Effect of bovine somatotropin administration during the last trimester of gestation on maternal growth, and foetal and placental development in primigravid ewes

The effects of maternal nutrition and body condition on placental and foetal growth in the ewe

This study investigated the effects of maternal body condition and nutrition on placental and foetal growth in mid-gestation. Welsh Mountain ewes (n=24) of body condition 3.5 (high, H) and 2.0 (low, L) at mating, were fed either 100 per cent or 70 per cent of their daily maintenance requirements from day 22 of gestation, yielding four groups: H100 (n=5), H70 (n=6), L100 (n=7) and L70 (n=6). On day 65, placental and foetal parameters were measured. Whilst the placentome number tended to be lower in L than H ewes, the mean placentome weight was significantly greater in L100 than H100 animals. Nutritionally related changes in IGFBP expression within the placentome and intercotyledonary endometrium may explain these findings, with IGFBP-3 expression in the luminal epithelium and caruncular stroma of the placentome villi being inversely correlated to placentome number and the total placentome weight respectively. The foetal CRL was shorter and the ponderal index greater in L than H ewes. The foetal CRL was positively correlated to maternal IGF-I concentrations and the placentome number, although the foetal weight remained unaltered by treatment. This study therefore demonstrates that body condition and ration can alter foetal and placental growth, perhaps by modifying systemic parameters and uterine IGF expression.

Placental development and fetal growth in growth hormone-treated ewes

The effects of recombinant bovine growth hormone (bGH) treatment of pregnant ewes on maternal metabolism, placental development and fetal growth were examined in two studies. In a preliminary study (experiment one), single-bearing ewes were treated by twice-daily subcutaneous injection for 7 days with bGH (n = 8) at a dose of 0.15 mg/kg LW/day or with saline (n = 8) between days 101 and 107 of gestation inclusive. In experiment two, single- and twin-bearing ewes were treated for 14 days with bGH (0.15 mg/kg L W/day) (n = 10) or saline (n = 10) between days 70 and 83 or days 98 and 111 of gestation inclusive. Ewes were killed on the day following termination of bGH treatment and fetal and placental measurements recorded. Maternal plasma concentrations of GH, IGF-I and insulin were higher (P < 0.001) in bGH-treated ewes relative to saline-treated ewes in both experiments. Consistent across experiments was an increase (P < 0.05) in the weight of the myoendometrium in bGH-treated ewes. Treatment with bGH also increased the total weight of the gravid uterus (P < 0.05) in both experiments. Weights of the uterine fluids were increased by bGH in experiment one (P < 0.05), but an effect of the same magnitude could not be repeated in experiment two. In experiment one, there was a tendency towards increased mean fetal body weights after growth hormone treatment, although the effect was non-significant. In experiment two, treatment with bGH was associated with significantly (P < 0.05) higher fetal weights, but only at the later stage of gestation (day 112). This effect was additive with that of fetal rank. Exogenous bGH treatment had little discernible effect on measures of placental size. It is concluded that administration of exogenous bGH to pregnant ewes can stimulate fetal growth, but only after about day 100 of gestation. This response seems most likely to reflect changes in maternal nutrient partitioning or placental function, rather than placental size. These studies suggest a role for growth hormone of maternal or placental origin in the regulation of fetal growth.