Meta-analysis of morphometric parameters of late-gestation fetal sheep developed under natural and artificial constraints.

A meta-analysis was performed to study the relationship between ovine fetal BW and body length during the last month of pregnancy in sheep gestated under normal conditions and under different natural and experimental maternal- placental- and fetal- directed constraints. Means of crown-rump length (CRL) and BW records, as well as means of calculated G index (GI, BW/CRL1.5), body mass index (BMI, BW/CRL2.0), and Ponderal index (PI, BW/CRL3.0) of 195 nontreated and 160 treated groups of lambs from 131 studies were investigated by ANOVA. the GI is a novel BW-body length index developed for sheep fetuses and newborn lambs. The analysis included the effects of study (n=131), treatment (n=38), average litter size (1 to 3), and days in pregnancy (120 d to lambing). The morphometric parameters were obtained on average on d 139 of gestation, when lambs in the nontreated groups averaged 0.50 m for CRL and 4.20 kg for BW. applying the different treatments caused substantial variation in fetal BW (from 2.5 to 4.9 kg), and somewhat less variation in fetal CRL (0.41 to 0.55 m), reflecting ovine fetal ability to adapt its growth to a variety of natural and experimental constraints. Some treatments affected (P<0.05) the fetal BW-body length relationship, as clearly reflected by the GI and BMI, but not by the PI. litter size and days in pregnancy had effects (P<0.05) on all variables. It was concluded that the severity of fetal intrauterine growth restriction (IUGR) in the case of multifetus pregnancies is comparable with the IUGR effects caused by experimentally induced fetal growth-inhibiting interventions, and that GI may be superior to BMI and PI in detecting interference with ovine fetal body proportion.