ESTROUS AND FERTILITY RESPONSES OF DAIRY EWES SYNCHRONIZED WITH COMBINED SHORT TERM GnRH, PGF2α AND ESTRADIOL BENZOATE TREATMENTS

The objective of this study was to asses the effectiveness of short term protocols (5–7 days) for the synchronization of oestrus in lactating ewes during the non-breeding season, using combinations of GnRH, PGF2 and estradiol benzoate treatments. One hundred and six adult cross-bred Altamurana ewes were divided into the following six treatment groups: (i) Group NT (N= 30), which served as the control, was exposed to fertile rams for a 20 days period; (ii) Group Fe (N= 15) received FGA intravaginal sponges (14 days) + eCG i.m. (Day 14); (iii) Group GP (N= 15) received a GnRH agonist (Day 0) and PGF2 (Day 5) i.m. treatment; (iv) Group GPG (N= 15) received a GnRH (Day 0), PGF2 (Day 5) and a second dose of GnRH (Day 7) i.m.; (v) Group GPE ewes (N= 16) treated with GnRH (Day 0), PGF2 (Day 5) and estradiol benzoate (EB; Day 6, 24 h after PGF2) i.m. treatment; (vi) Group EPE (N= 15) treated with EB (Day 0), PGF2 (Day 5) and EB (Day 6, 24 h after PGF2) i.m. treatment. Ewes were checked for oestrus and hand mated using fertile rams. Upon return to service the ewes were mated again. A definite effect of the treatments on the occurrence of oestrus was recorded, with a higher percentage of ewes (P < 0.01) exhibiting oestrus in the Fe (93.3%) and EPE (100%) groups, compared to the GPG (33.3%), GP (46.7%) and GPE (62.5%) groups. The interval to oestrus was shorter and more synchronized in the long term treated Fe group (P < 0.01). The fertility rates recorded were 36.7% (11/30) in the NT or control ewes, and 60.0% (9/15), 33.3% (5/15) and 26.7% (4/15) (not significant) in the Fe, GP and GPG groups, respectively. In the GPG group the fertility and prolificacy rates recorded were higher (80% and 175%), than in any of the other treatment groups. In the GPE group, 10 of the 16 ewes (62.5%) exhibited oestrus, but the fertility rate was significantly lower (20%, P < 0.01), compared to the other groups (GPG, 80%; GP, 71.4%; Fe, 64.3%). In Group EPE, despite having the highest percentage of ewes exhibiting oestrus (100%), none of the ewes lambed. The fertility achieved in all the short term treatment groups following natural service and oestrous synchronization indicate that the protocols used do not seem to interfere with the ewes natural cycle or with their fertility. Results indicate that between the short term treatments studied, the GP and GPG methods offer a potential alternative to the conventional long term protocol (Fe) for oestrous synchronization in dairy ewes. Further research is required regarding the use of estradiol benzoate to synchronize oestrus.