The effects of season on placental development and fetal growth
in sheep
C.M.C. Jenkinson, S.W. Peterson, D.D.S. Mackenzie, S.N.
McCutcheon
Department of Animal Science, Massey University, Palmerston North,
New Zealand
Proceedings of the New Zealand Society of Animal Production 1994,
54: 227-230
Autumn-born lambs have been reported to have lower birth weights
than spring-born lambs by 0.4 to 1.0 kg, but the physiological basis of this
difference is unknown. This study examined the effects of season on fetal
growth and placental development independent of the confounding effects of
maternal nutrition. Romney ewes (aged 5 and 6 years) were randomly
allocated to groups mated in December (n=13) or March (n=13 with a similar
live weight at mating (55.6±1.8 vs 55.7±1.9 kg, mean±SE, P>0.10) and
managed for a similar live weight at day 140 of gestation (62.5±1.8 vs 62.9±1.9
kg, P>0.10). At day 140 of gestation, measures of fetal growth and placental
development, adjusted for litter size, were (December- vs March-mated):
individual fetal weight (4.15±0.16 vs 5.07±0.16 kg, P<0.001); total fetal weight
per ewe (6.42±0.18 vs 7.14±0.22 kg, P<0.01); caruncle number (114.5±4.1 vs
121.0±4.2, P>0.10); placentome number (89.4±4.2 vs 106.9±4.3, P<0.01);
caruncle occupancy, i.e. number of placentomes/number of caruncles
(0.79±0.03 vs 0.88±0.03, P<0.05); and total placentome weight (564.7±34.0 vs
679.0±34.9 g, P<0.05). These results suggest that seasonal differences in birth
weight of lambs are mediated not by differences in maternal nutrition but rather
by a direct seasonal effect on placental size (specifically the formation of
placentomes and hence total placental weight).
Keywords: NZSAPAB;
Season; birth weight; placental development; fetal growth; sheep.
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Last Updated 25-01-1997
