The Effects of a Novel Follicle Wave and Heat Synchronization Protocol on the Follicles, Circulating Hormones, and Estrus of Anestrous Ewes.

Reproductive performance in seasonally anestrous ewes is poor even after the use of current controlled breeding protocols. Anestrous ewes treated with a medroxyprogesterone acetate sponge, for 12 or 14 d, and estradiol-17β (E₂) have synchronized follicular wave emergence. The objective of this study was to determine the effects of an E₂ injection 6 d after CIDR insertion on follicles, E₂ and LH concentrations, and estrus in seasonally anestrous ewes. Ewes (n=13) received CIDRs (Day -12) followed by an injection of eCG (500 IU; i.m.; Day 0) at CIDR removal and an injection of sesame oil without (1 mL; i.m.; Control) or with E₂ (350µg; i.m.; Day -6) 6 d before CIDR removal. Treatments were balanced for age, parity, and BCS. Blood samples were collected every 6 h for 48 h after E₂ injection and every 3 h for 60 h starting 18 h after eCG injection to determine LH concentrations. Blood samples were collected on Day -6 and 0 and every 6 h for 60 h starting 18 h after eCG injection to determine E₂ concentrations. Ovarian ultrasonography was done on Day -6 and 0. A ram was introduced on Day 1 to observe estrus. Ewes treated with E₂ had higher LH concentrations (0.37±0.05 ng/mL) than ewes treated with oil alone (0.12±0.05 ng/mL) during the 48 h after E₂ injection (P<0.005). Concentrations of LH were highest at 18 h after E₂ injection (1.11±0.12 ng/mL; P<0.001). Ewes treated with E₂ had higher LH concentrations (2.10±0.18 ng/mL) than ewes treated with oil alone (0.12±0.16 ng/mL) at 18 h after E₂ injection (P<0.001). The interval from eCG injection to the start of the pre-ovulatory LH surge was similar (37.1±4.4 h; P>0.05), but was more synchronized in ewes treated with E₂ (2.3±0.6 h) than ewes treated with oil alone (12.0±5.1 h; P<0.01). Concentrations of E₂ were similar between treatments on Day -6 (2.1±0.3 pg/mL; P>0.05) and Day 0 (2.3±0.4 pg/mL; P>0.05). Concentrations of E₂ tended to be highest at 18 h after eCG injection (3.5±0.5 pg/mL; P=0.076). Maximum follicular diameter was larger on Day 0 (4.8±0.2 mm) than Day -6 (3.4±0.2 mm; P<0.001). There were no differences in the interval from eCG treatment to the start (37.6±2.7 h) or end (74.7±1.9 h) of estrus (P>0.05). Adding an E₂ treatment during a CIDR-eCG estrus synchronization protocol increased LH concentrations after E₂ treatment and stimulated a more synchronized pre-ovulatory LH surge in seasonally anestrous ewes.