INFLUENCE OF MATERNAL BODYWEIGHT ON SIZE, CONFORMATION AND SURVIVAL OF NEWBORN LAMBS

Although body condition score was not significantly different between light (<55 kg, n = 6) and heavy (greater than or equal to 60 kg, n = 7 ) ewes at mating, it declined between Day 30 and Day 90 of gestation i n light but not heavy ewes, and remained lower up to term. All ewes bo re twins, delivered near term (Days 144-146) by Caesarean section. One lamb was immediately placed into a warm (30 degrees C; WD) and its tw in into a cool (15 degrees C; CD) ambient temperature, and tissues wer e sampled at 0.5 h or 6 h. All CD lambs born to light ewes exhibited h ypothermia and/or respiratory failure and did not survive longer than 30 min; these symptoms were not observed in their WD twins or any lamb born to heavy ewes. Total lamb birth weight, placental weight and fet al cotyledonary weight were lower with light than with heavy ewes, Lam bs born to light ewes had less perirenal adipose tissue and smaller li ver, heart, kidneys, brain, adrenals and thyroid, although their heart , brain and pancreas represented a larger proportion of total bodyweig ht; pancreas weight was similar to that in lambs born to heavy ewes. H ence, maternal bodyweight critically influences placental weight and l amb size and survival after birth.