Melatonin treatment during late gestation of undernourished ewes: lamb body temperature and mother–young behaviours after birth

Abstract

Context In extensive grazing sheep systems, pregnant ewes undergo periods of undernutrition because gestation coincides with winter when natural pasture is of lowest quantity and poorest quality. The lamb’s weight and thermoregulatory capacity, and the ewe–lamb bond at birth, may be compromised. Maternal melatonin treatment during gestation may reverse these effects. Aim The aim was to determine the effects of melatonin treatment of single-lambing, undernourished ewes during the last third of gestation on lamb birthweights and body temperatures, and on ewe–lamb interactive behaviour after birth. Methods At Day 100 of gestation, 39 single-bearing ewes received a subcutaneous melatonin implant, and 54 ewes served as controls with no implant. Throughout gestation, the ewes remained under extensive conditions grazing on natural pasture. Measurements were made of lamb birthweight, body temperatures (surface temperature by infrared thermography and rectal temperature), and ewe–lamb behaviours during a handling test at 6–17 h after lambing. Key results There was no effect of melatonin treatment on lamb birthweight or rectal temperature, or on ewe–lamb interaction behaviours. Hip minimum surface temperature was greater in lambs from melatonin-treated ewes than lambs from control ewes (21.2°C ± 0.9°C vs 18.8°C ± 0.8°C; P = 0.05), and there was a similar trend for hip mean surface temperature (24.6°C ± 0.9°C vs 22.3°C ± 0.7°C; P = 0.06). Rump surface temperatures were greater in male than female lambs: maximum (27.9°C ± 1.2°C vs 22.9°C ± 1.2°C; P = 0.01), minimum (22.2°C ± 1.5°C vs 16.7°C ± 1.5°C; P = 0.02) and mean (25.4°C ± 1.3°C vs 20.5°C ± 1.3°C; P = 0.02). Conclusion Melatonin treatment during the last third of ewe pregnancy slightly enhanced the surface temperature of lambs at birth but did not influence ewe–lamb interaction behaviour after birth (i.e. after establishment of the ewe–lamb bond). Implications Further study in more depth is warranted into the possible effects of maternal supplementation with commercial melatonin implants on lamb development, thermoregulatory capacity, behaviour and survival rates in extensive grazing systems, including the effect on ewe–lamb behaviours immediately after birth for both singletons and twins.