Fetal Brown Fat Deposition Is Increased By Melatonin Implants in Sheep

The major cause of lamb mortality in grazing systems at birth is starvation and/or exposure to cold complex, with hypothermia being a primary contributing factor. In precocial species like sheep, the ability to produce the heat required to prevent hypothermia during the first 12h after birth relies heavily on the non-shivering thermogenesis, via brown adipose tissue (BAT). Thus, insufficient BAT deposits, or inability to metabolize BAT, are the major factors contributing to lamb death resulting from starvation/exposure. Circulating concentration of melatonin is associated with proper amount and functionality of BAT. However, there is limited information on the effect of increased melatonin levels, via maternal supplementation, on fetal BAT deposition. The objective was to establish the effect of melatonin implants (M), in single- and twin-bearing ewes, on fetal BAT deposits. Corriedale ewes were synchronized, superovulated, mated to Suffolk rams and managed under commercial grazing conditions. Single (S)- and twin (T)-bearing ewes received either 0 (M0), 1 (M1) or 2 (M2) commercial 18-mg melatonin implants (Regulin®) at 100 days of gestation (n=8 per group). Ewes were euthanized at day 140 of gestation and total fetal perirenal fat (BAT) was excised and weighed. The effect of litter size (S vs T), number of implants (M0, M1 or M2) and their interaction on fetal biometrics were analyzed using ANOVA. A rank by treatment interaction (P = 0.002) was observed for total BAT, where SM2 tended to have 18% more BAT compared to SM0 (P = 0.1) and SM1 (P = 0.09) fetuses (22.8±1.6 vs. 19.3±1.5 or 19.2±1.5 g), while TM1 had ~35% more BAT compared to TM0 (P = 0.0002) and TM2 (P = 0.0003) fetuses (22.9±1.1 vs 17.1±1.0 or 16.9±1.1 g). Single and twin M2 fetuses tended to be 5-8% heavier compared to single and twin M0 and M1 fetuses (4.1±0.1, 3.8±0.1, 3.9±0.1 kg, respectively; P = 0.09). In addition, M2 fetuses, compared to M0 and M1 fetuses, showed greater fetal thorax diameter (34.6±0.4, 33.8±0.3, 33.9±0.3 cm, respectively; P = 0.047) and presented a trend for increased crown-rump length (44.1±0.5, 43.0±0.4, 42.6±0.5 cm, respectively; P= 0.056). These results indicate that maternal melatonin implants from day 100 of gestation increases BAT deposition, especially in twin fetuses, and may increase body weight. Both effects may have important implications for newborn lamb survival under commercial grazing conditions.

*Funded by CONICYT Project N°11150998