In sheep, chronic undernutrition during twin gestation abolishes birth weight sexual dimorphism, being partially restored by antioxidants supplementation. The aim was to evaluate differences in the maternal-fetal endocrine environment and its influence on the differential growth of female and male fetuses in ovine twin pregnancies with discordant-sex conceptuses maintained under natural undernutrition, and to assess the effect of antioxidant supplementation and concentrated feed. Three groups of ewes (n = 10 each) were compared: the control group (C) was maintained exclusively on natural pasture (∼70% of energy and 30% of protein requirements). From day 62 to term, treated groups received antioxidants (AOx) or concentrate (NS). At 117 and 142 days of gestation (dGA), maternal plasma samples were collected to measure estradiol, progesterone, and cortisol, while umbilical cord plasma samples were obtained to measure insulin, IGF-1, IGF-2, and fetal cortisol. Lambs were delivered by cesarean section at 142 dGA, body weight was recorded, and a fetal skeletal muscle sample was collected for mTOR analysis by Western blot. Treatments did not affect maternal hormones. At 117 dGA, AOx and NS supplementation increased fetal plasma concentrations of IGF-1 and IGF-2; conversely, male fetuses of the Control group had lower IGF-1 and higher cortisol concentrations than their female co-twins. At 142 dGA, male fetuses showed higher concentrations of insulin and IGF-1, which were consistent with the expression of activated mTOR in muscle. It is concluded that maternal undernutrition imposes a greater burden on male fetuses, suppressing the growth axis; antioxidants partly reverse this, whereas maternal concentrate supplementation largely restores it.

Arginine supplementation improves fetal growth and colostrum composition in nutrient-restricted ewes, but its high cost and ruminal degradation limit its practical use. N-carbamylglutamate (NCG), which stimulates endogenous arginine synthesis, and is not degraded in rumen, may be a viable alternative. This study evaluated the effects of oral NCG supplementation (60 mg/kg BW/day from day 100 of gestation to term) on undernourished twin-bearing ewes (~50% NRC requirements; NCG n = 20, Control n = 21). Maternal body weight (BW), body condition score (BCS), blood metabolites, placental traits, lamb body measurements, and colostrum composition were assessed. BW increased and BCS decreased over time (p < 0.0001), with no treatment effect. Lamb and placental traits were similar between groups. NCG supplementation resulted in a 15% higher plasma urea concentration (p < 0.03) and altered 21 serum metabolites, with reduced levels of valine, leucine, isoleucine, glycine, proline, and phosphate, and increased serine, ethanolamine, urea, and 2-hydroxyhexanoic acid concentration compared to CON animals. Colostrum from NCG ewes had a 21% higher protein (p < 0.04) and a 16% higher IgG content (p < 0.03) compared to CON animals. Although NCG did not mitigate the negative effects of maternal undernutrition on fetal traits, it influenced maternal metabolism and improved colostrum quality.

In rangeland systems, natural nutrient restriction (NR) elevates risk for small-for-gestational-age (SGA) lambs, yet some NR ewes deliver Non-SGA offspring. We evaluated whether fetal biometry and Doppler indices could differentiate those fetal growth trajectories. Ninety-five single-pregnant Corriedale ewes were assigned from gestational day (GD) 70 to term to NR grazing (n=72) or supplemented Controls (n=23) groups. Fetal biparietal diameter (BPD), femur length (FL), thoracic height (TH), and umbilical cord diameter (UCD) were assessed at GD80, GD95, GD110, and GD125. Resistance (RI) and pulsatility (PI) indices were recorded for the umbilical (UA), cotyledonary (CA), and uterine (UtA) arteries at GD80, GD95, GD110, GD125, and GD140. Within NR, offspring were stratified by birth-weight (BW) quartiles to define SGA (lowest quartile, n=18) and Non-SGA (highest quartile, n=18) groups. Prenatal biometry did not differ among groups. At birth, BW differed (p < 0.05) among Control (4.95 ± 0.10 kg), Non-SGA (5.33 ± 0.06 kg), and SGA (3.79 ± 0.11 kg), and BPD and FL were smaller in SGA vs Control and Non-SGA. UA-RI at GD125 was higher in SGA vs Non-SGA (p < 0.005). UtA-RI and UtA-PI were lower in mothers of SGA lambs at GD110 and GD125 (p < 0.05). CA indices did not differ. UA-RI at GD125 was associated with BW (R² = 0.15; p < 0.001). Associations between BW and UtA-RI and UtA-PI at GD 110 and 125 explained little variance (R² ≤ 0.08). Distinct uteroplacental and umbilical Doppler signatures differentiated SGA from Non-SGA trajectories before measurable divergence in fetal growth. Although UA-RI at GD125 demonstrates prenatal predictive promise, its accuracy as standalone indicator remains modest.

Nutrient restriction (NR) increases small-for-gestational-age (SGA) offspring; however, some NR ewes deliver Non-SGA lambs. We evaluated whether fetal biometry and Doppler indices could distinguish divergent fetal growth trajectories. Ninety-five single-pregnant Corriedale ewes were assigned to NR grazing (n = 72) or supplemented Controls (n = 23) from gestational day (GD) 70 to 140. Fetal biparietal diameter (BPD), femur length (FL), thoracic height (TH), umbilical cord diameter (UCD), and resistance (RI) and pulsatility (PI) indices in umbilical (UA), cotyledonary (CA), and uterine (UtA) arteries were assessed at several GDs. Offspring within NR group was stratified by birth weight (BW) quartiles as SGA (n = 18) or Non-SGA (n = 18). At birth, BW differed (p < 0.05) among Control (4.95 ± 0.10 kg), Non-SGA (5.33 ± 0.06 kg), and SGA (3.79 ± 0.11 kg), with reduced BPD and FL in SGA lambs. Prenatal biometry did not differ. UA-RI at GD125 was higher in SGA (p < 0.005) and associated with BW (R² = 0.15; p < 0.001). UtA indices were lower in SGA at GD110 and GD125 (p < 0.05) but weakly associated with BW (R² ≤ 0.08). Doppler differences were detected before measurable growth divergence but have modest predictive value.