Influence of maternal bodyweight on adaptation after birth in near-term lambs delivered by Caesarean section.

The present study investigated the influence of maternal bodyweight on adaptation after birth in near-term lambs delivered by caesarean section. One twin lamb from a heavy (>60 kg) or light ewe (<55 kg) was randomly taken and immediately placed into a warm (30 degrees C) ambient temperature and its twin then delivered into a cool (15 degrees C) ambient temperature. Continuous recordings of colonic temperature were then made followed by measurements of thermoregulation and brown adipose tissue function up to 6 h of life. Following caesarean section delivery colonic temperature rapidly declined over the first 30 min of life, a response that was greater in lambs at 15 degrees C. Irrespective of ambient temperature all lambs born to heavy ewes commenced shivering within 15 min of birth and were able to restore body temperature. These adaptations were only observed in warm-delivered lambs born to light ewes, as cool-delivered lambs failed to shiver, became hypothermic and 4 out of 6 lambs exhibited respiratory failure. Umbilical vein plasma thyroid hormone concentrations were lower in lambs born to light compared with heavy ewes. Plasma T3 concentrations remained lower in warm-delivered lambs born to light ewes until 2 h after birth when heat production and colonic temperature were not significantly different from warm delivered lambs born to heavy ewes. Lambs born to light ewes possessed less brown adipose tissue than those born to heavy ewes. In conclusion, maternal bodyweight has a critical influence on survival following caesarean section birth that is dependent on the ambient temperature into which a lamb is delivered.