13 Evaluation of PG-3-G presynchronization in Ovsynch-P programs in lactating dairy cows: Preliminary results

Abstract

Presynchronization treatments associated with the Ovsynch protocol and its modifications have been used to improve reproductive performance in lactating dairy cows. Use of a PG-3-G protocol is indicated to increase the number of cows in the most ideal stage of the oestrous cycle (Days 5-9) at first gonadotropin-releasing hormone (GnRH) injection of the Ovsynch protocol. The objective of this study was to compare fertility of lactating dairy cows submitted to Ovsynch-P, preceded by PG-3-G protocol or not. A total of 86 Holstein cows [body condition score of 2.6 ± 0.2 (1-to-5 scale), 3 and 10 years old, mean milk yield of 28.1 ± 7.9 kg per day, and 118 ± 56 days postpartum period] maintained in a semi-intensive system were blocked by parity and date of calving and randomly assigned to groups: control (n = 44) and PG-3-G (n = 42). On Day -10 cows in the PG-3-G group received an injection of 500 µg of sodium cloprostenol IM (Estron, Agener União, Brazil), and on Day -7 they received 0.05 mg of Lecirelin IM (GnRH, Gestran, Agener União). On Day 0, all cows had the first dose of Ovsynch GnRH injection and a 1-g progesterone intravaginal implant (P4, Primer, Agener União). On Day 7, a dose of sodium cloprostenol was administered to induce corpus luteum (CL) luteolysis, and the P4 implant was removed. Forty-eight hours later, cows were injected with the second dose of GnRH and inseminated 12 to 18 h later. The presence of CL and ovulatory follicle (OF) diameter were determined by transrectal ultrasonography (Aquila, Pie Medical, Maastricht, the Netherlands) on Days 0, 7, and 9, and gestation diagnosis was done on Day 30 after AI. Statistical analysis was performed using ANOVA, chi-square, Mann-Whitney, and Pearson correlation tests in SPSS 18 (Armonk, NY, USA), considering P = 0.05 significant and a tendency when P > 0.05 but P = 0.10. Incidence of CL on Day 0 tended to be more frequent (P = 0.1) in the PG-3-G group (78.6%) compared with the control (59%), but CL presence on Day 7 did not differ (P = 0.98) between the groups (35 and 34%, respectively). Based on the odds ratio, PG-3-G cows were 2.16 times more likely to have a CL on Day 0. The mean diameter of OF on Day 9 was smaller (P < 0.05) in PG-3-G cows (12.6 mm) than in control cows (15.3 mm), and a negative correlation was detected (r = −0.29) between the presence of CL on Day 0 and the diameter of OF on Day 9 (P = 0.05). Pregnancies per AI tended (P = 0.08) to be higher in PG-3-G cows (52%) than in control cows (34%). In summary, cows submitted to presynchronization with the PG-3-G protocol presented higher frequency of CL on Day 0 and tended to have a higher pregnancies per AI compared with control cows.