Exogenous melatonin improves ovine embryo viability in undernourished ewes during the breeding season

VAZQUEZ, MARIA ISABEL; ABECIA, J A; FORCADA, F; CASAO, A

Vancouver

Congreso; 17th International Congress on Animal Reproduction (ICAR); 2012

Society for Reproduction and Fertility

Season and nutritional condition could have significant effect on the reproductiveperformance in sheep, particularly in the semiarid region, where the availability of nutritionalresources are highly seasonally variable. Melatonin treatment is effective inducing cyclicity andincreasing ovulation and lambing rates during anoestrus. On the other hand, undernutritionincreases embryo mortality and decreases pregnancy rates in ewes. The aim of this study was toinvestigate the effect of exogenous melatonin on ovulation rate, recovered ova and embryoviability in undernourished post-partum ewes during the reproductive season. The experimentaldesign involved 24 adult non-cycling, post-partum ewes, with a mean (±SEM) live weight (LW)of 65.9±1.8 kg and mean of body condition (BC) of 2.8±0.06. At parturition (November), eweswere treated (+MEL) or not (-MEL) with a subcutaneous implant of melatonin (Melovine®,CEVA). After 45 days, both groups were synchronized with an intravaginal progestagen for 14days and fed to provide 1.5 (Control, C) or 0.5 (Low, L) times daily maintenance requirements.Thus, experimental groups were: C-MEL, C+MEL, L-MEL and L+MEL. At oestrus (Day=0)ewes were mated and on Day 5 embryos were recovered by mid-ventral laparotomy andclassified according to their developmental stage and morphology. After embryo collection,ovaries were recovered and processed for IVF. After the period of the experimental diets, LWand BC of C-MEL and C+MEL ewes did not change significantly, but ewes in groups L-MELand L+MEL had an average weight loss of 9.6 and 10.5 kg, respectively (P<.001). No effect ofdiet or melatonin treatment was observed on ovulation rate and number of recovered embryo perewe. Number of viable embryos per corpora lutea from L+MEL (0.50±0.2) was significantlyhigher than L-MEL (0.12±0.1), C+MEL (0.20±0.1) and C-MEL (0.30±0.2) (P<.05). Overall, themelatonin effect was particularly evident in undernourished ewes, increasing both viability(L+MEL: 65 %; L-MEL: 25 %; P<.05) and pregnancy rates (L+MEL: 66.6 %; L-MEL: 16.6 %;P<.05). Neither nutrition and melatonin nor their interaction had a significant effect on the invitro oocyte development. Melatonin tended to increase the number of cleaved oocytes inundernourished ewes (L+MEL: 6.8±1.3; L-MEL: 3.9±1.3, P<.09) but number and rate ofblastocysts were similar between groups. In conclusion, this study shows that treatment withmelatonin implants at lambing during the breeding season improves the viability of embryosrecovered from undernourished ewes, although this effect seems not to be mediated at theoocyte competence level. Thus, use of melatonin implants even during the breeding seasoncould be a helpful tool, particularly when embryo development is affected by negative factors asundernutrition or post-partum periods.