Extended progesterone treatment stimulates follicular growth and improved fertility in suckled beef cows submitted to a timed artificial insemination protocol

BILBAO, M G; MASSARA, N; RAMOS, S; ZAPATA, L; FARCEY, F; PESOA, J; TURIC, E; VAZQUEZ, M.I.*; BARTOLOME, J.A*

THERIOGENOLOGY

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2016 vol. 86 p. 536 - 544

0093-691X

The main objective was to evaluate the effect of an extended progesterone treatment on follicular growth and fertility in postpartum suckled beef cows subjected to a protocol of synchronization of ovulation. In Experiment 1, cows (n = 24) received either a 2 g progesterone intravaginal device on Day -23 (Day 35 postpartum) or a 0,558 g progesterone intravaginal device, and 2 mg of estradiol benzoate on Day -9, device removal, 1 mg estradiol cypionate and PGF2 on Day -2 and TAI on Day 0. Metabolic status was assessed between Days -9 and -2. Ovarian structures and plasma progesterone were determined weekly from Day -23 to -9 and daily from Day -9 to -2, every 12 h from Day -2 to ovulation and weekly until Day 28. In Experiment 2, multiparous cows (n = 302) with BCS ≥ 4.5 received identical treatment than cows in Experiment 1 but on Day -2, cows received 400 IU of eCG of two different commercial preparations. Ultrasonography was conducted on Days -23 and -9 on a subset of cows (n = 40). Pregnancy was evaluated 39 days after AI. In Experiment 3, multiparous cows (n = 244) with BCS < 5.0 received identical treatment than in Experiment 1 but initiated on Day -18 and on Day -2 cows received 400 IU of eCG or no treatment. Ovaries structures were determined in a subset of cows (n = 31) on Days -3, -2 and -1 to evaluate follicular growth and on Day 10 to confirm ovulation. Pregnancy was evaluated 39 days after AI. In Experiment 1, plasma progesterone was higher in treated than control cows (P < 0.0001) during the first 14 days. The extended progesterone treatment tended to increase i) size of the largest follicle between Days -23 and -9 (Group by Day, P < 0.06), ii) size of the regressing follicle from Day -9 to Day -5 (Group by Day, P < 0.09) and iii) size of the dominant follicle from Day -5 to Day 2(Group by Day, P < 0.06). There was not effect of metabolic status or interaction between metabolic status and day on follicular growth. In Experiment 2, extended progesterone treatment tended to increase the size of the largest follicle between Day -23 and -9 (P < 0.06). There was no effect of Group, eCG, BCS and parity on pregnancy per AI. In Experiment 3, cows receiving eCG and an extended progesterone treatment had larger dominant follicle (P < 0.01). Both, extended progesterone treatment (P < 0.02) and eCG (P < 0.03) increased pregnancy rate. In conclusion, an extended progesterone treatment stimulated follicular growth postpartum and improved fertility only in cows with low body condition score.