = 80; multiparous - n = 133). In 7-day protocol of P4, the animals received an implant of P4 and BE on day 0. On day 7, the device was removed and the PGF2&#945;, ECP and eCG were applied in the cows. In 5-day protocol of P4, the animals received implants of GnRH and P4 on the day 0. On day 5, the device was removed and two doses of PGF2&#945; were applied with interval of 6 h. The animals that did not show estrus until the AI time received 100 mg of GnRH at this moment. The pregnancy rate varied according to the female category in both protocols (nulliparous - 41.0 vs 51.0 % - P = 0.1608; primiparous - 25.6 vs 31.7 % - P = 0.5513; multiparous - 58.4 vs 32.8 % - P = 0.0041, respectively). The rate estrus onset in the 5-day protocol of P4 with GnRH was lower for all female categories, when compared to the 7-day protocol (nulliparous - 95.8 vs 66.0 % - P <0.0001; primiparous 0 vs 48.7 %; multiparous - 76.9 vs 13.4 % - P <0.0001, respectively). The response in the 5-day protocol with GnRH was worse in multiparous cows. (AU)

• FAPESP's process: 11/16328-0 - Pharmacological manipulation of the estrous cycle in Nellore cows: i - effect of doses of PGF2a for luteolysis on days 5 and 7 of the estrous cycle. II - effect of replacement of GnRH by EB, in the 5Co-Synch program, at estrus detection and distribution.
• Grantee: Marcos Vinicius de Castro Ferraz Junior
• Support Opportunities: Scholarships in Brazil - Master