Fat and lean Coopworth ewes that were daughters of fat and lean rams were joined with rams from the Invermay lean and fat selection lines to study the effects of genotype (fat, lean) and mid-pregnancy feeding level on foetal weight and ewe carcass measurements at day 135 of gestation. Ewes offered a high level of feed during days 30 to 100 of gestation gained 3% while those on a low level lost 9% of their day 30 live weight. All ewes were offered the same level of feeding from day 100 until slaughter on day 135. Mid-pregnancy nutrition had no effect on foetal weight. Litter size had significant effects on foetal weight (single 4.56 kg, twin 3.99 kg, triplet 3.24 kg). The weight of foetuses of the lean genotype adjusted for litter size and nutrition was 270g heavier (P<0.01) than that of the fat genotype. The weight of placenta, and placentome number/foetus decreased with litter size and were associated significantly with foetal weight. Fat genotype, however, had no effect on placental weight or placentome number. Fat genotype of the ewe and foetus did not affect a number of foetal skeletal size parameters but influenced foetal weight despite ewe nutrition. Consequently it appears that this influence on foetal weight is independent on any effect of the placenta per se.
Proceedings of the New Zealand Society of Animal Production, Volume 46, , 27-30, 1986
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