COMPARISON BETWEEN THE 5-DAY COSYNCH AND 7-DAY ESTRADIOLBASED PROTOCOLS FOR SYNCHRONIZATION OF OVULATION AND TIMED ARTIFICIAL INSEMINATION IN SUCKLED BEEF COWS

BILBAO, MARÍA GUILLERMINA; ZAPATA, LUIS O.; ROMERO HARRY, HERNÁN; PÉREZ WALLACE, SANTIAGO; FARCEY, MARÍA FLORENCIA; GELID, LUCAS; PALOMARES, ROBERTO A.; FERRER, MARÍA SOLEDAD; BARTOLOMÉ, JULIÁN A.

THERIOGENOLOGY

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2019 vol. 131 p. 72 - 78

0093-691X

The objective was to compare pregnancy per AI and follicular dynamic in suckled beef cows treated with either a 7-day progesterone + estradiol-based protocol (7-d P+E group) or a 5-day progesterone Cosynch protocol (5-d P+CoS) for timed artificial insemination (TAI) during four breeding seasons. We hypothesized that estrus cycle status, days postpartum (DPP), fat depth and plasma progesterone concentration differentially modify the effect of treatments. Every year, 9 days before initiation of each breeding season, cows with more than 30 DPP were randomly assigned to one of two groups. Cows in the 7-d P+E group (n = 428) received a 0.5 progesterone intravaginal device (DIB) and 2.5 mg of estradiol benzoate on Day -9. On Day -2 the device was removed, and cows received 0.125 mg of cloprostenol and 0.5 mg of estradiol cypionate. Forty-eight hours later (Day 0) cows received TAI. Cows in the 5-d P+CoS (n = 428) received a DIB, and 100 μg of GnRH on Day -8. On Day -3, the device was removed, and cows received 0.125 mg of cloprostenol. A second dose of cloprostenol was given on Day -2. Cows received 100 μg of GnRH and TAI 72 h after device removal (Day 0). On Day -9, estrus cycle status was determined. In a subset of cows (n = 79) the size of the dominant follicle was determined between Days -2 and 0. In another subset of cows (n = 340) DPP, fat depth (mm) and plasma progesterone concentration (ng/mL) were evaluated on Day -9. Pregnancy per AI was determined 30 d after TAI. Pregnancy per AI was higher for cows in the 5-d P+CoS group than for cows in the 7-d P+E group (50.9 % vs. 41.3 %, P = 0.01) and was also higher in cyclic than in anestrus cows (54.3 % vs. 33.2 %, P < 0.0001). There was also a significant effect of breeding season (P = 0.0002) and sire (P = 0.03), and an interaction between treatment group and breeding season (P = 0.03). The dominant follicle was larger (P < 0.0001) in cows in the 5-d P+CoS group than the 7-d P+E group (10.7 ± 0.29 mm vs. 9.0 ± 0.28 mm). Considering days from prostaglandin treatment, the dominant follicle was also larger (P = 0.01) for cows in the 5-d P+CoS group (10.1 ± 0.30 mm vs. 9.0 ± 0.30 mm). Pregnancy per AI was higher in cows with ≥ 55 DPP ( 47.0 % vs. 29.6 %, P = 0.001), fat depth ≥ 0.50 mm (44.7 % vs. 29.7 %), and with high (≥ 1 ng/mL) plasma progesterone concentration (47.2 % vs. 28.7 %, P = 0.01). In cows with high plasma progesterone concentration on Day -9, pregnancy per AI was higher in the 5-d P+CoS group (60.5 %) than in the 7-d P+E group (34.9 %), but there was no difference between treatment groups in cows with low plasma progesterone (P = 0.07). In conclusion, the 5-d P+CoS protocol resulted in higher size of the dominant follicle and pregnancy per AI in suckled beef cows subjected to TAI. Estrus cycle status, DPP, fat depth and breeding season also affected pregnancy per AI. The increase in pregnancy per AI with the 5-d P+CoS protocol was greater when plasma progesterone concentration at initiation of the treatment was higher than 1 ng/mL.