Abstract:
Although body condition score was not significantly different between light(<55 kg, n = 6) and heavy (≥60 kg,n = 70 ewes at mating, it declined between Day 30and Day 90 of gestation in light but not heavy ewes, and remained lower up toterm. All ewes bore twins, delivered near term (Days 144-146) byCaesarean section. One lamb was immediately placed into a warm (30°C; WD)and its twin into a cool (15°C; CD) ambient temperature, and tissues weresampled at 0·5 h or 6 h. All CD lambs born to light ewes exhibitedhypothermia and/or respiratory failure and did not survive longer than 30min; these symptoms were not observed in their WD twins or any lamb born toheavy ewes. Total lamb birth weight, placental weight and fetal cotyledonaryweight were lower with light than with heavy ewes. Lambs born to light eweshad less perirenal adipose tissue and smaller liver, heart, kidneys, brain,adrenals and thyroid, although their heart, brain and pancreas represented alarger proportion of total bodyweight; pancreas weight was similar to that inlambs born to heavy ewes. Hence, maternal bodyweight critically influencesplacental weight and lamb size and survival after birth.