Undernutrition and exogenous melatonin can affect the developmental competence of ovine oocytes

VAZQUEZ, M.I.; FORCADA, F; CASAO, A; ABECIA, J A; C. SOSA; PALACÍN, I

Roanoke, Virginia, USA

Congreso; 16º International Congress on Farm Animal Endocrinology; 2008

This study evaluated the effects of exogenous melatonin and level of nutrition on oocytecompetence, in vitro fertilization (IVF), and early embryonic development in sheep duringanestrus (AS) and the reproductive (RS) season. Adult Rasa Aragonesa ewes were assignedrandomly to one of four treatment groups in two experiments based on a 2×2×2 factorialdesign. Half of the individuals were treated with a subcutaneous implant of melatonin for 42 d(+MEL) and the others were not (‐MEL). For 20 d from the onset of a progestagen treatment tosynchronize estrus to slaughter, 5 days after estrus (Day 0), treated and untreated animals werefed either 1.5x (control) or 0.5x (low) the daily maintenance requirements. Ovaries werecollected and oocytes were used for IVM, IVF and embryo culture. Season had a significant(p<0.01) effect on the number of oocytes recovered (RS: 19.6 ± 1.0; AS: 14.5 ± 1.0) and thenumber of healthy oocytes (with several layers of cumulus cells and a uniform cytoplasm) (RS:13.9 ± 0.7; AS: 9.0 ± 0.7). In the RS, neither nutrition nor melatonin had a significant effect onthe evaluated oocytes quality parameters although melatonin implants appeared to reduce thenumber of unhealthy oocytes in the undernourished group (P < 0.05). During AS, inundernourished ewes exogenous melatonin tended to increase the number of healthy oocytes(L+MEL: 9.4 ± 1.0, L: 7.6 ± 1.4; P < 0.1), and significantly improved both cleaved oocytes (L+MEL:7.0 ± 0.7, L: 4.1 ± 0.9; P < 0.05) and blastocyst rate (L+MEL: 37.2, L: 21.9%; P < 0.05). Inconclusion, oocyte competence in ewes was affected by season, and melatonin implantsappeared to improve developmental competence in the seasonal anestrous period, particularlyin experimentally undernourished ewes.