Induction of sexual activity in Dorper ewes: Effect of two intramuscular doses of progesterone vs. progesterone vaginal sponges + eCG

• Published in: Journal of animal science 2016-10, Vol.94, p.824-824
• Main Authors: Ordonez, J Z, Ángel-García, O, Carrillo, E, Luna-Orozco, J, Meza-Herrera, C A, Rodriguez, R, Véliz-Deras, F G
• Format: Article
• Language: English
• Subjects: Anestrus; Body weight; Estrus; Gestation; Ovulation; Pregnancy; Progesterone; Reproduction; Sexual behavior; Sheep; Sponges; Studies; Synchronism; Synchronization; Ultrasound; Vagina
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jam2016-1691

The use of intravaginal sponges is a high-cost treatment which requires trained personnel while can generate reproductive problems in the animals. Therefore, the use of intramuscular (im) progesterone (P4) could be an alternative to avoid such a scenario. The reproductive outcomes of Dorper anestrus ewes using different im doses of P4 regarding the use of P4-intravaginal sponges + eCG, was evaluated. The study was carried-out in northern Mexico during the anestrus season (26°N, February). Anestrus ewes (n = 52, 3-5 yr old) similar body weight (BW) and body condition score (BCS) were subjected to two transrectal ultrasound screenings on Days 14 and 7 prior to the onset of the experimental treatments to confirm the absence of functional corpora lutea. Thereafter, ewes were randomly distributed to three experimental groups: 1) IMG1 (n = 21; 41.7 ± 4.0 kg BW, 2.1 ± 0.2 BCS) receiving 30 mg-im of P4 on Days 5 and 2 prior to eCG administration, 2) IMG2 (n = 17; 41 ± 7 kg BW, 2.0 ± 0.6 BCS) receiving 20 mg-im of P4 on Days 5 and 2 prior to eCG application, and 3) IVS (n = 14; 41.5 ± 3.0 kg BW, 2.0 ± 0.2 BCS), receiving an intravaginal sponge Chronogest® during 6 d and removed 24 h prior to eCG application (d 0). The three groups received a single dose of 300 IU eCG im on d 0. Estrus activity was recorded after exposure to one sexually active male during 15 min twice per day (0800 and 1800 h) × 5 d. On Day 10, the percentage of ovulations across treatments was determined by detecting the presence of corpora lutea throughout ultrasonographic scanning (USS). Then, on Day 45, another transrectal-USS was performed to determine pregnancy rate. Estrus activity, ovarian activity and pregnancy were evaluated among treatments thru X2considering the daily and cumulative proportions of these variables (MYSTAT 12 X2 program). The percentage of estrus were different (P < 0.05) between all the groups (43% IMG1, 35% IMG2, and 100% IVS). The largest ovulation percentage and gestation rate (P < 0.05) were observed in IVS group (93% and 79%, respectively), and similar (P > 0.05) for both IMG groups (62% IMG1 and 59% IMG2 for ovulation percentage, and 24% for gestation rate in both groups). Results demonstrated a better reproductive performance of previously anestrus Dorper ewes treated with intravaginal P4-sponges + eCG with respect to those receiving the im administration of P4. In conclusion, the synchronization protocol using two injections of progesterone had less sexual respon